Total Motorcycle Community Forums

I am in the process of bringing an old 1980 Yamaha Maxim 650 back to life. I have cleaned and rebuilt the the carbs and it started and ran pretty good until tonight. I now has the following problems:

1. Bike will not start. Turns over, pops a couple of times on choke but nothing more than a second.

2. While starting, a really loud backfire occurs every once in a while with flame coming out the tailpipe.

3. Spark plugs are not clean dry and they are less than a month old. Pulled them out, cleaned and gapped accordingly. Seem to catch a little better but would eventuly get wet and black again.

4. I think there might be some issues with carb 3 which is where the vacuum hose for the petcock comes from. It also looks like there is no fuel in the bowl (opened the screw and nothing came out).

Carb boots have been replaced, all new fuel lines and petcock rebuilt. I did pull the petcock and check the fileter but it looked fine.

Any ideas from anybody? Neighbor thinks I am shooting a gun everytime it backfires.

I had almost the exact same problem with my maxim 750, unfortunatly a cam chain guide broke inside the engine, the cam chain jumped a tooth or two or ten. And the timing being off made it do exactly what you are describing. I took the oil pan off of mine, wich requires takin off the exhuast, and noticed little chunks of plastic. Hopefully this is not your problem. I might try draining the oil a looking closely to see if there is anything unusual in there.

Update:

Put new plugs in and adjusted the idle. Now runs great.