Run away high idle
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Run away high idle
Hello everyone, I am really hoping someone has a solution for this issue. I am rebuilding a 1999 cbr600f4 and I am having trouble finding and fixing the cause of a runaway idle. I replaced the engine with a used one from the same year (it may be a different model than the us/canada now that I think of it but I will check the engine number if this matters) and now idle runs away up to 3000-5000 rpm very shortly after starting and every time I run it.
Here is much of the relevant info: Adjusting idle screw down doesn’t solve the problem because then it doesn’t want to keep running (idle wasn’t adjusted high anyway) and the carbs are not way out of sync and the pilot screws are 2and3/4 turns open. Throttle was not stuck open.
I have checked and sealed all vacuum lines. That didn’t work, then I deleted the Pair system and that didn’t change anything, then I deleted all the aircut valves on the carbs because one was faulty (I plugged the vac line into them and the vac source for them from the carb) and this didn’t change the idle issue.
I’ve cleaned the carbs, replaced the seals except the diaphragms looked fine, kept all the stock jets, and choke valves are not sticking or clogged. Floats are good and float needles not damaged. All carb passages were clear when I reassembled. Engine Intake boots were replaced for good seal.
I can easily check valve clearances, timing and pulse generator. However I hope it’s not the computer, and head gasket. Has anyone had so much trouble with this? Or is there a mechanical genius who can help me diagnose?
I really want to save this bike Please and Thank you!
Here is much of the relevant info: Adjusting idle screw down doesn’t solve the problem because then it doesn’t want to keep running (idle wasn’t adjusted high anyway) and the carbs are not way out of sync and the pilot screws are 2and3/4 turns open. Throttle was not stuck open.
I have checked and sealed all vacuum lines. That didn’t work, then I deleted the Pair system and that didn’t change anything, then I deleted all the aircut valves on the carbs because one was faulty (I plugged the vac line into them and the vac source for them from the carb) and this didn’t change the idle issue.
I’ve cleaned the carbs, replaced the seals except the diaphragms looked fine, kept all the stock jets, and choke valves are not sticking or clogged. Floats are good and float needles not damaged. All carb passages were clear when I reassembled. Engine Intake boots were replaced for good seal.
I can easily check valve clearances, timing and pulse generator. However I hope it’s not the computer, and head gasket. Has anyone had so much trouble with this? Or is there a mechanical genius who can help me diagnose?
I really want to save this bike Please and Thank you!
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Joined: Mar 2013
Posts: 7,170
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From: Alabama
Are you sure the idle adjustment screw is connected to the carbs? Unfortunately, there isn't a stop on it to keep it from unscrewing all the way.
I'm not sure that's your issue, but it should have affected idle when adjusted.
I'm not sure that's your issue, but it should have affected idle when adjusted.
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