Topic: Bike over revving after 2 minutes of running

[rogertommy]

Hi I have recently bought Honda CB 550 four, I was told there was a problem with the carbs but I liked it and bought it anyway, we have stripped down and cleaned everything,replaced carbs ,then started her up,ticking over lovely. Then after 2 mins revs go to 3000 and only way to stop revving is to shut it off. Took all off and checked ,replaced and still does the same,can anyone help me please?

[Johnie]

Did you find and turn down the idle screw? If so, then it sounds like the slides in the carbs are set to high. Need to adjust those so they close down further. Did you do a carb sync? What year is that bike?

[rogertommy]

Hi it's 1977 can you explain bit more please? How can you get slides to drop as they are already on the bottom,when it's revving up I pushed on slides and they are right down?


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[Johnie]

Are you sure the throttle cable is not holding anything up? Pretty soon a 550 guy will chime in for you. On my 750's there is an adjustment that is used to sync each carb by getting all the slides in the same position. It may feel like the slides are down, but if one is up a bit it can cause a fast idle.

[Parkwood60]

If the slides are down and it still revs it sounds like an air leak. Could have a cracked rubber between the carbs and the head, could have a loose screw in a carb itself, could even have a crack somewhere in the carb itself.  You say you replaced the carbs, what with? Another set of unknown 40 year old CB550 carbs? Or did they come off a bike that recently ran perfectly?

A lean mixture will cause RPMs to run up like that. Could be an air leak, could also just be a clogged idle jet passage, or slow jet not letting the motor get enough fuel.

[SteveD CB500F]

Roger - pop in to www.sohc.co.uk and chat to the UK mob. There's bound to be someone close.

Use the same username so that we recognise you!

Steve

PS: Is your '77 an F or a K3? My K3 revved like that if I left the choke on after the first few minutes. There's a throttle lifter as part of the choke mechanism which may be stuck.