Motorcycle Repair: bike wont go above 5000 rpm, honda cb350, vent holes

Question
i have a honda cb350 i got from my brother last summer. i got it running near the begginning of the summer, but it's been very tempormental. there's only been one full day where it's ran perfectly. so i've constantly been adjusting points and timing, i've cleaned the carbs and rebuilt them and everything else i can think of. it stopped working for a while (i think it kept flooding the engine) and i just got it running this morning. when i took it out for a spin the engine with or without a load wouldn't go above 5000 rpm. any idea whats going on here?
Thanks

Answer
Nick, most of the issues about a failure to rev past that kind of rpms are either bad diaphragms in the carb tops or the spark advancer is stuck.

If you have been through the carbs and everything is clean and the diaphragms are good, then I guess you can look to the ignition timing issues.

Remove the point plate, check the mechanical advancer for proper advance/retard function. Clean the points and reset the gap to .012-.014" then set them to open on the F and LF marks by moving the plate and/or doing slight point gap adjustments to change the timing.

Watch the points with the engine running and look for excessive arcing across the point faces. If this is the case, then you have a loose or bad condenser. Be sure that the condenser set is well grounded to the frame and the leads are all clean and tight. Look for any place where the leads could ground out against the fuel tank or frame.

Check the spark plug caps for excessive resistance.. should be around 5k ohms or less and both should be close to the same values.

Use a fresh set of B8ES plugs once you have checked everything else above. Plugs can get fuel/oil fouled easily and a fresh set will eliminate that issue.

Make sure that the fuel flow to the carbs is good. Tank, petcock, lines should all be clear. Be sure that the gas cap vent holes are open.

The battery must be fully charged and charging system operating properly. This is a battery powered ignition, so once the volts drop below about 10, then you will start having a lot of running problems.

Bill Silver