Yamaha Grizzly Misses When Put On A Load

[flagcar]

My 2003 Grizzly 660 recently started puking on me. I was riding in some pretty muddy terrain and everytime I hit a deep mudhole, it would start missing. I figured water in the carb, but it was dry everytime I checked. I brought it home, tore it apart, changed the plug, cleaned the air filter, and put dielectric grease in all the electrical connections. No help. When I open the throttle it doesn't rev up as fast as it should. I took it down the road twice: the first time it started missing everytime i held it wide open. The second time it didn't miss, but had a noticeable power loss. Please help. I am getting passed in the woods by 300cc Quads!!

[SimpleMan]

I'm no expert on Grizz but check your fuel. You might have water mixed in with the gas.

Also check your battery

[rpyfz450]

You could have a flashover condition where the spark is jumping to ground somewhere. I've diagnosed this problem in the past by observing the engine in pitch dark while revving it. A friend of mine showed me that if you spray down the spark plug leads with WD40 or other types of oil, it will sometimes solve the problem.

I've also had similiar symptoms caused by a bad ignition coil. The ignition coil passed the static test in the service manual, but replacing it solved the problem.