my 800 has 1150 miles,one day after riding i went to start it and had huge problems,it seemed like it would fire on one cylinder then stall.everything cleared up, 2 weeks after same starting prob then runs fine after.1 week later starts nice but serious lack in power and engine knocking noise. I'm hoping this sounds familiar and is an easy fix.any feedback appreciated

 

Sounds like what a short in the T-bap wiring or connector would cause. Intermittent, will run ok,then will run crappy. Repair Kit #2875542 BUT unless they have improved it, will have the same thin wiring. First thing I can think of that happened the most. Plus water in fuel could have similar effects?? OPT

 

This might be a long shot, but here is what happened to my 500 efi. It had similar symptoms to yours before it failed entirely.

The sprocket on the crankshaft that drives the chain for the overhead cam had broken. It was still in place enough so that the chain and cam turned, but the chain had skipped several teeth - which put the valve timining off.

If you have this problem, you will be able to see that the valve timing is off (pretty easy to check) and will probably have reduced compression.

The fix is not as bad as it sounds. I could get to the sprocket and the nut that retains it by simply taking the side cover off, pulling the flywheel, removing the stator. You also need to take off the rocker arm cover.

If the valve timing is off much, then you have probably bent the intake and/or exhaust valves when they hit the piston. (mine were) That will require removing the cylinder head to replace the valves.

Good luck.

 

CurtG, the 800 has a push rod valve system and doesn't have a chain and the cam is internal,but you've described quite nicely one of the things I came across on a 500 engine also! OPT

 

I have a persistent rattling sound in My 98 Sportsman 500. It sounds like a washer or other small part rattling in an enclosed area like radiator cover or something like this.
I have removed all plastic and other parts that will allow the machine to run. Still have the rattle. Any suggestions would be appreciated.
Thanks, Herb

 

A few areas I'd check as sound does travel,hard to pinpoint sometimes, is the recoil cover for any loose parts that may have vibrated out,rattling starter bendix or worn brass bushings in the recoil cover and engine case,plus not a bad idea to pull the valve cover,check for excessive cam chain slack,rocker arm clearances (.006),plus be sure to look at the exhaust cam lobe for wear as this model was in the year models that were affected.Plus even a fan motor bracket or loose/damaged fan blade hitting the radiator shroud could be the source of the rattle.Times like this is when a cheap mechanics stethoscope can come in handy also.