[ZoA]

I own a 2005 CRF450x I've turn it into a street legal motorcycle and lately I have been having some problems with it. In all 5 gears when the bike starts reeving up to around 3-4000 rpm the bike stutters back and forth. This only happens when the bike is moving not sitting still for some reason. I feel like it is a carburetor problem where the bike isn't getting enough fuel. The bike does have an aftermarket exhaust on it.

I've tried changing the jetting
I Changed the spark plug
Cleaned the carburetor
Tightened the chain.

Please if anyone thinks they know anything please, help me out!

 

[Dodsfall]

I would check to see if the float level is to spec as a first step. Was the carb disassembled and soaked in a dip or ultrasonic cleaner? Were the jets gone through with cleaning wire to make sure they are open?

 

[Critter]

Gas tank vent?

 

[Nigall]

One reason that it doesn't misfire when stationary could be that at that time, the engine is not under load. That would suggest to me there is a compression problem that comes to bear when the engine has to work against the riding load. Just a thought, but non-spec exhausts can cause hot spots that burn away the valve seatings. Sorry to be the bearer of bad news...

 

[hogcowboy]

I'm not familiar with that bike but in general, if the stock air filter has been changed and sometimes the muffler(s) some bikes could need some kind of tuner to change the timing or other parameters. Being a carbed bike, is there a need to sync the carbs if there are multiple? And as Critter suggests, open the fuel cap the next time and see what happens.