Honda-SOHC
SOHC.co.uk Forums => CB350/400 => Topic started by: Eldrick on September 19, 2022, 09:20:28 AM
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Is that possible that my carbs are having an out of body experience?
I removed the carbs a few months ago after the bike choked to a halt, out on a run. After that I removed the carbs from the block, checked and set the float heights and specifically replaced the Carburettor float valves in all four carbs as they were stuck solid.
I then followed Bryanjs’ ‘Basic bench carb balance guide', replaced the gaskets (top and bottom) on the carbs and mounted them on the bike again. The bike runs now, however I have an issue getting the bike to idle at anything near 1200rpm, it is more like a minimum of 2000rpm.
I removed the carb block again to bench sync again, mainly because I messed with the slide adjusters too much. I decided I got it benched properly and mounted the carbs on the block again. I also used a vacuum carbtune kit, the perfectionist in me insisted, I still cannot get the idle down to 1200rpm.
I have also checked and set each air pilot screw, could be naming those wrong, to 2 plus one half turn open. On the carb tune I can only match the carbs to within 10-8cmHg. So, carb 3 may be at 16cmHg and carb 4 would be at 24-26cmHg.
The main observation I had and the reason for the question:
Bryanjs’ ‘Basic bench carb balance guide‘ says about the slides; ‘Engine side, it has the flat bottom not the cutaway.' During my observations whilst doing this bench sync I could really tell there was a cut away on the slide so I proceeded working on the engine side, my brain is now convinced that there was a different shape to the slides on the air box side. Too late for that thought, the carbs are now on the bike again and I don’t mind removing them again to check.
Questions are;
1. Could the slides be on back to front?
2. Can the slides be extracted from all four bodies without removing the bodies’ from the block?
3. If 1 and 2 are possible and I fix the issue can I just use the vacuum sync and be confident that the carbs are performing optimally if I then get 1200rpm tick over and a balance of around 16-24 cmHg and all four within 3cmHg of each other?
ThanksKenny m
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The slides will only fit one way round as there is a groove down one side and a notch it slides down.
As a starting point I set my air screws at one and a half turns - it idles nicely at 1200 when up to temperature.
I assume you did not mix up the parts of each carb so the same slider goes in it's original carb. On these old bikes I also use an in-line filter due to the risk of debris from the petrol tank.
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Blocked pilot jets and/or pilot jet carb drillings is my guess.
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I did not remove the slides from the bodies at any point during my inspection/cleaning. That does not exclude some other owner having done that in the past. The question remains tho, could they be in the wrong body and therefore reversed?
I know about the grove on the slide, technical question; is that grove on the right hand side for all four slides? If so, then I guess they cannot be reversed. If, on the other hand, for example, they are on the right hand side for 1 and 2 and the left hand side for 3 and 4, that is to say the groves all face into the centre line of the carb bank, then the wrong slide could be in the body. Having never took one apart I can’t be sure if that is possible.
Don't know about blocked pilot jet, I did blast all Needle and Slow jets with compressed air (is the slow jet the pilot?), before re-assembly and air passed through those quite well in my amateur opinion.
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Hi, Eldrick. Unfortunately air blasting is no guarantee of a clear passage. I’ve discovered that much.
As for the slides, I’d whip the carbs off an have a peak. I cannot recall if the ‘pips’ are handed, thus allowing the slides to be incorrectly installed. Eg no1 in no 4. Sounds like you need to take them off to satisfy yourself. Could be 30 mins well invested?
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The amount of vacuum is not important as long as they are even, with regards to the slides adjust the height adjusters to the middle of their travel, then back off the tickover screw until iit s out of contact with operating lever, then check to see if slides are bottomed out, if bottomed out raise them using the tick over screw then bench set the heights evenly, then back off tickover screw until you can just about see light through carb throats, upon start up if tickover is racing back off idle screw, if this fails there is another problem , ie choke plates not fully open, ignition timing, air leak on engine side.
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Something lurking in my adled brain tells me that the carbs are "handed" so if you have a total box of bits(still got the 400 ones to do comfy, need felts) and you mix the slides up it is possible to get them in wrong. I may well be wrong on that myself, would be glad for confirmation
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Something lurking in my adled brain tells me that the carbs are "handed" so if you have a total box of bits(still got the 400 ones to do comfy, need felts) and you mix the slides up it is possible to get them in wrong. I may well be wrong on that myself, would be glad for confirmation
Then I am just going to remove the carbs from the block and look. The education alone from removing and replacing them gives me more confidence in doing my own maintenance
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There are two part numbers for the actual slider bodies so I'm guessing two on the left & two for the right.
If you look into the carb body from the air cleaner side you should see the raised curve of the rear skirt of the sliders if the air intake is off - you might need a small mirror or use a phone to photo it.
The front skirt is flat on the engine side.
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Currently stripped down and rebuilding all four of my Carbs.
No 1 and 2 carbs have guide pin for slides on the LEFT
No 3 and 4 carbs have guide pin for slides on the RIGHT.
This Carb numbering is as you look down from the riding position on the seat facing forwards, the slides as you look at them have a flat front and a slight curve at the rear,
When attached to the engine by the carb attachment bar, the curve of the slides are what you should see looking out at you, NOT the flat side.
When setting them up on a bench the distance from the FLAT side of the slide to the inlet Venturi should be 1.5 mm.
Is the emulsion tube where the needle jet fits and slides up and down fitted the right way up ? It should protrude into the Venturi a small way,looking like a small ‘cup’ if fitted upside down it will not be seen.
When dealing with multi cards ALWAYS keep them in separate labelled boxes to prevent them being fitted from one carb to another.
See how it goes.
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Is the emulsion tube where the needle jet fits and slides up and down fitted the right way up ? It should protrude into the Venturi a small way,looking like a small ‘cup’ if fitted upside down it will not be seen.
I will find out tomorrow when I take the carbs off the bike and I will have 4 boxes set aside for each individual carb should I deem it necessary to swap those slides.
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I would be surprised if the sliders are wrongly fitted as this would also cause problems on the top levered plungers unless they have been removed & put on back to front as well.
It will be interesting to see what you find.
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I would be surprised if the sliders are wrongly fitted as this would also cause problems on the top levered plungers unless they have been removed & put on back to front as well.
It will be interesting to see what you find.
I will photo-document it and if it proves to be 'an out of body experience' I will post the photos.If it is not the case, I may well get the idle and fast idle set knowing that it is me that needed expierience.
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Is the emulsion tube where the needle jet fits and slides up and down fitted the right way up ? It should protrude into the Venturi a small way,looking like a small ‘cup’ if fitted upside down it will not be seen.
I will find out tomorrow when I take the carbs off the bike and I will have 4 boxes set aside for each individual carb should I deem it necessary to swap those slides.
You do not need to take the carbs off to check - a mirror or phone will do the trick. You will see the curved part of the sliders - or not as the case maybe.
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Well, they are back to front so looks like I willl be learning a new task today, removing and replacing slides.
[attach=1]
[attach=2]
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Is it just two or all four?
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It’s hard to see on the photos, but if that’s 2 photos of cylinder 4, it looks to be correct. Eg cut out is on the inlet side?
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The carbs are obviously off. Those look very high to me if the actuator is in its static position!
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When I set my lifter heights I used the shank of a 3/16" drill bit using this video as a guide.
https://www.youtube.com/watch?v=JFTOfYl5BSc
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3/16” is good for the intake side, but I’d use 1/16” on the engine side.
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3/16” is good for the intake side, but I’d use 1/16” on the engine side.
You are right Philip I should have clarified that was on the intake side / air cleaner.
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Trouble with intake side you are guestimating you are on the same bit of the curve, thats why i use the flat side
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OK, I was wrong about the slides being back to front, what I have is a lack of knowledge as to what I am viewing and perhaps damaged slides.
I thought the gap everyone mentions was that little 'cut away' in my photo. Turns out that is just damage, all four slides have it so that led me to the wrong conclusion. That side is certainly the flat side. I suspect some clown has been jamming a drill bit in there... :P
I took the slides out or two bodies and behold, I saw the crescent moon, so, now I have filled gaps in my knowledge and I know my slides are correct. I did have trouble getting one to the base of the barrel so I just loosened everything. Discovered that the 'smiley face' butterfly things are all linked so I set them to look the same when closed.
Also found I could 'tighten my throttle cable' so to speak, using the nuts on the top near the throttle cable attachments. My throttle now does not have 20degrees of slack before it responds. I was able to rotate and lock the mechanism on the carbs using those nuts.
I adjusted the throttle stop too, so it stops when the slides are 1mm from the top of the barrel, the manual told me to do that. Pretty sure that part allowed me to get a slide to the bottom and ‘jam a drill bit in there’ after turning the tick over screw to raise it.
I put it all back together and started it up, have not took it for a run yet but I could get the bike to sit at 1200rpm. I will run it tomorrow and see if I can keep 1200rpm when the engine is at running temp, if not, when the engine is warm I will use the vacuum tune on it and see what I can get.
In the meantime, thanks for all the help.
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OK, I was wrong about the slides being back to front, what I have is a lack of knowledge as to what I am viewing and perhaps damaged slides.
I thought the gap everyone mentions was that little 'cut away' in my photo. Turns out that is just damage, all four slides have it so that led me to the wrong conclusion. That side is certainly the flat side. I suspect some clown has been jamming a drill bit in there... :P
I took the slides out or two bodies and behold, I saw the crescent moon, so, now I have filled gaps in my knowledge and I know my slides are correct. I did have trouble getting one to the base of the barrel so I just loosened everything. Discovered that the 'smiley face' butterfly things are all linked so I set them to look the same when closed.
Also found I could 'tighten my throttle cable' so to speak, using the nuts on the top near the throttle cable attachments. My throttle now does not have 20degrees of slack before it responds. I was able to rotate and lock the mechanism on the carbs using those nuts.
I adjusted the throttle stop too, so it stops when the slides are 1mm from the top of the barrel, the manual told me to do that. Pretty sure that part allowed me to get a slide to the bottom and ‘jam a drill bit in there’ after turning the tick over screw to raise it.
I put it all back together and started it up, have not took it for a run yet but I could get the bike to sit at 1200rpm. I will run it tomorrow and see if I can keep 1200rpm when the engine is at running temp, if not, when the engine is warm I will use the vacuum tune on it and see what I can get.
In the meantime, thanks for all the help.
Not convinced you are starting from the right point.
You mention damage, what damage not in your photo?
Damaged sliders will not be a meaningfull starting point.
You can't rely on them looking the same you need to start with all four sliders correctly set - did you watch the video link - that explains how you set them.
I found that you could close all four sliders completely by loosening the individual screws on the throttle links.
You can then start measuring the gap with a drill shank. If you fail to do this it will not run right on guesswork.
Once you have all four sliders correctly adjusted the large throttle stop screw will open them all by the correct equal amount.
It's not something you can rush if you are uncertaint what to do. Quite a few posts on here about how to set up the carbs.
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"Also found I could 'tighten my throttle cable' so to speak, using the nuts on the top near the throttle cable attachments. My throttle now does not have 20degrees of slack before it responds. I was able to rotate and lock the mechanism on the carbs using those nuts."
Unsure if I've got the understanding of that correct.
The twistgrip must have some degree of slack when setup properly, this to avoid the throttle being pulled when you turn the steering left & right. Too tight and the throttle will open as you go from centre to full turn, also it'll likely pull the nipple off the end of the cable without a certain amount of space to operate.
These are specified in the manual.
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"Jam a drill bit in there" is not what you do, you use the parallel shank part of a small drill bit as a feeler gauge
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🫣😣😳
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🫣🤔🥺
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😳😱😫🙄
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🤐
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Hang in there Eldrick. If you have got it running nicely at 1200rpm you must be doing something right. Keep at it.
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Unsure if I've got the understanding of that correct.
The twistgrip must have some degree of slack when setup properly, this to avoid the throttle being pulled when you turn the steering left & right. Too tight and the throttle will open as you go from centre to full turn, also it'll likely pull the nipple off the end of the cable without a certain amount of space to operate.
These are specified in the manual.
I do have some slack whereas before I had lots, as in very poor responce. A short run up and down the street tomorrow will let me know if it is not enough slack but it is certainly going to be better than the play I had before.
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"Jam a drill bit in there" is not what you do, you use the parallel shank part of a small drill bit as a feeler gauge
Understood, it was total sarcasm to follow from the previous statement I made in the same post, honest.
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Took photos of one of my carbs and the needle slide just to have them seen separately before I start reassembly.. as you can see the curve on the slider which should be facing away from the engine is clearly evident.
Inserting the slider and it completely drops to the bottom of the inlet tract as you would expect with a smooth action and no sticking.
Once fully assembled the adjustment to raise the sliders will be made and equalled out on bench, they will then be properly adjusted via 4 vacuum gauge so that all readouts are the same.
Not difficult just time consuming.
All my carbs are stored in separate boxes so no cross contamination occurs, before anyone points out the rusty bits they will be zinc plated and passivised before assembly.
Secret in dealing with multi cylinders and carbs is TAKE YOUR TIME and DONT RUSH., if in doubt consult the manual every time.
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Trouble with the manual is that it virtually tells you nothing. They don't appear to think anyone would ever take them apart.
Couple of pointers if you don't object.
You'll find Honda fitted screws that are in fact too short for the drilling, the carb tops are a perfect example. Most of the thread is left unused and corrosion of that thread left unused mean if you attempt to fit a longer screw if starts to grab and then strip away the thread. Clean the threads with a tap, measure how much thread is left unused and fit a longer screw, that why a lot of them strip out, they are only really gripping on a few threads. IIRC, the top screws are 16mm and you need 20mm, the float bowl screws are the same, look at the pic and you'll see the screws don't reach the top of the thread, the pressure of the spring washer tends to strip these threads out as only a few are getting used. If in doubt, fit longer screws and trim to suit the position. Don't have threads of the screw exposed as they corrode and when you try and remove them it can strip out the threads as it passes down them. Go for a flush finish.
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Ran the bike today and it all seems great, put the vacuum gauge on the carbs when I got home and I get this;
[attach=1]
#3 does show 10-15cmHg when I blip the throttle but otherwise, adjusting that slide just increases or decreases all the others by variable amounts.
Plugs are new, air flow upto the carbs is sealed so it could be a leak on the other side (the boots?). I did swap the vacuum tubes over to make sure that #3 tube and the carb tune wasn’t faulty. If it wasn’t for the vacuum gauge I just wouldn’t have known anything was wrong as the running response and idle seemed good. Well to my untrained mechanical brain anyway.
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Are all the exhaust headers the same temperature, ie, equally bloody hot when you've been riding?
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Are all the exhaust headers the same temperature, ie, equally bloody hot when you've been riding?
I will check the next time
Thanks
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No Vacuum to that cylinder, which means a massive loss somewhere. Check the valves on that cylinder, remove tappet covers and check they are first of all going up and down as the engine turns over. Either there's a valve stuck or the tappet is way too tight or there's a bent valve. Do a compression test if you can.
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Trouble with the manual is that it virtually tells you nothing. They don't appear to think anyone would ever take them apart.
Couple of pointers if you don't object.
You'll find Honda fitted screws that are in fact too short for the drilling, the carb tops are a perfect example. Most of the thread is left unused and corrosion of that thread left unused mean if you attempt to fit a longer screw if starts to grab and then strip away the thread. Clean the threads with a tap, measure how much thread is left unused and fit a longer screw, that why a lot of them strip out, they are only really gripping on a few threads. IIRC, the top screws are 16mm and you need 20mm, the float bowl screws are the same, look at the pic and you'll see the screws don't reach the top of the thread, the pressure of the spring washer tends to strip these threads out as only a few are getting used. If in doubt, fit longer screws and trim to suit the position. Don't have threads of the screw exposed as they corrode and when you try and remove them it can strip out the threads as it passes down them. Go for a flush finish.
No objection Ken,
Learnt a long time ago about Hondas plasticine screws, so all my screws bolts etc are stainless steel replacements, usually but not always hexagon headed cap screws. Again from experience I always use a tap to clean up the threads so I don’t get caught out with stripped threads..
Just got my BZP kit from Gateros so all the rusty bits you did see will be brought back to original look, a new venture for me but I enjoy doing something that poses a challenge.😀👍
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Ran the bike today and it all seems great, put the vacuum gauge on the carbs when I got home and I get this;
(Attachment Link)
#3 does show 10-15cmHg when I blip the throttle but otherwise, adjusting that slide just increases or decreases all the others by variable amounts.
Plugs are new, air flow upto the carbs is sealed so it could be a leak on the other side (the boots?). I did swap the vacuum tubes over to make sure that #3 tube and the carb tune wasn’t faulty. If it wasn’t for the vacuum gauge I just wouldn’t have known anything was wrong as the running response and idle seemed good. Well to my untrained mechanical brain anyway.
Is the bike running on all four cylinders or does it feel lumpy, as a 3 cylinder runner will sound ‘off’ and certainly will lack power. Do a quick check of the vacuum gauge by a light continual suck to see the mercury rises on each tube,
If all tubes rise and maintain their reading then you have discounted the gauge as a problem, if three falls as you maintain a suck then their is a fault in the gauge probably the rubber or it’s fixtures at either end.
Once you have ascertained if the gauge is faulty or not then proceed with the next step with engine running use a spray water bottle with soapy water and lightly spray the inlet tracts from carb to head, if there is an inlet leak the soapy water will stop it up for a short time and the gauge will rise, then fall which will prove or disprove this particular part as the problem, it has an ‘O’ ring seal which can flatten and leak, if the inlet rubber tract has a split then the soapy water will seal it but get dried out by the vacuum in a short time.
It’s all time consuming as is checking the inlet valve which in my opinion have closed up to almost zero mm to cause a vacuum drop.
Enjoy finding the fault
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Try swapping the vacuum tunes to make sure it’s not the instrument.If the bike is running as well as you mentioned earlier in the thread I doubt the issue can be catastrophic…
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One persons running well isn't always an accurate description unless you know exactly how it should feel.
Ted ran his 400 on 2 cylinders and even though he said it seemed to lack power he didn't spot it was only running on 2. Sorry Ted for bringing that back up but it's a good example.
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Not only that but it did some trips to Ashbourne on 2 cylinders! 😁
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One persons running well isn't always an accurate description unless you know exactly how it should feel.
Ted ran his 400 on 2 cylinders and even though he said it seemed to lack power he didn't spot it was only running on 2. Sorry Ted for bringing that back up but it's a good example.
True, I thought it was running great and sounding great, the vacuum gauge told me otherwise. I would have happily run the bike forever in ignorance otherwise. Now, I'm on a mission to fix it and expand my knowledge. ;D
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Hmmm! Tend to forget not everyone is a MotorVehicle Technician as easily back in the day. I did have my 400 run on 2 cylinders and noticed the performance drop off straightaway, cause was the yellow wire to the coil disconnecting.
Thank God Honda strap down Fuel Tanks with rubber which is quickly detachable, my BSA Bantam stopped on me one night 3 miles from home in the dark, pushed it all the way home to find next morning the bullet connector to the contact points had come apart, having a British bike kept you fit.
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Hmmm! Tend to forget not everyone is a MotorVehicle Technician as easily back in the day. I did have my 400 run on 2 cylinders and noticed the performance drop off straightaway, cause was the yellow wire to the coil disconnecting.
Thank God Honda strap down Fuel Tanks with rubber which is quickly detachable, my BSA Bantam stopped on me one night 3 miles from home in the dark, pushed it all the way home to find next morning the bullet connector to the contact points had come apart, having a British bike kept you fit.
In my defence I had never ridden the 400 before the rebuild - eventually the penny dropped with a combination of popping & banging - plus two cold exhuast pipes.
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Are all the exhaust headers the same temperature, ie, equally bloody hot when you've been riding?
No is the answer to that, 1, 2 and 4 are too hot to handle and 3 is hot but not nearly as hot as the others.
So, can't rule out spark plugs just because they are new, so I will swap plugs from 3 and 4 around and see what I get. Failing that as the problem is it 'just' going to be the HT lead or plug caps? I did re-set the gap on and clean the plugs when I took the carbs off. All plugs were a bit too dark but I expect that to change when I balance the carbs.
I guess it could be timing or valve clearance on #3 since I am quite sure the throttle slide does move freely as checked the play on them all when the carbs were off. All fore rise and fall when I engage the throttle manually and all the butterflies open and close too.
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update
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I just checked the plugs, #3 is still shiny and swapping it with #1 (which is black) made no difference. I then took the HT lead from #4 and connected that to #3, (no other leads are long enough to swap about) and #3 pipe got proper hot like it should.
I guess I need to do something with one or all of my HT leads then, but what?
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Once you have eliminated the Sparking you may have to look at fueling. If valve clearances are good then I would check the float level for the cooler cylinder.
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Once you have eliminated the Sparking you may have to look at fueling. If valve clearances are good then I would check the float level for the cooler cylinder.
I don't think I have eliminated the spark, I think #3 is sparking sporadically. Putting #4 HT lead on #3 made it spark (the down pipe was hot) properly. That does not meaan the coil is bad tho because #2 fires normally. I don't know enough about the wiring to #2 and #3 to safley say the coil is good or bad, I just think that the HT lead from the coil to #3 is at fault.
I suppose I could see if #3 lead will reach to #2 and see if it sparks there. if not, then I would be more certain that the lead or plug cap is at fault.
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Re. swapping the plug leads about, No 1 and No 4 share the same coil and points. Likewise, Not. 2 and 3 share the same coil and points. If you put the HT lead from 4 onto 3 it will spark on the wrong stroke. This also applies if you swap 1 and 2 over. Lift your petrol tank and check which leads are going to which plugs, plus to reassure yourself, make sure the low tension leads are connected correctly from the coils to the relevant points. You mention that when you put No. 4 lead onto No. 3 plug the exhaust then got hot. Is there a chance that it was incorrectly fitted in the first place? Have fun, it's a great hobby for keeping the old grey matter active. Mike.
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You mention that when you put No. 4 lead onto No. 3 plug the exhaust then got hot. Is there a chance that it was incorrectly fitted in the first place? Have fun, it's a great hobby for keeping the old grey matter active. Mike.
I don't think so, since the spark is is 'a redundant spark' I expected it to 'work' at the other end of the stroke to at least prove the fuel is getting through. So I think the leads aare all in the correct order. I just swapped them as a logical elimination step.
I will take the tank off again, tomorrow, and follow the leads to make sure they are #1and#4 and #2and#3.. If they aare not, then it needs new cables as they are not reaching anywhere else.
PS, I am having a good time doing this and learning.
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You mention that when you put No. 4 lead onto No. 3 plug the exhaust then got hot. Is there a chance that it was incorrectly fitted in the first place? Have fun, it's a great hobby for keeping the old grey matter active. Mike.
I don't think so, since the spark is is 'a redundant spark' I expected it to 'work' at the other end of the stroke to at least prove the fuel is getting through. So I think the leads aare all in the correct order. I just swapped them as a logical elimination step.
I will take the tank off again, tomorrow, and follow the leads to make sure they are #1and#4 and #2and#3.. If they aare not, then it needs new cables as they are not reaching anywhere else.
PS, I am having a good time doing this and learning.
if 3 out of four are heating up your leads are on correctly, valve time and ignition timing will be correct, I would look at valve clearances on suspect cylinder then do a leak down test, as well as swapping leads 2 and 3.
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If you are running on original coils I would certainly check where the lead comes out of the coil they seem to have issues there when the insulation rots separating from the central core. My 500 was very prone to misfire on one cylinder 1. When I fitted some inexpensive aftermarket coils it started immediately not much cranking needed as before.