I own a 1997 CBR 600F3, and it's been running weird lately. When I accelerate from a stop, or rev the throttle quickly when in neutral, the engine "stumbles" below 2500 rpm or so. Very easy to stall on takeoff. It runs very rough during this condition, but the instant it reaches the 2500 rpm range and above, it runs perfectly. Never had an issue above this rpm range, seems to make very good power and never stumbles. It does not matter what gear it is in, it could be in 1st or 4th, but if I ride the rear brake and load the engine below 2500 rpm, it runs rough still.

Side notes: I have replaced the air filter, fuel filter, spark plugs, wires, drained the fuel and replaced with the best octane fuel I could find (94 octane). Also, as far as I know the only aftermarket part it has is a Yoshimura silencer. The bike ran fine for 6 months after I bought it, and the pipe was on it for a couple years before that. I don't know if the previous owner had the bike re-jetted after the exhaust was installed.

Have any of you had this problem or something similar? I would appreciate any ideas, because it's getting annoying! (however still a blast to ride!)

 

What do you mean stumbles? Like almost falls flat on its face then sputters up to 2500 then takes off like a bat out of hell? I had a stumbling problem and it was my R/R...when the battery didn't have enough juice it would stumble if i didn't have the idle set at like 1700-2000

 

I have my idle set already at 2000, makes it easier not to stall at start-off. But yeah, anywhere below the 2500-3000 range, it falls on it's face, then takes off. Also, when I drained the fuel, cleaned everything, and re-fueled, it seemed to help for a little while, then back to the running problem...

 

are your carbs cleaned? if not...do it, clean the jets and make sure the floats and diaphram move smoothly

 

do what red said....if you still have the problem...give your battery a voltage test while the bike is running...you should see like 13-14v at 5000rpm