My engine is running poorly

My engine lacks power under throttle load.

Make sure there's nothing covering the openings to the airbox under the seat. One time I had some maps in a zip-lock bag under the seat. It was cutting out at full-throttle and I couldn't figure out why...well, guess what..that zip-lock bag was over the two holes in the airbox and every time I opened it up the vacuum was sucking the bag down on the airbox and whamo - no air!

Also check:

• Is your choke cable/mechanism working properly on your carbs? The choke may be stuck on.
• Are both spark plugs getting good fire?
• Are your valves adjusted properly?
• Are your carbs synced?
• Have your carbs been cleaned in the past several years?

My engine is backfiring.

If the engine is just popping a little bit as you decelerate, then you're getting preignition. This is caused by a lean mixture condition. Check carbs for vacuum leaks, or richen (raise) the needles or idle mixture (turn out screws).

If the bike is seriously backfiring, then you might still have a lean condition, or maybe even a rich condition (check your choke). This is because a lean mixture can make the engine miss, then the unburnt gasses are ignited in the exhaust pipe on the next cycle; a rich mixture can have the same effect since unburned fuel will also be present...

Check pilot circuits in the carbs, change the spark plugs (make sure to gap them properly), check for exhaust leaks. If all else fails, try a higher octane fuel.

My bike will run for a while, but keeps losing power and dying when I ride it.

This indicates tight valves. It dies at low RPMs, but will continue to run if the throttle is opened.

Take the bike in and have the valves adjusted (or do it yourself) before you do real damage to the motor.