OK..have had a few rides between the cold snaps up here in the north east.. seams that when I shift ,up that is . I get a backfire out the carb. other than that it runs fine... I did not run the bike when I got it so I dont know if this was a problem before the build... I have an original Zenith carb with a forcewinder air filter attached. I was getting rough coughing and spitting at high rpms, so I started to screw with the highend adjustment..started at three turns out ,no good so I went back in (clockwise) 3/4 of a turn and seems to do just fine at high rpms. I do have alot more air intake than stock with the forcewinder. so Im looking for some info on the back fire out the carb??? thank Rick

 

Backfiring out the carb may be caused by the ignition timing being off.
Another reason may be because the engine has not warmed up yet.
If it backfires when the engine is at operating temp, then strike that.

Check the points gap on both ignition cams. They should have a gap distance of within .004 difference at most. A greater distance than that will affect the ignition timing to a slight extent. More importantly, it reflects a possible worn ignition cam that needs replacing......... pg

 

I will check the points gap, thanks, RJ

 

This is a magneto, can the cam be warn even with having the bakelite points arm?? and I put brand new points in there about 200 mi. ago.. But your right I didnt check between the high and the low parts of the cam.. didnt know it was necessary. and I didnt check timing with a light ,just with the timing hash mark and with both valves closed and .001 clearance at points just before cam was high centered

 

Could be an air leak, or running lean.