Motorcycle Repair: 71 CT90 FUEL PROBLEM, point gap, ct90

Question
MY CT90 RUNS GOOD AT LOW SPEED HOWEVER ON HILLS OR WHEN OVER 3/4 TROTTLE FOR ANY PERIOD OF TIME, IT JUST PULLS DOWN AS IF IT IS NOT GETTING FUEL.  I HAVE CLEANED THE TANK (RUST POWDER WAS IN IT), CLEANED SCREEN IN PETCOCK, REBUILT THE CARB AND ADDED AFTERMARKET FUEL FILTER.  DOES THIS SOUND LIKE A MAIN JET PROBLEM TO YOU?  ONE OTHER THING THE MUFFLER IS SOMEWHAT RUSTED OUT.

Answer
Dan, be sure that the fuel cap is venting properly. If you used an aftermarket carb kit like KEYSTER, the calibration may be off. Running the bike with a other than OEM stock backpressure muffler condition can cause jetting issues. Be sure that the valves are adjusted to .002" that the spark advancer is functioning properly and that the point gap is correct and ignition timing is also set to the F mark alignment on the flywheel/stator marks.

If the bike has low compression due to worn rings or old piston seizures, then it needs to be freshened back up to original specifications before you can do much tuning or troubleshooting.

Bill Silver