SOHC.co.uk Forums > CB350/400

Still carb troubles

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K2-K6:
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.

McCabe-Thiele (Ted):
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.

billdn:
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 🤞

royhall:
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.

billdn:

--- Quote from: Oddjob on September 04, 2023, 06:23:17 PM ---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 🤣
--- End quote ---

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