My 82 yamaha xs400rj starts and idles perfectly. It runs and pulls up to 5000 rpm perfectly.
http://home.comcast.net/~panofish/WEBLO ... index.html
If I push it beyond 6000 rpm ... the engine hesitates randomly (as if it is misfiring or fuel trouble).
What I have done so far...
I checked the petcock.
Replaced the spark plugs.
The right spark cap is 8.5k and the left cap is 11.8k.
The coils measured identically and withing specs.
Spark plug wires are good.
The left spark plug looked super clean ... the right plug had some black sooting.. http://home.comcast.net/~panofish/plugs.jpg
I swapped the coils and the caps and the bike ran the same and the plugs appeared the same.
I checked and cleaned the fuel cap vent holes.
I have thoroughly cleaned the dual carbs twice, I'm meticulous, but not an expert, so I could have missed something.
Fresh tank of gas and a long ride made no improvement.
My best guess is that everything points to the right carb as being to rich?
Is this a good guess? How can I lean it out a little to test?
Any other ideas and suggestions would be greatly appreciated.