Post by: Martin6 on May 17, 2023, 02:38:58 PM
I had a minor blow from the head gasket, which became a small drip whenever I stopped and popped it on the side-stand. I investigated the nuts visible next to the spark plugs. One of them (next to cyl no.3) was so loose I could turn it with my fingers. Cyls 2 and 4 were also not very tight. When the previous owner bought my bike, he found a handwritten note stating the piston rings had been replaced. The bike has done 650 miles since then. I'm guessing it has settled and requires a re-torque. That's my experience with old British twins, don't know if that happens on the CB750?
I've tightened them up and I think it is much improved. I would also like to check the rest. Is it possible to check and tighten the remaining head nuts, without removing the engine?
Thanks,
Martin
Post by: Nurse Julie on May 17, 2023, 02:55:55 PM
Post by: Bryanj on May 17, 2023, 05:52:24 PM
Having said that some of our US cousins like to leave the engine for 24 hours and re torque anyway as, also as Julie says the rocker cover can not be removed with engine in standard frame
Post by: Martin6 on May 17, 2023, 07:45:06 PM
Also, I know about the tightening sequence, but my feeling was, on balance, leaving the nuts loose was more likely to warp the head, than tightening them, especially as the nut close to cylinder 1's spark plug was fully tight.
Further investigation, I was cleaning up the front fins using compressed air to blow out engine degreaser. In the corner of my eye, I saw something vibrate. It was the top of a bolt I'd not previously noticed. It is completely free. I think it has sheared. Initially I was puzzled, as I can't see the bolt mentioned in the factory service manual, but I found a brief mention in the Haynes book and to a similar one at the rear of the head: "Do not overlook the two small bolts in the centre (front and rear) of the cylinder head." I am now feeling a bit dejected! What do they say, "buy in haste..."
I am desperately trying to avoid engine out. I don't think I have the skill to tackle something as complicated as this motor. I've done a lot on my Norton, but not full engine surgery. I've only done that on a small 2-stroke, which is a much easier proposition. Once the engine's out, given some of the things I've found and the mileage (40,000), it would deserve a thorough inspection and a fair bit of preventative work. Probably the cost of sending it to someone trustworthy, if I can find someone, is likely to be beyond me at the moment. I was hoping for 1 or 2 seasons of riding, before getting to major jobs... Not sure what to do.
As the weep is fairly minor, at the moment, I'm tempted to just ride it and save up for work to be done over the winter, either later this year, or next.
Post by: Bryanj on May 17, 2023, 09:24:20 PM
Download the honda manual, get a 3/8 drive six sided socket set, cirlip pliers and torque wrench plus a mate to help lift the engine out.
Post by: Martin6 on May 17, 2023, 09:27:09 PM
I've got the manual and that's what's putting me off! ;D
Post by: McCabe-Thiele (Ted) on May 17, 2023, 10:13:29 PM
There are videos on U tube plus loads of members here who will lend their experience and advice f.o.c.
You are never too old to learn new skills if you have the time.
Take plenty of pics on your phone and get that engine out !
Post by: Matt_Harrington on May 18, 2023, 08:06:36 AM
Bryan,
I've got the manual and that's what's putting me off! ;D
Manuals are always daunting! Bryan is right and it will never be as bad as you thought it could be.
I'd be a bit worried about running the engine and creating damage that may cost more in the long run.
Post by: SeanFD on May 18, 2023, 08:52:07 AM
I did a nut and bolt restoration of my 750 that had sat in boxes for 30 years and my only previous experience was on a CB125S back in 1976.
Apart from all the advice and support you'll get here, have a look at these videos; I found them very useful.
https://www.youtube.com/watch?v=MkHJuU01-Wk (https://www.youtube.com/watch?v=MkHJuU01-Wk)
Ignore the "cafe racer" bit, its a CB750 total rebuild – in 40 episodes.
He's not infallible, but honest enough to admit a mistake if he makes one; I pointed out and error and a week later he had added a comment to the video.
Post by: Sesman on May 18, 2023, 09:10:20 AM
Post by: McCabe-Thiele (Ted) on May 18, 2023, 09:26:06 AM
I switched on the captions and would pause at what seemed like complicated stuff.
When unsure I would post pics & ask here - yes some jokes but the feedback from a handful of members was invaluable.
https://www.youtube.com/watch?v=NQgwhv8v6Os
Post by: Laverda Dave on May 18, 2023, 10:07:44 AM
Post by: Martin6 on May 18, 2023, 11:06:20 AM
I guess, running it, I have the risk that if the head is not warped, it could warp over time. It runs sweet enough now. It's not using oil, just a couple of drips onto the floor off the front left fin, when on the sidestand after a run. That's what alerted me. I've since noticed a slight film on the engine cases, now im looking for it. But not bad.
I guess in part it's confidence. Am I skilled enough to measure all the tolerances (bearing shells, valves etc.)? What do I do if the head is warped? Am I capable of removing and replacing the key bearings? Will I know what a worn gearbox looks like... etc. Oh, and the hardest one, how do I explain it to my wife ;D
Then there's the list of expensive bits I might find. Plus the bits I should change as I'm in there and 40,000 miles may not be the end of life, but I don't want to go back in there shortly after. Things like I guess, I should change the cam and primary chains after 40,000 miles, probably everything rubber, like the tensioners, valve seals?... As I say, a bit daunting. Then there's special tools. Engine stand at the least. I'm guessing, but parts alone could easily be over £1,000? :-\
Feels like a big decision.
Post by: Nurse Julie on May 18, 2023, 11:31:53 AM
Post by: Bryanj on May 18, 2023, 11:41:45 AM
You need a clutch nut special tongued socket, but if its ever been off bet it was butchered with hammer and punch.
You need an alternator rotor puller, which is a bolt with the correct thread.
Main and big ends you can normally say if they look good they are but you can use plastigauge to check.
You do need a decent torque wrench, preferably 3/8 drive as there are plase 1/2 inch drive sockets wont fit.
Hondabond and graphogen will probably be the most expensive non honda part.
Yes all rubber bits, they have been getting rock hard for decades.
Post by: SteveW on May 18, 2023, 11:47:51 AM
I found that the replacement head gasket was 0.1 mm thicker than the original and the new o-rings for the oil feed to the cam were 0.4mm thinner than original.
So a total of half a mm under size.
I wasn’t going to risk it leaking so I sourced some o-rings half a mm over size and no leaks at all in 200 or so miles.
The gasket set was NE brand from David Silvers.
Post by: McCabe-Thiele (Ted) on May 18, 2023, 11:55:49 AM
Post by: Laverdaroo on May 18, 2023, 07:46:19 PM
These motors aren’t that complicated, especially after working on ducatis and other European temperamental lumps. The crowd on here have your back and you shouldn’t have a worry doing it. If you can work on a trumpet you’ll breeze the 750 motor. It’s not one big job, it’s just a selection of little jobs. Easily said but keep telling yerself that and the nerves will go. Go for it, it’s really satisfying. Don’t forget though it’s a 40 odd year old bike, they can’t run brilliantly all the time, you’re the new custodian, make it how you want it and don’t be scared or apprehensive about it, it’s not as hard as you think. Just follow the process and you’ll be away
Sent from my iPhone using Tapatalk
Post by: Bryanj on May 19, 2023, 07:47:11 AM
Post by: Martin6 on May 19, 2023, 07:49:58 AM
Post by: Bryanj on May 19, 2023, 08:55:37 AM
Post by: Matt_Harrington on May 19, 2023, 09:35:34 AM
Post by: Martin6 on May 27, 2023, 02:03:47 PM
👍
I think I'm going to have to do something about the suspension though. Too bouncy, front and rear, on my local roads.
Post by: Martin6 on May 30, 2023, 03:06:23 PM
I have the Haynes and Honda manuals and have watched a few YouTube videos to familiarise. I've ordered an engine stand, so I can work on a workbench. The bike has done 41,000 miles. I have nothing to suggest the angine cases have ever been apart before. I'm thinking I'll go as far as replacing the cam and primary chains and anything rubber (seals and chain tensioner rubbers).
- I already have a full gasket set from David Silver, are these good enough?.
- Are there any 'special' tools you would recommend me to get hold of?
- From your experience, are there any other parts I really should replace, regardless of apparent condition?
Thanks 👍
Post by: Bryanj on May 30, 2023, 05:22:42 PM
Remove points plate and advacer before lifting out and be careful not to bend the stud.
No need to remove generator rotor unless you have starter problems as no crank seal that side, oh and you need a set of seals for the engine
Post by: Martin6 on October 25, 2023, 10:21:48 AM
The engine is out. Head and barrels off.
I found significant damage, beyond repair, to the gasket surfaces between the head and valve cover, where it had been jemmied off at some point. This was definitely one of the leak points. Gouges were deep, across the entire width of the gasket surface, including around the screw hole. A difficult repair, which i would have to put out for welding (if possible). I decided to find a replacement head and cover. I have found a 2nd hand replacement head (with valves) and a cover. They appear to match. Slightly different casting shape on the head's bottom cooling fins, but the gasket face, bolt and stud holes etc. are identical. I've been through the replacement head, thorough clean and compressed air, except for removing the 2 oil metering plugs. With the valve stem oil seals removed, there was a small amount of play in the axhaust valves / guides. I looked at the original damaged head and this was no different. It wasn't burning oil, so I will go with the replacement's guides and valves. Lapped the valves, new stem seals. I think it will be fine. ( after reassembling the valves, springs etc., I realised the springs go in a particular way round, tight coils at the head end. So I've had to do it again!)
I checked the valve timing before I started to remove the cam / tappets. It was out by one tooth of the cam sprocket. When the cam was at TDC, the crank was at 'F' on the points plate. Thankfully, there was no sign of piston to valve contact.
The bolt which is front centre, outside the cylinder head between exhaust 2 and 3, had indeed sheared. It is broken off at a point too deep inside the barrel casting for an eazi-out.
The cylinder barrel: All 4 cylinders were shiny, showing no sign of honing / cross hatching. There is a slight lip in the top of all 4 cylinders. There was carbon on the piston crowns, and the crowns have some wear (a couple have swirl marks, particularly no.2) but no damage. The rings were replaced 2,000 miles earlier. They were free and clean. Looks like the cylinders weren't honed for the new rings. The carbon on the crowns came off easily with brake cleaner and scotchbrite.
The cylinder barrels are now with a local engineering shop recommended to me. They will remove the sheared bolt / check the thread and believe the cylinders will be ok with a gentle hone / deglaze. I will check rig gaps, before reassembly.
I checked the primary chain from inside the sump, the tensioner is within spec at 68.24mm. The cam chain tensioner has plenty left and the chain does not appear worn, it was tight to get off the sprocket (tensioner removed) no tight links and resists 'lateral' movement. I think it's fine. The tensioner rubbers also look ok.
So, I am planning to leave the crankcase undisturbed.
In the cylinder head, I would like to remove the oil metering plugs and clean behind them. Compressed air does blow through ok, but I'd like to check. They don'twanttocome out. Is there a technique to removing them without destroying them?
Committed now! Much to learn. Advice gratefully received. Thanks.
Post by: Martin6 on October 28, 2023, 12:36:03 PM
Once I've cleaned the bores and oiled them, I think I'm ready to reassemble. I'll follow the book. Haynes and factory, although both seem to focus on earlier top ends. I'll aim to put the cylinders and head on today and torque it down. Mine had loose nuts and bolts when I took it apart, so I'll leave it overnight and check the torque again, before moving onto the cam and valve gear assembly. This is a first and I'm nervous ::)
- Are there any tips you would give?
- I've seen mention of applying a light coat of gasket sealant to the plastic / rubber pucks. Is that a good thing to do?
- gasket sealant anywhere else? It seems odd not applying anything to the gasket surfaces at the base of the barrels and the head.
Thanks, Martin
Post by: Martin6 on October 29, 2023, 02:07:52 PM
Does anyone have the right dimensions for the rings and a good source?
Thanks, Martin
Post by: Pauarc on October 29, 2023, 05:07:23 PM
Part fish for head
Paul
Post by: Martin6 on October 29, 2023, 06:59:43 PM
Hi MartinWell done, thank you. 11mm x 2.5, = 16mm o.d. Must be it.
Part fish for head
Paul
Appreciated.
Martin
Post by: Martin6 on December 14, 2023, 11:07:42 PM
I replaced a lot of the head nuts, bolts and screws and engine mount hardware, repainted the engine and had the frame and brackets powder coated, whilst the engine was out. I also found the cause of my stiff front suspension, a slight bend in one of the stanchions. So I replaced that and the fork oil seal. New Hagons on the rear.
It's looking quite tidy. Fingers crossed it will run well. I'm aiming to go for a run tomorrow in the sunshine. Maybe get 30 miles on it and check it over a few times. I'm thinking I'll change the oil and filter at 100 miles. Does that seem sensible?
Martin
Post by: Skoti on December 15, 2023, 07:13:39 AM
If you find lots of stuff in there then pull the oil filter for inspection as well.
With Honda engines cleanliness is next to godliness!
Good luck
Skoti
Post by: davidcumbria on December 15, 2023, 07:21:55 AM
Post by: Pauarc on December 15, 2023, 09:00:48 AM
it’s great to hear bike back together hope the first run out goes smoothly good luck Paul
Post by: Laverda Dave on December 15, 2023, 09:55:05 AM
I would change the filter as well as the oil even though it will only have 100 miles on it, for the sake of a tenner it worth it for piece of mind and it gives you the opportunity to inspect it for any contamination.
Post by: Martin6 on December 15, 2023, 11:07:45 PM
A friend saw no smoke, except at one point when I opened up to accelerate hard, producing a whiff of black smoke. Running rich maybe?
Couple of questions:
I've a slight hesitation applying the throttle from tickover and a bigger hesitation if I rapidly whack the throttle on whilst riding (c.3500rpm). It's fine if I just roll the throttle on in a more measured way. Are these symptoms of running too rich?
I seem to have a wandering oil level on the dipstick. Was at 80% when I started out. Was just above the minimum 40 miles later, then at 75% when I got home. All readings were taken on the centre stand,.on level ground. Oil return looks consistent when I check in the tank. For the last of the readings, I put it on the sidestand before lifting it onto the centre stand. Can't see how that would affect the tank level though? In your experience, is this odd, or usual behaviour?
Minor observations:
I'm not convinced the tacho is calibrated correctly. 1400rpm sounds and feels like a nice gentle tickover. Below that just feels too slow. I'm yet to do a running carb balance though. The speedo is definitely reading fast by more than I'm used to. I'd say indicated 60mph is really a tad over 50mph. A local radar speed awareness sign shows 30mph when I have 36 on the speedo! I'll live with that.
Thank you for encouraging me to give the rebuild a go. I have a huge sense of achievement and feel like this is now my Honda CB750, my 'pride & joy'! The manuals (Haynes and Honda) were good start points, but a bit tricky on model variations over the years. Most problems I stumbled into were solved without too much drama, via searches here and on SOHC4 forum. Only a little blood was shed in the process!
I'm looking forward to next year with my bike, although with my fingers crossed for now.
👍 Best,
Martin.
Post by: McCabe-Thiele (Ted) on December 16, 2023, 05:00:31 AM
Post by: Johnny4428 on December 16, 2023, 09:58:03 AM
Post by: Martin6 on December 17, 2023, 10:45:24 PM
Great news Martin! So impressed you managed out this time of year for a “shakedown” run. Wouldn’t be too concerned about the oil level, I’ve had that on my 750, after all the engine is where you want the oil to be not the tank. Well not all of it anyway. Bit of syncing and tuning to do by the sounds of it but plenty of winter ahead yet!🥶
I'd guess it's a little bit warmer and a lot dryer down here! I'm able to pick my days and ride all year with a few mates. Bacon and eggs are a great winter warmer! Although, some of the winter runs, I stick to a modern bike with a big enough alternator for a heated jacket.
I was out again today, warmed the engine through and up to nearly 100 miles, so I could change the oil. I'm really pleased, it was lovely and clean and I dissected the filter, which was also clean. I'd also unwound the air screw on carb no.1 by 1/8th of a turn. Initial impressions are it is better, but forgot to check the plug before restarting the bike to check new oil level. Still so far, so good :) 👍
Post by: Oddjob on December 17, 2023, 11:46:01 PM
I ran with some really powerful magnets on the outside of my cannister filter, on my CB1300, around 6-8 IIRC, the idea was that any metal would stick to the outside of the cannister due to the magnets, when I removed the cannister I cut the housing in half so I could see if there was anything there, there wasn't. Saying that, alloy would not be attracted but you can't win all the time.
Post by: Martin6 on December 18, 2023, 08:12:56 AM
Edit: it's not diligence, more like lack of confidence I could have got it right 1st time!
Post by: K2-K6 on December 18, 2023, 09:31:58 AM
As long as you put in the correct volume at change of oil it won't give problems, but may initially give a little confusion.
The bulk of the oil should be in the tank (as any dry sump system will be like this) with as much supply volume available to the pump, and then onwards to galleries as possible.
Dry systems work on having greater volume through scavenge, back to tank, than delivery to always ensure oil available to pressure side of pump. Interupted supply (depleted tank reservoir) leads ultimately to catastrophic oil starvation in extreme cases.
Manual says run until warm, switch off, then immediately (it doesn't say immediately) but you don't need a "settling" time on dry sump system, to check running level in tank.
There's no dipstick in engine as oil should not be reservoired there. If it is, then there's a fault and usually with stop valve that prevents flow from draining tank into engine while not running.
If checked after being out on a run, then left overnight and checked (before starting) again, with a drop between these two measurements you'd suspect the stop valve seals.
Usually dipping the tank at any point really should give virtually the same result, or very close in range. Big variation and you'll need to consider working on the pump to fix further potential problems.
Post by: Martin6 on December 18, 2023, 11:40:31 AM
This was variations whilst still hot. I'll watch it, but I think it's probably fine.
The thing I'm most nervous about is still having signs of the sooty plug on no.1 and a bit on no.2 and not taking off when i more aggressively whack on the throttle. I think that suggests it's too rich, but not sure about that?
Along with the bad oil leak, this was one of the reasons i took on the engine refurb. The carbs were cleaned out thoroughly with carb cleaner and compressed air. Needles on middle grooves, bench synch'd to get reasonably close, using a drill bit method. Air screws initially at 1 turn out. Float heights double checked with a vernier guage on the inner flat area of the bowl edge. New rubber seals on the carb tops. No sign of splits in the rubber manifolds.
Can timing is fine and points / ignition timing (also no.4 is running clean). Tappets were set carefully when the cover was off.
Not sure where to go on this? It's a pain cleaning the plug every 200 miles, which is what I was doing. I've had one thought, I didn't clean out the exhaust headers, which were sooty on 1 and 2. Is it possible the sooty plugs could be due to transfer from the headers? But that wouldn't explain the bogging down. All a bit confusing...
Post by: Skoti on December 18, 2023, 01:36:31 PM
Although I first wasted cash on new main and idle jets which made no difference whatsoever.
Oh and BTW it's better to use genuine Honda needle jets and needles, after market stuff sometimes gives flat spots when accelerating as the needle profiles are not exact.
Good luck
Skoti.
Post by: K2-K6 on December 18, 2023, 01:47:55 PM
Unusual circumstance......we had on here a partly blocked header pipe that did similar. Effectively this prevents full exhaust of burnt mixture, to combine new intake fuel volume with oxygen depleted mix and give incomplete burn. This is what exhaust gas recirculation does by bleeding in carbon monoxide to reduce the burnable mixture (accompanied by reduction in fuel injected obviously) and provide reduced effective volume under light loading. Clearly undesirable if present here though.
First suspect is always the air passages feeding the idle circuit, if not absolutely clear then the idle circuit runs at full "choke" as soon as you start it. With no air....or substantially restricted supply....the carb venturi sucks at maximum demand through only the idle jet dipped in fuel of float bowl. This will play havoc with any setup logic. Absolute certainty is required on this circuit to stop it running you ragged.
Crude test to see what response you get is too wind those idle airscrew in and out while running to gauge if there's competent response from each one that's suspect.
More advanced...with help from friendly MOT tester.....get each pipe measured when bike is working temp. Looking at HC to assess the unburnt hydrocarbon content should build you a picture to at least understand where it currently is in mixture terms.
Bench sync is fine for how you are, it won't generally correct anything jetting wise...unless very seriously out of kilter anyway. I wouldn't look at that as suspect.
Post by: K2-K6 on December 18, 2023, 02:08:02 PM
"Thanks. I have a dry sump system on my 850 Commando, so I know about 'sumping' :)
This was variations whilst still hot. I'll watch it, but I think it's probably fine."
Yes, worthwhile monitoring as these generally don't do it. Maybe not as strong as "never" to describe, but when healthy and with regular usage its not a risk as they are particularly reliable in that respect, with any significant swings giving cause to investigate further.
Post by: Martin6 on December 18, 2023, 05:13:52 PM
I will have another look at the carbs. I used a carb refurb kit when I first got the bike (as it was non-running) from David Silver. I kept the needles, jets and screws the carbs came to me with, so I'll clean them and the carbs and try the old ones again. No idea whether they're original Keihin brass though. I suppose it's possible, but unlike,y after 47 years and 42,000 miles!
I will monitor the oil level carefully. I think it's not wet sumping. I filled the engine about a week before the first run and it stayed at a constant level in the garage. I'd put 1/2 Litre of oil each side of the head (through the rocker covers) and 2L in the tank. The low dipstick reading was the first check, on the first ride after putting the engine back together. So, I just assumed it was low due to the pump filling all the remaining oilways, plus filter. So, it was surprising to see it back to nearly full when I next stopped. That struck me as odd. On the oil change I did yesterday, after filling the tank (2.9L) , it dropped a little when I ran it for 2 minutes, to 75% on the dipstick. I'd guess that was oil filling the filter and sump. I ran it again and it stayed at 75%. So far, so good. Just that first reading on the first ride that's throwing me. I'll keep checking.
Post by: Skoti on December 18, 2023, 06:27:32 PM
Instead of the the 3.5 litres stated on the oil tank sticker, 2.7 litres of oil does mine when changing the oil and filter.
When cold mine shows about 85% dipstick level and when up to normal running temp it's about 100% and seldom varies.
But it's been already mentioned that it's no big issue as long as the oil tank level is some where between min and max.
Over filling could cause other problems.
As regards wet sumping mines sometimes does this when parked up over the winter, as a long suffering Commando owner I've a habit of dipping the oil level before each journey...
Hope you manage to iron out the post rebuild issues and enjoy miles of Honda reliability.
Post by: Martin6 on December 18, 2023, 09:33:32 PM
You may have already seen this, I use it on the Norton, it enables emptying the sump with the small drain plug, without wearing the threads in the crankcase: https://andover-norton.co.uk/en/shop-details/16995/magnetic-crankcase-sump-filter-kit
Yes, 3.5 Litres would also take me over max with the CB750. Not surprising I guess, as we'll never get all the old oil out, without a strip down. My factory manual suggests 2.9Litres as a start point for an oil change, run the engine for 2 minutes, then check the level. I did this and it was fine.
I'm sure I'll get there. I've really enjoyed my post rebuild rides, so I have every incentive to get it sorted. 👍 I'm in my late 50s. These 70s bikes were what I saw as 'the ultimate' as I was growing up, with no prospect of riding them at the time. The Norton and the Honda are still ideal bikes. Both quick enough, but in very different ways, so each is a different riding experience. At least, what I lose in the cost of parts, I save in depreciation and hopefully, at least one of them will be in working order at any one moment!
Post by: Martin6 on January 19, 2024, 05:38:37 AM
OK, thank you.I dusted off the needles and jets I had taken out of my carbs, when I replaced them with the refurbishment kit from David Silver (Keyster branded). I ŵas surprised to see the difference in the profile of the main jet needles. The old ones are a thicker diameter. I assume, at identical height setting, the old needles will allow a lower volume of fuel through, compared to the replacements. I thought this might explain the rich exhaust at open throttle and the bogging down. The jets and emulsion tubes look the same. I left the new jets in and went back to the old (clean) needles and emulsion tubes. Initial runs show an improvement. Must say, if this does solve it, I'm a bit annoyed that something sold as a direct replacement has caused me to chase my tail for 6 months.
I will have another look at the carbs. I used a carb refurb kit when I first got the bike (as it was non-running) from David Silver. I kept the needles, jets and screws the carbs came to me with, so I'll clean them and the carbs and try the old ones again. No idea whether they're original Keihin brass though. I suppose it's possible, but unlike,y after 47 years and 42,000 miles!
....
When the weather warms up a bit, I'll look at carb balance. I was close on the workbench, but it shows signs of the revs hunting a bit on tickover. I have spare fuel line, can anyone recommend a solution for a remote fuel reservoir? I'd prefer to keep my tank safely out of the way!
Post by: Skoti on January 19, 2024, 07:47:20 AM
You need to renew the needle jets as well, they are a press fit into the carb body under the emulsion tube you refer to.
Just tap them out with a pin punch from the top.
The needles will be worn as well, when compared to new ones you will see the lower part shiny where it enters the needle jet.
Genuine Honda needle kit 16012 392 004
I change mine at 12-15000 miles, by that time the consumption has gone up and it'll start almost without choke.
Good luck
Skoti
Post by: Martin6 on January 19, 2024, 08:36:39 AM
Martin,Does that kit work for a K6, do you know?
You need to renew the needle jets as well, they are a press fit into the carb body under the emulsion tube you refer to.
Just tap them out with a pin punch from the top.
The needles will be worn as well, when compared to new ones you will see the lower part shiny where it enters the needle jet.
Genuine Honda needle kit 16012 392 004
I change mine at 12-15000 miles, by that time the consumption has gone up and it'll start almost without choke.
Good luck
Skoti
Post by: Skoti on January 19, 2024, 08:52:08 AM
Listed on CMSNL web site as CB750K6 fitment as well.
Post by: McCabe-Thiele (Ted) on January 19, 2024, 10:02:13 AM
When the weather warms up a bit, I'll look at carb balance. I was close on the workbench, but it shows signs of the revs hunting a bit on tickover. I have spare fuel line, can anyone recommend a solution for a remote fuel reservoir? I'd prefer to keep my tank safely out of the way!
[/quote]
I bought a small plastic petrol tank off e bay it came with a tap& & pipe for around £12 a couple of years ago. Like below other similar ones on fle bay
https://www.ebay.co.uk/itm/276208145748?hash=item404f49d554:g:mcYAAOSwZ9tlbNIY&amdata=enc%3AAQAIAAAA8CD6Js4CpXVvA3gz1gwA1BJz0x53toQQ6l0zawe8klchV2Yyxq306AtZZJt8slKyqt9CRBks7GvzC4hZIZct%2FSRuIQnYx9aTBrXD%2FlCvVMRtau%2Fqj1nbNpreviuOLEKt3GwfwZEhCAq8f4tbwVwSElS1e0qOb5kRrY82AWe3O4%2B9KUfzWyKeE7uYK0%2BOsPDXy78rUtNbA5DOvvTMzbtL%2BEPFKwozYnbZ1jA0F0kJxtLrm9OU41CXbXF0StOA3KUuXB8s7an%2F7i%2BjhNATO5HmWSyAvP1pio90M6wCdVOdztbcJrbyoOQLYJVf5vXlpNdG0Q%3D%3D%7Ctkp%3ABk9SR5z1yZKkYw
Post by: Johnny4428 on January 19, 2024, 10:08:56 AM
This is what I have Ted very handy with the hook up facility.
Post by: McCabe-Thiele (Ted) on January 19, 2024, 10:16:32 AM
https://www.ebay.co.uk/itm/275326163846?mkevt=1&mkcid=1&mkrid=710-53481-19255-0&campid=5338723872&toolid=20006&customid=7XVaJu4bAAAAQYXzERG60rlTZbkhAAAAAA
This is what I have Ted very handy with the hook up facility.
Ideal if you are in a shed or garage with rafters - otherwise an old Hospital drip stand!
Post by: Martin6 on January 19, 2024, 12:38:25 PM
Post by: taysidedragon on January 19, 2024, 12:56:13 PM
Thank you, ordered the Sealey version, to hook on the rafters. 👍
I hook mine on the left hand handlebar. Similar height to the bike's tank.
Post by: McCabe-Thiele (Ted) on January 19, 2024, 02:00:20 PM
Thank you, ordered the Sealey version, to hook on the rafters. 👍
You might need to watch the header tank height as too high might cause the float valves to leak.
Post by: Johnny4428 on January 19, 2024, 03:15:49 PM
Post by: Oddjob on January 19, 2024, 04:40:57 PM
Thank you, ordered the Sealey version, to hook on the rafters. 👍
You might need to watch the header tank height as too high might cause the float valves to leak.
That I feel is a fallacy Ted, if it seals it seals, look at the video of that wreck that Johnny started up the other day, tank is very high in the rafters and that didn't leak, and they were PD carbs as well, known for causing problems. Sure pressure can cause problems but what weighs more, 3 gallons a few inches above or 1 pint a few feet above?
Post by: McCabe-Thiele (Ted) on January 19, 2024, 05:31:55 PM
Thank you, ordered the Sealey version, to hook on the rafters. 👍
You might need to watch the header tank height as too high might cause the float valves to leak.
That I feel is a fallacy Ted, if it seals it seals, look at the video of that wreck that Johnny started up the other day, tank is very high in the rafters and that didn't leak, and they were PD carbs as well, known for causing problems. Sure pressure can cause problems but what weighs more, 3 gallons a few inches above or 1 pint a few feet above?
The pressure is not affected by the fact that a tank holds 3 gallons - it's all about the pressure per square inch so a water tower at say 66 ft above ground level will have a pressure of about 30 psi to a tap at the bottom. A pint of water in bottle at 66 ft will have the same pressure of about 30 psi.
IIRC petrol is heavier than water but lets says it's the same weight per gallon as water. The pressure from the petrol tank if its a foot from top of fuel in tank to the carburetta will be what just under 0.45 psi. If the temporary tank is held at a height of 3 ft you are increasing the pressure to 1.35 psi so there must be a greater risk of a leak at three times the pressure.
That's my logic I'm open to being told where I am mistaken.
Post by: Oddjob on January 19, 2024, 06:07:22 PM
The fact that Johhnys didn't leak at that height (and TBH I've done the same myself, hanging the tank really high) means the float seat can handle that amount of pressure so long as it's in good condition, we blame the height of the tank for leaks when we should really be blaming a poor seat instead.
Post by: K2-K6 on January 19, 2024, 07:02:05 PM
1 ltr of fuel hung on the handlebars is exactly the same weight as it is hanging on the ceiling, just the volume of the pipe (minimal at that bore) is added to the total weight. If you had it on the bars with tube running horizontal to the carbs, then lifted it up high, you just add that tube volume in weight.
Water towers are about distribution over distance to supply surrounding areas I believe. The volume has to be above all of the outlet else the pressure will not be enacted at the outlet when you open that tap if its not reliably below the head tank.
Post by: McCabe-Thiele (Ted) on January 19, 2024, 08:52:30 PM
From my days of studying fluid dynamics (yep a long time ago 1971) the lecturer came up with the analogy that fluid pressure is in many ways equivalent to voltage in electronics. The higher the voltage/pressure the greater the ability to overcome resistance.
It's all about the pressure if it's imperial its pounds per square inch so within some limits depending on the friction in the pipe a doubling in pipe diameter does not change the pressure only the flow rate ability at any given height.
Post by: Martin6 on January 19, 2024, 11:02:47 PM
I don't have the maths to calculate the force required, (clockwise moments = anticlockwise, etc.) but my rafters aren't particularly high and my rope is longer than my spare fuel line ;D
Post by: Oddjob on January 20, 2024, 03:57:17 AM
My point being that a remote tank is pretty much never going to exceed the float valves shutoff systems limits unless you're going to extremes like hanging it off the chimney ;D
All that it may do is expose the inherent weakness in the system, a lot of people change these for stuff like Keyster and they ain't anywhere near as good as the original brassware.
Post by: Nurse Julie on January 20, 2024, 09:02:54 AM
Something I had to learn many years ago for the delivery of intravenous fluids to patients in intensive care wards, before calibrated fluid delivery pumps arrived on the scene.
Post by: Moorey on January 20, 2024, 10:04:31 AM
Typically mc fuel pumps delivers 3psi. Float valves are generally overcome at approx 4.5 / 5psi. 1ft head of water gives 0.433psi do the maths.
One thing many don't think of is that in use float valves open very tiny amounts so the smallest of debris is likely to stay in the valve and never
be flushed through unless the carb is drained or stripped and cleaned properly.
Anyone wanting to check simply put a airline with a pressure reg on a upside down carb on the carb inlet and see at what point the valve leaks
air when using leak detector spray.
Post by: McCabe-Thiele (Ted) on January 20, 2024, 10:57:19 AM
Typically mc fuel pumps delivers 3psi. Float valves are generally overcome at approx 4.5 / 5psi. 1ft head of water gives 0.433psi do the maths.
One thing many don't think of is that in use float valves open very tiny amounts so the smallest of debris is likely to stay in the valve and never
be flushed through unless the carb is drained or stripped and cleaned properly.
Anyone wanting to check simply put a airline with a pressure reg on a upside down carb on the carb inlet and see at what point the valve leaks
air when using leak detector spray.
Good point Moorey about the debris issue.
Post by: Oddjob on January 20, 2024, 12:34:48 PM
Post by: K2-K6 on January 20, 2024, 02:55:49 PM
Typically mc fuel pumps delivers 3psi. Float valves are generally overcome at approx 4.5 / 5psi. 1ft head of water gives 0.433psi do the maths.
One thing many don't think of is that in use float valves open very tiny amounts so the smallest of debris is likely to stay in the valve and never
be flushed through unless the carb is drained or stripped and cleaned properly.
Anyone wanting to check simply put a airline with a pressure reg on a upside down carb on the carb inlet and see at what point the valve leaks
air when using leak detector spray.
Isn't that accumulated figure 0.433 psi going downward under sea level ? Usually at one atmosphere for each 10.06 mtrs (33ft) effectively the accumulation of the ocean above you.
In air, and by lifting 1 ltr, then its nothing like that surely.
I'd doubt much difference between a tank say at 20 ltr sitting just above the carbs, in comparison to 1 ltr at 6 ft higher.
Post by: taysidedragon on January 20, 2024, 03:19:41 PM
Why use 6ft when you can just use 2ft? 🙂
Post by: McCabe-Thiele (Ted) on January 20, 2024, 03:45:49 PM
Typically mc fuel pumps delivers 3psi. Float valves are generally overcome at approx 4.5 / 5psi. 1ft head of water gives 0.433psi do the maths.
One thing many don't think of is that in use float valves open very tiny amounts so the smallest of debris is likely to stay in the valve and never
be flushed through unless the carb is drained or stripped and cleaned properly.
Anyone wanting to check simply put a airline with a pressure reg on a upside down carb on the carb inlet and see at what point the valve leaks
air when using leak detector spray.
Isn't that accumulated figure 0.433 psi going downward under sea level ? Usually at one atmosphere for each 10.06 mtrs (33ft) effectively the accumulation of the ocean above you.
In air, and by lifting 1 ltr, then its nothing like that surely.
I'd doubt much difference between a tank say at 20 ltr sitting just above the carbs, in comparison to 1 ltr at 6 ft higher.
The volume of petrol in either tank is not the issue here that would only alter the flow level if both tanks were of the same depth.
My previous sums were out by a factor of two as a 66 ft water tower would represent 2 Atmosphers about 60 psi not 30 psi - so a foot of water is around 0.9 psi the total volume of fuel in either the bike tank or the temporary one is irrelevant. So at 6 ft above the existing petrol tank of say 1-ft the pressure would rise from 0.9 psi with an increase of 6 x 0.9 = 5.4 making the total pressure at effectively 0.9 + 5.4 = 6.3 psi. This does not take into account the difference in density between water & petrol , all pressures are based on sea level.
Post by: K2-K6 on January 20, 2024, 06:01:27 PM
Can we apply the "atmosphere" calculation to a static head of fluid though ? The example of going down intomthe sea doesn't seem to apply to me as you are effectively within the fluid that is supported on the seabed. Each movement downward gives you a layer now above you that's compressive. The total gain taking into account that increases in mass to give the typical calculation figure.
In water tower or the high level fuel feed, the mass is supported through a route down to the ground and so doesn't enact a force on the outlet.
The column weight is what we could measure at base level, this then depending on bore size (capacity in vertical now unsupported by the structure) with a column of 60 ltrs that would be 60 kilos in water into whatever sized outlet we have.
Oil derived fuels are ordinarily less dense than water, but not by much to affect our consideration here.
It looks more like volume of pipe above float valve (possibly 100 ml ) when on ceiling, approx 100 grams resisted by the float force through leverage on the entry valve.
Post by: McCabe-Thiele (Ted) on January 20, 2024, 06:51:11 PM
My XJ900 petrol tank sprung pin hole leaks all along the bottom of the fuel tank due to standing over 10 winters or so. An Imperial gallon of water weighs 10 lbs an Imperial gallon of petrol weighs about 7.2 lbs so the heavier water sinks to the bottom.(I've looked it up).
Post by: Oddjob on January 20, 2024, 07:05:33 PM
Post by: Laverdaroo on January 20, 2024, 08:02:17 PM
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Post by: K2-K6 on January 20, 2024, 09:04:31 PM
All discussions are good I feel.
I was idly wondering recently about tbe famous Pink Floyd album cover that is clearly of Refraction, when if you were to be generally hanging around the Dark side of the moon, then would probably be seeing Diffraction, which wouldn't look like that.
;D ;D ;D
Post by: Laverdaroo on January 20, 2024, 09:34:39 PM
For no real purpose I find it interesting, along with other's views as that is how we acquire knowledge or exhamine our own.Pa ha ha haa, love it.
All discussions are good I feel.
I was idly wondering recently about tbe famous Pink Floyd album cover that is clearly of Refraction, when if you were to be generally hanging around the Dark side of the moon, then would probably be seeing Diffraction, which wouldn't look like that.
;D ;D ;D
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Post by: Moorey on January 20, 2024, 10:54:02 PM
Typically mc fuel pumps delivers 3psi. Float valves are generally overcome at approx 4.5 / 5psi. 1ft head of water gives 0.433psi do the maths.
One thing many don't think of is that in use float valves open very tiny amounts so the smallest of debris is likely to stay in the valve and never
be flushed through unless the carb is drained or stripped and cleaned properly.
Anyone wanting to check simply put a airline with a pressure reg on a upside down carb on the carb inlet and see at what point the valve leaks
air when using leak detector spray.
Isn't that accumulated figure 0.433 psi going downward under sea level ? Usually at one atmosphere for each 10.06 mtrs (33ft) effectively the accumulation of the ocean above you.
In air, and by lifting 1 ltr, then its nothing like that surely.
I'd doubt much difference between a tank say at 20 ltr sitting just above the carbs, in comparison to 1 ltr at 6 ft higher.
No just as a column of water lift the tank 10 ft and you will have 0.433 psi X 10 = 4.33psi at the pipe end. Volume in the tank is irrelevant.
A quick Google
What is the pressure exerted by a 1 foot column of water equal to?
Using Water as a Guide for Determining Pressure – Math for ...
0.433 psi
The relationship between water, height and pressure is constant. If we were to take a column of water 1 foot high and use a pressure gauge at the bottom to measure the pressure it would read 0.433 psi. This is our constant when dealing with water and it remains consistent as we add more water.
Post by: Moorey on January 20, 2024, 11:01:07 PM
Typically mc fuel pumps delivers 3psi. Float valves are generally overcome at approx 4.5 / 5psi. 1ft head of water gives 0.433psi do the maths.
One thing many don't think of is that in use float valves open very tiny amounts so the smallest of debris is likely to stay in the valve and never
be flushed through unless the carb is drained or stripped and cleaned properly.
Anyone wanting to check simply put a airline with a pressure reg on a upside down carb on the carb inlet and see at what point the valve leaks
air when using leak detector spray.
Isn't that accumulated figure 0.433 psi going downward under sea level ? Usually at one atmosphere for each 10.06 mtrs (33ft) effectively the accumulation of the ocean above you.
In air, and by lifting 1 ltr, then its nothing like that surely.
I'd doubt much difference between a tank say at 20 ltr sitting just above the carbs, in comparison to 1 ltr at 6 ft higher.
The volume of petrol in either tank is not the issue here that would only alter the flow level if both tanks were of the same depth.
My previous sums were out by a factor of two as a 66 ft water tower would represent 2 Atmosphers about 60 psi not 30 psi - so a foot of water is around 0.9 psi the total volume of fuel in either the bike tank or the temporary one is irrelevant. So at 6 ft above the existing petrol tank of say 1-ft the pressure would rise from 0.9 psi with an increase of 6 x 0.9 = 5.4 making the total pressure at effectively 0.9 + 5.4 = 6.3 psi. This does not take into account the difference in density between water & petrol , all pressures are based on sea level.
Where do you get 0.9psi from for a column of water 1ft high.
Post by: McCabe-Thiele (Ted) on January 21, 2024, 02:29:16 AM
Typically mc fuel pumps delivers 3psi. Float valves are generally overcome at approx 4.5 / 5psi. 1ft head of water gives 0.433psi do the maths.
One thing many don't think of is that in use float valves open very tiny amounts so the smallest of debris is likely to stay in the valve and never
be flushed through unless the carb is drained or stripped and cleaned properly.
Anyone wanting to check simply put a airline with a pressure reg on a upside down carb on the carb inlet and see at what point the valve leaks
air when using leak detector spray.
Isn't that accumulated figure 0.433 psi going downward under sea level ? Usually at one atmosphere for each 10.06 mtrs (33ft) effectively the accumulation of the ocean above you.
In air, and by lifting 1 ltr, then its nothing like that surely.
I'd doubt much difference between a tank say at 20 ltr sitting just above the carbs, in comparison to 1 ltr at 6 ft higher.
The volume of petrol in either tank is not the issue here that would only alter the flow level if both tanks were of the same depth.
My previous sums were out by a factor of two as a 66 ft water tower would represent 2 Atmosphers about 60 psi not 30 psi - so a foot of water is around 0.9 psi the total volume of fuel in either the bike tank or the temporary one is irrelevant. So at 6 ft above the existing petrol tank of say 1-ft the pressure would rise from 0.9 psi with an increase of 6 x 0.9 = 5.4 making the total pressure at effectively 0.9 + 5.4 = 6.3 psi. This does not take into account the difference in density between water & petrol , all pressures are based on sea level.
Where do you get 0.9psi from for a column of water 1ft high.
Actually I am wrong it will be half that as 14.7 psi is equivalent to a water manometer 33 ft in height at sea level.
So 33 ft of water exerts a pressure of approx 14.7 psi, divide 14.7 psi by 33 gives you 14.7/33 = 0.44545 psi per 1 ft column of water.
As petrol weighs around 7.2 lbs per gallon as against water weighing 10 lbs per gallon a one foot column of petrol would exert less pressue it would be 7.2 divided by 10 multiplied by 0.44545 psi i.e 0.3207 psi.
So if a petrol tank has a height of 1 ft between the fuel tank level & the carbs that would be 0.3207 psi exerted by the petrol.
Increasing the height some extra 6 ft up in the rafters from the tank level would be an additional 6 x 0.3207 =1.9242 psi so a new total of 1.9242+0.3207= 2.2449 psi.
My revised figures are only accurate to a couple of decimal places this leads me to the conclusion that Ken, Bryan & others are right that is unlikely to make the float needle leak under such a relatively low pressure.
My warning about hanging the reservoir in the rafters is clearly a load of Gonads it is unlikely to cause a healthy float needle to weep.
Pleased you pulled me up on my maths.
Post by: Oddjob on January 21, 2024, 02:34:34 AM
If nothing else it made people hone up on their maths skills. ;D ;D
Post by: McCabe-Thiele (Ted) on January 21, 2024, 02:44:10 AM
The reality of my twice revised figures now explains your decades of working experience to my complete satisfaction.
PS I've got a dose of Insomnia hence my posting at gone 2.00 am
Post by: Martin6 on January 21, 2024, 09:08:05 AM
Post by: Moorey on January 21, 2024, 10:30:44 AM
What, can't have this. Everyone's in agreement! Quick, someone start an oil thread... 👍
Who's to say I've done yet. I might want to throw Specific Gravity into the equation just to complicate matters. ;D
Anyone for ATF vs Fork Oil. ;)
Post by: Bryanj on January 21, 2024, 10:50:11 AM
Post by: McCabe-Thiele (Ted) on January 21, 2024, 11:39:39 AM
For no real purpose I find it interesting, along with other's views as that is how we acquire knowledge or exhamine our own.
All discussions are good I feel.
I was idly wondering recently about tbe famous Pink Floyd album cover that is clearly of Refraction, when if you were to be generally hanging around the Dark side of the moon, then would probably be seeing Diffraction, which wouldn't look like that.
;D ;D ;D
I saw the Australian Pink Floyd Dark Side of the Moon at Nottingham Concert Hall a couple of years ago.
As well as all the period backdrops for Another Brick in the Wall etc the funiest part was at the interval when I looked at the Blue Rinse set audience - the average age must have been close to 75 yrs with almost no one under the age of say 30!
There were Zimmer frames at the end of most rows - great live concert & light show.
Post by: Laverdaroo on January 21, 2024, 02:44:37 PM
Always makes me chuckle when instead of the inflatable pig, the giant 35’ blow up kangaroo comes out at the end…… brilliant
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Post by: McCabe-Thiele (Ted) on January 21, 2024, 04:11:04 PM
Post by: Laverdaroo on January 21, 2024, 07:51:38 PM
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Post by: Laverda Dave on January 21, 2024, 09:23:16 PM
Worth seeing if they are playing near you👍
Post by: taysidedragon on January 22, 2024, 12:28:53 PM
Brilliant show every time.
Post by: taysidedragon on January 22, 2024, 02:53:25 PM
It might be media hype but a member of the original Pink Floyd is alleged to have said "they are better live than we were".
I forgot to say that Dave Gilmour is so impressed that he hired them to play at his own birthday party one year.
Post by: SteveD CB500K0 on January 22, 2024, 05:45:52 PM
This is continental!
What was the original question?
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Post by: McCabe-Thiele (Ted) on January 22, 2024, 09:36:22 PM
One mention of the likes of Pink Floyd - we are drifting further than Phil on his Yacht when the wind has dropped. 8) 8) 8)
Post by: Martin6 on January 22, 2024, 11:04:08 PM
I suspect the cause of "Thread Drift" is related to the cold winter nights - as many of us are not actively doing much bike work in the cold we trawl this site looking for things to say or comment on.I managed to get out on my bike today, for a post carb synch shakedown. Ran very well. No bogging down, no oil leaks and, for the first time since I've owned it, all the plugs look similar, clean and non-sooty. The bike has fought me a lot of the way, so I'm not assuming anything just yet. But I allowed myself a self satisfied little pat on the back, for now. :)
One mention of the likes of Pink Floyd - we are drifting further than Phil on his Yacht when the wind has dropped. 8) 8)
p.s. I hung the Sealey tank from the rafters about a foot above normal tank height. It worked well.
p.p.s. The Clash and The Cure, never really got Pink Floyd 8)
Post by: McCabe-Thiele (Ted) on January 23, 2024, 01:33:05 AM