SOHC.co.uk Forums > CB350/400
The elusive surge
K2-K6:
Its this proceedure referred to above http://www.sohc.co.uk/index.php/topic,17769.0.html have you worked in this sequence as it deals with exactly the problem you describe ?
Effectively, it resets the initial relationship between the slide position in the carb venturi and where the main idle speed adjust screw interacts with the throttle lift system components.
If the two conflict, then you'll never get it to run consistently.
Alexrayz:
I did indeed! Even found an actuall drill bit that is 0.15mm (1/8")
Bryanj:
1/8 inch is 3mm not 0.15mm
Alexrayz:
--- Quote from: Bryanj on January 17, 2022, 02:59:14 PM ---1/8 inch is 3mm not 0.15mm
--- End quote ---
Right. 1/16" then. Still not accustomed to imperial measurements, but it was 0.15mm thick measured on the engine side.
K2-K6:
--- Quote from: Alexrayz on January 17, 2022, 02:50:36 PM ---I did indeed! Even found an actuall drill bit that is 0.15mm (1/8")
--- End quote ---
Apologies for labouring this point, but it's fundamental to identifying why you are having difficulty. If you complete this successfully you should be able to wind the "idle" screw down far enough for there to be no real gap under the slides when you look through the carburettor, this is correct and should be able to effectively almost stall the engine when it's running.
It's then important that you leave them alone (don't now synchronise with guages) to further assess the problem. This effectively separates different causes to let you find the real problem.
Then start the engine when reassembled for 20 seconds and switch off. Now check to see if all cylinders have hot exhaust which would indicate they all fire straight away. Any cold pipes and you'll need to find why that cylinder is not firing. All ok ? Move to next check.
Then, with it running, complete a spray test on inlet tracts to see if the engine speed alters (spray wd40 or similar around carb to head rubbers) this should not change the engine speed, but if it does it will confirm there's a leak somewhere that is allowing air to enter the engine after the throttle slides which are supposed to be the only control.
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