A Question for the XR600 Jetting Genius

I have a 1996 Honda XR600R which is dual sported. Before the bike was ever started I installed the HRC cam and an FMF supertrapp with 10 discs. The bike also has a higher flow twin-air foam filter. I was never able to get the bike to run right with this setup. No matter what jetting I used the bike had a lean stumble at idle which would kill the motor. Also the plug was a bright white showing a way to lean condition. I have owned a few other XRs and was always able to jet them. I eventually took the cam out and went back to the stock cam but still the bike ran lean and the plug was always white. I went as high as a 180 main to no avail. I even through the stock exhaust back on and no luck there either. I recently raised the needle one position (2nd from the bottom) and now the bike no longer stalls at Idle. Also the plug is running a lite tan color. Why was I not able to achieve this with jetting changes? I have completely disassembled the carb and soaked it in carb cleaner and blew through all the orifices. Could there be an ignition problem? Could my carb be faulty? My jetting now is 165 main 60 slow jet and stock needle set at 2nd grove from the bottom. I am still running the supertrapp with 10 discs. I know that four strokes come alive with correct jetting so anyone Please Help!! Has anyone experienced the white plug problem? My dealer said it is just California's fuel but I have three KTM four strokes and there plugs all run a dark brown. Mike :D:):D

Have you checked for an air leak? Maybe there's a hole or tear in the carb boot.

I have removed the intake boot and checked the o ring seal it was fine. I did not see any holes or tears in it either. Also I live and ride between sea level and 3500 feet.

Sorry to hear of your problem. Try starting bike and using starting fluid with the straw, lightly spray around intake manifold to see if engine rev's. This would indicate a leak. I have built 7 or 8 XR's, all with extensive mod's and have had intake leaks give your symptoms. I have a flatslide Mikuni, in excellent shape, I will let go for cheap. This is already jetted for mod's (bigbore, hi-comp.,cam, port-polish, header, exhaust,etc.) I jet a little fat...These gals don't like lean and will grenade. I also can include several jets. This was bought from Freddy at XR's only... I am sure he could give assistance also. Good luck!

Since the needle "blends" the different carb circuits together, it's position can have a dramatic effect from off idle to 3/4 throttle. A carb is not rejetted properly unless needle position is correct. I doubt there is anything wrong with your carb. It simply needed to be jetted richer, "across the board".

I agree with enduromaniac, I had the same problem with an FMF pipe on my XR600. I had to choke it all the time to start it hot or cold. I too raised the needle one notch and the bike ran great after that.

Mike

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