SOHC.co.uk Forums > CB500/550
500 four reluctant to rev
mickwinf:
All clear under there Bryan.
mickwinf:
been thinking a bit more about this and looking online for similar problems. when i first got it on the road i had trouble with the vent on the tank cap which is a repro. in normal running it seems fine and rode 25 miles no problem, but what if it is restricting air enough to stop it revving over 5000. problem is if i open the cap at speed fuel will spill all over. thoughts?
taysidedragon:
--- Quote from: mickwinf on June 22, 2026, 05:37:08 PM ---been thinking a bit more about this and looking online for similar problems. when i first got it on the road i had trouble with the vent on the tank cap which is a repro. in normal running it seems fine and rode 25 miles no problem, but what if it is restricting air enough to stop it revving over 5000. problem is if i open the cap at speed fuel will spill all over. thoughts?
--- End quote ---
When the bike won't rev over 5k, stop the bike somewhere safe and then open the fuel cap. If there is any air restriction you may hear the air rushing in. Wait long enough for fuel to fully fill the carb float bowls then close the fuel cap and try to rev the engine. If it still won't rev it's not a fuel cap issue.
Bryanj:
If it was the cap it will rev with it open or just after starting untill the tank has a partial vacuum.
Q will it rev in any gear over 5000 or never over 5000
Oddjob:
Just run the engine off a remote tank, that should isolate the tank vent question.
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