SOHC.co.uk Forums > CB500/550

flat spot

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mickwinf:
story so far, 500 four 1974, rebuilt and on the road. I have an issue with a flat spot as I pull away from a standstill or low speed, it hesitates badly unless I give it lots of revs, sometimes even cuts out. carbs have been cleaned and new gaskets and o rings, all jets clear and correct numbers. Timing has been checked, valves are correct gap, new clean petrol. otherwise it runs well, over 3000 revs it goes very well, goes better when colder, worse when hot. I have synchronised the carbs and tried the air screws at various settings from half a turn to two turns out. standard aircleaner with new filter. no air leaks.So where do I go next, should I try changing the needle settings?

hairygit:
Float levels would be my first thought to check. Does it start from cold without choke? Do you get sooty looking plugs? Any sign of dribbling from the overflow tubes? Any of those would make me suspicious of float levels or float valve leaksge, especially as it gets worse with the engine warm/hot

mickwinf:
float levels have been set using special tool, no leaks, plugs are slightly sooty so I suspect its a bit rich, it does tick over ok but when the throttle is opened it hesitates or cuts out.

Bitsa (Ralph Wright - RIP):
Defiantly rich
Cheers
Bitsa

mickwinf:
I agree but adjustment of air screws does not improve it, should I be looking at needle position?

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