Carb issues

[M0WBY]

Hi

OK guys... I have been reading up on issues relating to my Layla (81 CB650C US import). Basically it only runs on choke and only on two cylinders!

I am going to go and buy a compression tester on monday to test the compression. It is not running on cylinders 3 and 4. I am suspecting that, since it only has 25K miles, and due to it standing since 2003 that the piston rings are stuck. The received wisdom as far I can tell is to not worry about it and get a few miles on the clock and they will free up of themselves.

The only problem is I need to get it running right first. All indications are that I have carb issues that need sorting! Now my bike had VB44A carbs but two of them were scrap. I don't know what was in them but it was nasty! Like black paint stripper! I have a set of VB54A carbs off a french CB650 on it at the moment. But the jets and air screws are off a set of VB54B carbs. The jets are #90 they are smaller that the ones from the VB44A as originally fitted which were #120. I may have a go with the VB54B carbs and see what that does. I have a problem though. The VB54A and VB54B carbs both have two air pipes on them that I don't know what they are for! Or where they should connect to! Are they just harmless air vents or am I missing a trick here or what?

http://www.flickr.com/photos/discoclover/sets/72157631764843253/

I have tried winding out the air screws until they are nearly falling out and it still won't run with the choke off!

Help!

Cheers

John

[M0WBY]

Hi

My compressions readings on a warme up engine (well running on 3 cyl with choke for 10 mins) are...

cyl 1 left 120PSI
cyl 2 left inner 120PSI
cyl 3 right inner 120PSI
cyl 4 right (not firing) 110PSI

I tried to down another test with a tea spoon of oil added but I could not find a way to get it into the middle cylinders. I need a pipette or something!

I have to admit that my 12mm adapter was not very good so the results are not quite what they should be.

So what do I know now... I am confused!

Help!

Cheers

John

[tom400f]

Hi John

The internet is your friend (of course you may have already found these...)
Compression:
http://www.hondacb650.com/viewtopic.php?f=4&t=1369
http://forums.sohc4.net/index.php?topic=15840.0
so it seems that can be left for now at least.

With the basic stuff like valve clearances and ignition timing checked you will have to get your carbs sorted. You are off to a difficult start with the hybrid affair you have got. Something must connect to those pipes you showed because they have clips on them. Here's a manual:
http://cosky0.tripod.com/
but not the same carbs as yours though.

Promise of other manuals here but you'll need to join the group: http://autos.groups.yahoo.com/group/Honda_CB650/?yguid=178049669

I reckon it will continue to cough and splutter until you strip, clean, service and adjust them properly.

[tom400f]

More info about those mystery tubes, possibly. May be they just vent:
http://forums.sohc4.net/index.php?topic=100351.95

[UK Pete]

slow running jets blocked is my bet
pete

[M0WBY]

Hi

They are between 1 and 2 carbs and 3 and 4 carbs. They seem to be just vents...

I have had the carbs off and checked every thing even again. Replaced all the o rings again. There does not seem to be any air leaks.

I took the air screws out and put a tube over their hole and blew out the slow running jets but they all seemed to be clear.

It has intermittent running on cyl 3 and will not run at all on cyl 4. It only runs on 3 when on full choke. It will now tick over, sort of, off choke but as soon as you try and rev it up it dies as it is only running on two cylinders. It is sparking I checked that and the timing. I checked the rocker gaps.

I think I am going to have to pull the top end off the engine and see what is going on... :-(

Booooo!

[Bitsa (Ralph Wright - RIP)]

Hi Mowby,
Not that I have done much work on the CB650 but they can not be much different to all the other fours.The things I would do is first set everything to the book air screws etc.Before trying to start the engine check all the plugs are sparking as you crank her over by the crankshaft.Point gaps are correct open carb bowel screws to make sure fuel flows out freely from all four.The compression to me sounds OK and if she only runs on choke definitely sounds to me fuel starvation.Open each bowel screw turn the fuel on and if no steady flow open the tank filler cap and if flow increases you now the filler cap vent is blocked.All the time you are messing with fuel lots of rag and no smoking please.Once you determine all four spark and all plugs are getting wet she should start OK.Once all four headers warm up then you can fine tune with balance and air screws adjust.After all this and no go I would then start to think about naff valves etc.I like the sound of you and only wished I lived near to you as I would have liked to help you out I could do with the company.Do not be to hasty to strip her down yet.With these old classics you must consider Rome was not built in a day some guys I have met have taken at least two years to get perfect.Keep your chin up you will get there.The carbs I sent you did you strip them,use carb cleaner everywhere blow compressed air through every orifice and reassemble to the best of your knowledge.I do not mean to underestimate your cababilities but I had to do mine several times as I took for granted that a shop that ultra sound cleaned them was it.No it was not.I wish you luck and keep going as I said you will get there and when you do you will think I fracking sorted that.
All the best
Bitsa

[K2-K6]

As Bitsa says, be careful of the fire risk and if you are getting petrol all over the place then do it outside as you only have to save the bike and not your garage as well.

Just some basics to add to the others: switch the plugs about to make sure that the problem isn't one or two of them.

Compressions sound as if they would be ok to run without any particular problems.

If you can get it running at a fast idle then blow some petrol down the #4 carb (you can just use a long thin tube in you mouth to suck a small amount up and blow it into the carb mouth) to see if it will actually run on that cylinder, this would verify the carb if it did.

Check to see if the valves are opening on number 4 as well.

As Bitsa says I wouldn't pull it apart just yet as it may well be outside the engine and you'll do the other work for nothing.

Try running it in the dark to see if you have any sprks coming out the HT leads and not reaching the plug when in normal running configuration, specifically where the plug leads go past the head castings.

Try switching the 1 and 4 HT leads over (they are both fired at the same time) to see if #1 stops and #4 starts.

Let us know how you get on.

[M0WBY]

Hi

The float heights on the CV (VB44 and 54) carbs are not adjustable oddjob.

I have fuel in all the carbs so I don't think the petrol tap could be a the issue but I am not ruling it out. I will do the test Bitsa suggested and/or remove and clean it out anyway just to take it out of the equation.

I suspect fuel starvation is part of my problem but I think there is another issue as well. 

I have no garage so I have to do all my spannering outside but I am looking at renting a garage from a friend just as soon as he gets a roof on it!

I am going to investigate the sparking side of things again. On the 650 it has an electronic ignition as per http://www.jasonkent.ca/manuals/79%20CB650%20Service%20017.pdf (which is 79 manual - but the manual is the same for mine for this section). I will perform all the tests starting at the top and working my way down to see if I have missed something. It has new plugs so they should be OK but I can swap them over it is no big issue. I may replace the HT leads whilst I am at it. 

I am thinking weak spark. It sparks at the plug on cyl 4 when I took it out and tested it but what it is doing under compression is another matter! I am thinking perhaps a pulsar or CDI unt is going bad or even a coil? But it is sparking fine on the other cyl, and it uses the same system for cyl 1 and 4, so the only thing it should be if it is a weak spark is the HT lead surely? Is there any reason why I can't just chop up and use a 7mm silicone car HT lead?

I just wish I had someone local who could look over it and give an alternative perspective on things.

Cheers

John

[M0WBY]

Hi

Had a good session on the bike today checked the ignition system working from the spark plugs back. I checked the timing and it is spot on. Replaced the HT leads anyway. I can defo say it is not for lack of spark that it is not running on cyl 4. Also cyl 3 is still only running intermittently and does not really kick in unless it is either on full choke or when warmed up only really kicks in past 5K rpm. So I think I can rule out the ignition system! Straws have all been clutched at and been found wanting! It is not the ignition that is to blame!

I double treble checked the tappets again. I can confirm they are all correct. I checked that they were turning over with the covers off and can say that this side of the engine seems to be pukka!

So I have two options. Either it is a sticky valve and/or piston rings on cyl 4 and it also has a bit of fuel starvation.

So I checked the fuel side of things. I noticed that the fuel pipe was a bit too long and went upwards after it left the tap and the fuel delivery is not strong enough as it has only gravity allowing the petrol to flow. The slightest uphill bit in the pipe effectively slows the flow down to a dribble! So I shortened the pipe as much as I could. On my American VB44 carbs they have this part that runs off the vacuum in cyl 2 by an attachment screwed into the balancing screw hole. This has a pipe to something that is attached to the carb rail. This has one tube to the petcock and another that attached to the petrol intake on the carb and another that vents to fresh air.  There now follows some more straw clutching... 

I am wondering if the american petcock is the wrong one for my carb system. The CB650 night hawk has a vacuum operated petcock http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=221129886560&fromMakeTrack=true&ssPageName=VIP:watchlink:top:en. I am thinking I may need a vacuum operated petcock on mine. That one of the pipes could possibly be for a vacuum system all thought neither seems to suck or blow as far as I can tell... Bloody things doing my swede... thoughts please gents! I am thinking I may have to try reinstating the american system and block off the two vent pipes just to see if that is the issue causing my fuel starvation issues!

Anyway whilst it still is not running right it is better than it was. It is not back firing so much or coughing as much as it did! When fully warmed up it will run at about  6-7K rpm without the choke but it needs the choke 1/4 out to tick over and run below 5K rpm. No matter what I do it won't run at all on cyl 4 despite having a good spark. The plug comes out wet suggesting that fuel is getting through. I think I will have to rip this engine apart! That is the way I am leaning towards.

Ho hum...

Cheers lads for reading my moaning!

John




 

[hairygit]

Is the plug wet with petrol or oil?

[M0WBY]

Petrol

[M0WBY]

Hi

As long as it does not have broken piston rings then I am hoping a good hone and a new set of rings ought to sort it out plus some new valves and/or valve seats.

I think this is why matey boy got shot in the first place... came in only running on two cylinders. Then sat around for a decade. Then he finally thought about doing something with it realised it was shagged and thought I wonder how I can get myself out of this hole. So he got a bent MOT and put it on the bay carefully managing to not mention the bit about it needed a rebuild and blaming the poor running on the carbs!

Oh well you gotta make mistakes to learn from them!

Ce la vie! I think a few beers to drown my sorrows is in order!

But I still want to get to the bottom of the fuel starvation thing!

Cheers

John

[M0WBY]

Hi oddjob,

I used the whole bank of VB54a carbs so they have the same float levels in all of them. The only thing that I needed for them off the bank of VB54b carbs were the jets and air screws. I put the old VB44a carbs in my parts bin should I need bits off them in the future (read about 10 years down the road they will be on ebay because I can't remember why I ever kept them!)

The VB54a carbs I got off Bitsa where superb quality and look as if they are practically brand new! Which is quite a feat for a set of 30 year old carbs!

I don't know if the float levels are different between the 3 sets or not so I did not chance it.

Cheers

John

[M0WBY]

Hi

Got it running real sweet on 3 cylinders! I tought well seeing as I will have to rebuild it anyway I thought to hell with it and I rode it around the block over and over again until the fuel starvation cleared! Anyone fancy a triple?

Going to pull this engine apart and see what it is doing! I reckon the head gasket is shot on number 4 cylinder. The symptoms are lack of compression on one cylinder, there is a spark but it just keep getting the plug wet and not firing, and it is chucking oil out the breather pipe.

Nuts!

John