SOHC.co.uk Forums > CB750

F1 lumpy low speed running.

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Skoti:
Sorry to keep posting as many questions, but this is the first F1 I've owned and I'm not sure what to expect of it.

At low speeds and around 2000rpm when riding through towns the motor feels lumpy, open the throttle a touch and it becomes smooth.

Is this normal   :-\

 

Bryanj:
No probably needs carb balance but do all the rest of the service items FIRST

Skoti:
Hi,

Yes has had new plugs and points fitted.
 
Timing done with strobe light.
 
Carbs removed and cleaned out and balanced with mercury gauges.

Valve clearances and cam chain adjusted.

New after market air filter fitted.
 
Air screws adjusted to 1 3/4 turns out.
 
Idles at 1000rpm when hot.

Only on very light load and small throttle openings the motor is lumpy and erratic.

I notice that spark plugs No 1 and 3 are a little sooty compared to spark plugs No 2 and 4. Do you think I should turn the air screws out a bit more on carbs No 1 and 3 and see what happens?  :-\

Spitfire:
Mine is not impressed at slow running so I just go down a gear or two, works OK then.

Cheers

Den

BigAl (Alan):
I would go back to balancing the carbs again, well worth investing in a kit. I had similar problems with my CB750 but it did sort out the low rev lumpy/chain snatch problem

Good luck

Alan

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