SOHC.co.uk Forums > CB750

F2 carb issues

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Harriec:
Hi...I recently joined and I'm having issues with my bike. I thought I'd start a new thread here as it's issues I'm having. I have narrowed it down to the carbs. The bike won't idle well. Once I've warmed it up with choke I can get it to idle around 1800 but any lower than that and it dies. If I do get it to settle well then after a few mins it will cut out and die. Also the throttle is not returning quickly. I've changed the cables and tonight I tried to sync the carbs. They were all about right (slight tweaks).  I can see that the PO has rebuilt them and there is definitely one big spring that's wrong and bodged (see pictures)

I think doing anything to these is beyond me. Does anyone have any idea who I could send them too?

I'm completely out of ideas on how to get it running better....

Laverda Dave:
You could try this guy, he's had good reports on the forum.

https://www.harpers-ultrasonic.com/about-harpers-ultrasonic

McCabe-Thiele (Ted):
I know nothing about your 750,  having read your first post you have had the bike for two years.
Going back two years has it ever run correctly?
Do you ride the bike regularly if not could your problems have started with old petrol or deterioration on the ignition/spark side?
You have mentioned spending about £600 at two different garages do you know what work they did?
Did the 750 run okay for a short period of time after the garage visits?

I ask these questions to try to understand what aspects you have been able to rule out 100% before concluding  the carbs are the problem.  You could have the carbs refurbished only to find out that even with a wonky spring they are not the problem.

What is your level of ability to work on the bike is it sufficient to definitely rule out the ignition/timing side?
Are the compressions good?
Are there air leaks anywhere on the induction side?
Is the advance & retard working as it should - could the mechanism be partially seized so the revs do not drop as the timing is too advanced?
Was the valve timing set up correctly by the PO?

For the engine to run at high revs with the throttle closed how is the fuel & air managing to reach the engine?

Bryanj:
PD carbs are notorious for clogging and need complete and thourough cleaning by somebody who understands them, i wont touch them at all

McCabe-Thiele (Ted):

--- Quote from: Bryanj on April 01, 2024, 11:29:55 PM ---PD carbs are notorious for clogging and need complete and thourough cleaning by somebody who understands them, i wont touch them at all

--- End quote ---

Are there later carbs available that will fit to replace the PD carbs Bryan - they must be bad for you not to touch them?

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