Honda-SOHC
SOHC.co.uk Forums => CB350/400 => Topic started by: billdn on September 04, 2023, 06:15:31 PM
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Back in February I posted saying I think I'd sorted my troubles with carbs not shutting down . In April I went for a Boyer electronic ignition complete with micro coils and I still have the same problem with the carbs !
There's quite a long time between posts because my wife was very ill with lung cancer and sadly passed on 30th June , so shed time was the last thing on my mind!
However one of her last wishes was "Get that bl##dy bike sorted!" So I'm now back in the mood to try and sort it.
From the top :-
Boyer fitted and bike starts/runs. Using a timing light its correct.
Tappets adjusted.
Have to fiddle with idle adjuster to set at 1200rpm .
Idle mixture screw set at 2 turns out.
Plugs very sooty
Open throttle and revs soar and doesn't drop back to 1200rpm when released. Have to fiddle with idle adjuster to bring back down.
Sprayed carb manifold connectors to barrels with Carb cleaner and no effect , so not drawing in air, better not they're new - good
Remove carb tops and sprayed carb cleaner in but slides don't appear to be sticking either.
I've noticed that if you press the top of brass hexagonal nut on the carbs this will reduce the revs but too hard and it stalls FWIW.
Prior all carbs stripped, ultrasonic cleaned, carb cleaner on jets with jet brushes etc etc retaining original brass and new seals from NJ.
Bench synced at least twice.
Standard air box and new air filter
I've no idea what to do next! I have an old lawn mower, never serviced, starts first time every spring, think I'll put engine from that in instead.
To me it's pretty obviously carb related, (I think ::)) as there is good spark and timing is ok. Not got to the stage with setting Boyer to full advance yet which requires 4500rpm as revs all over the place.
Cheers peeps! 8)
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So very sorry to hear of your loss Bill 😢😢😢
Also so sorry to hear you're still battling the carb gremlins 😁😁😁😁
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Very sorry to hear about the wife.
You could try this as to me it sounds as though the throttle lifters are set too high, especially if the carbs have been apart.
Get the adjuster screws, the ones with the little 8mm headed nuts on and the flat bladed screwdriver slot. Screw them all down as far as they can go. You may now struggle to get the bike to tickover and starting will involve a little jiggling with the throttle. Once you get it started adjust the main tickover screw to see if it will idle. If so, now vac the carbs to equalise them.
See if that works.
Before you do that post a pic of the adjusters so we can see how high they are now.
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Bill, sorry to hear about your wife......
As Ken says, the adjusting of the lifters can have a remarkable affect on the tickover and settling back to idle.
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Sorry for your loss Bill.
That sounds to me like the quadrant is not positioned correctly when it was reassembled. Got the tee shirt for that one, took me ages to find it but the symptoms were as described above. Repositioned things correctly and it was spot on. Unfortunately the old memory won't allow me to remember how I fixed it but someone will know.
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Sorry again to hear about Rose, good to read you are taking her advice & cracking on with the 400.
Can't remember without trawling through your old posts if you did a bench sync or not.
It was beginners luck with my 400 as I did the bench sync after rebuilding the carbs I think it's called to get all the sliders equal iirc I used a 1/8" drill bit shaft to get them all the same.
The below links I found very handy as well as the video & tips here.
.https://www.vintagebikebuilder.com/cb350-400f-carb-rebuild-demonstration.html
https://www.youtube.com/watch?v=JFTOfYl5BSc
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Can't help with the carbs Bill but so sorry to hear about your loss and hope you get her wish sorted!
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So sorry to hear of your loss.
But heartened to hear you are pressing on with getting the 400 sorted.
If the advice above doesn't work my similar problems were sorted when I got the correct brass in all the carbs.
Best wishes
Tim
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Bill, sounds like the bench sync wasnt quite right, i had the same problem with the 400 carb jigsaw i had for a member on here, what Ken suggested is a good idea, if you can get them off, undo the tickover screw all the way then unadjust all yhe little adjusters till you are certain all the slides bottom out, pick one to use as set point and lock small adjuster then using big tickover screw adjust till smallest, undamaged, drill shank, idealy 1mm, just slides under flat side of throttle slide(engine side) the adjust all small adjusters so all slides are same using the drill as a feeler gauge.
If you had them totally apart check you havent mixed the slides up as they are handed and you would not be the first to make that mistake mate.
Condolances on your wife and we will do all we can to get that *^##*^bike sorted
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Sorry for your loss Bill.
That sounds to me like the quadrant is not positioned correctly when it was reassembled. Got the tee shirt for that one, took me ages to find it but the symptoms were as described above. Repositioned things correctly and it was spot on. Unfortunately the old memory won't allow me to remember how I fixed it but someone will know.
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Thanks Roy,
Not sure what you mean by the quadrant ? Do you mean the part the the push/pull throttle cables connect to? not sure how that could be misaligned but every day is a school day with this.
Cheers
Bill
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Thanks all for the thoughts and support, it's been a rough road .
but inwards and onwards!
I'll try Ken's suggestion first and then if needs be, and fear it will , I'll take off the carbs, again and do yet another bench sync. The guy on the production line building the 400 must have loved his job of fitting the carbs !
Might be a day or two as got to help the oldies (parents) for a few days after today.
But as Arnie says "I'll be back"
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So sorry for your loss too Bill! But power to your elbow for stepping out the other side and getting on with things! Good to have a focus and distraction. Good luck with the running issues.
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I will go back and check my 350F build thread when I get a chance. My carbs came ready built from Gerben in Holland and came with the quadrant problem. He sent me an email of how to rectify it so will look for that as well. Yes the quadrant is where the push and pull cables connect. Is your pull cable only just fitting or is there plenty of adjustment.
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Very sorry to hear about the wife.
You could try this as to me it sounds as though the throttle lifters are set too high, especially if the carbs have been apart.
Get the adjuster screws, the ones with the little 8mm headed nuts on and the flat bladed screwdriver slot. Screw them all down as far as they can go. You may now struggle to get the bike to tickover and starting will involve a little jiggling with the throttle. Once you get it started adjust the main tickover screw to see if it will idle. If so, now vac the carbs to equalise them.
See if that works.
Before you do that post a pic of the adjusters so we can see how high they are now.
Pics of adjusters prior too screwing in , hopefully attached
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I will go back and check my 350F build thread when I get a chance. My carbs came ready built from Gerben in Holland and came with the quadrant problem. He sent me an email of how to rectify it so will look for that as well. Yes the quadrant is where the push and pull cables connect. Is your pull cable only just fitting or is there plenty of adjustment.
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Cables fine Roy, plenty of adjustment on both, which I think is good 😏
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If you want another "pair of eyes" to help out with it Bill, I could have a day walkabout to see if we can get our heads around it together.
Which area are you located in West Sussex ?
Offer on the table should you need it.
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Trying to think outside the box here it smacks of running too rich so engine does not want to throttle back so as to speak- sorry to question you about the obvious - are you running on the original needles, emulsion tubes, jets , etc- middle position with the circlip on the needle? Float levels all correct?
I'm sure you will have checked but is the throttle mechanism closing okay with no chance of a cable bind anywhere,
is the choke mechanism for the fast idle going off with the choke?
If all of the above are good it has to be getting the bench sync sorted imho.
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Thanks Ted but all of the above is correct, original brass and kept circlip in correct position. Hope by end of day will have tried screwing down slides and vac gauge 🤞
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Bill. I had a look for the old emails to Gerben in Holland who rebuilt the carbs and this was the conversation at the time. I don't know if it relates to your scenario but my symptoms were very similar to yours. The outcome was that I took the carbs off and returned them to Gerben at his request as it was a rebuild error so I didn't actually fix the problem myself. Anyway, this was the email conversation.
Hi Gerben. Carbs arrived okay a few days ago. Tried them on the bike today and the tick over is at 3000 rpm with the throttle stop wound right out. How do I turn down the tick over?
Hi Roy, what do you mean with the tick over? I do not know this term. Please describe what happens.
Sorry Gerben probably an English term. I’m referring to idle speed. Cheers.
Roy, okay I think I understand. There is an adjusting screw with an M8 nut near the number 1 carb. It is used to open the slides a little bit when you have the choke closed for cold start. Just loosen the M8 nut and screw back the adjusting screw. Then try again to run the engine. When the screw is backed off a little you can adjust the idle speed using the normal idle screw. If the engine is running okay you can screw back the choke adjusting screw that far that it just doesn’t touch the aluminium actuator then fasten the M8 nut. When you actuated the choke now you will see the slides open a little bit.
Please let me know if this solves your problem.
Out of curiosity I just had a quick look. The adjuster you refer to has got a small gap between adjuster and striker plate. With the idle adjuster backed right off the throttle slides are still too high. Can I drop them slightly using the four adjusters near the brass caps?
Yes Roy that's also possible. The only thing you have to watch for is that they all 4 lower the same amount otherwise the engine will run very uneven.
Of course you have to use a vacuum set for final tuning but in the first place you can try to lower the slides a little bit.
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Very sorry to hear about the wife.
You could try this as to me it sounds as though the throttle lifters are set too high, especially if the carbs have been apart.
Get the adjuster screws, the ones with the little 8mm headed nuts on and the flat bladed screwdriver slot. Screw them all down as far as they can go. You may now struggle to get the bike to tickover and starting will involve a little jiggling with the throttle. Once you get it started adjust the main tickover screw to see if it will idle. If so, now vac the carbs to equalise them.
See if that works.
Before you do that post a pic of the adjusters so we can see how high they are now.
Hi Oddjob,
Just tried above and got it sort of running with enough revs to attempt Carbtune. Oddly #2 tube to carbtune kept blowing off the adaptor. It was helping and adjustment could be made but soon as pipe blew off engine stalled.
Looks like a bench sync coming up 😏. Also#1 exhaust pipe was nowhere near as hot as the other three, although still hot to a degree. And yes did check carbtune pipes were on correct carb 🤣
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That's concerning regarding the pipe blowing off the adapter. Does it sound like it's popping back down the carbs?
Don't do a bench sync if you have gauges, Number 1 pipe not being hot could be low float height or that carbs throttle slide is so low it's not getting enough fuel.
Did you manage to get the gauges to level or did you stop when the engine stopped? Maybe try winding number 1 adjuster half a turn upwards.
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Just tried again, wound #1 slider out a bit. Started but #1 bar doesn't even show on scale ,#2 rises a bit as adjusting the others. #3 bar shot to the top and #2 pipe popped off again with a distinctive pop sound but doesn't sound like a backfire. 3 and 4 nearly achieve adjustment but 2 and 1 not having it.
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If you have a compression gauge I'd test the cylinders. Especially number 2
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No don't have one, probably could borrow one. The engine has been rebuilt from bottom up, rebore, new pistons, rings, timing chain, primary chain, valves etc surely shouldn't be compression problem.
You've far more experience than me so not saying your wrong, if so what's caused/causing it?
Before I switched to the Boyer I did get a good balance onbtge carbs but still wouldn't shut down when approaching giveaways etc.
Took them off, bench sync again , refitted added Boyer and now still same problem. Driving me 🤪.
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If you want another "pair of eyes" to help out with it Bill, I could have a day walkabout to see if we can get our heads around it together.
Which area are you located in West Sussex ?
Offer on the table should you need it.
Cheers gave sent you PM 👍