I have a 97 Polaris sportsman 500. Has fire, fuel. Timing is right. I have replaced the stator, cdi box, plug. checked compression, from what I have read you cant do an accurate test due to the auto decompression. when I tested it if got 50 psi. need help please

 

Valve clearance?

 

Compression is normally between 55-90 Psi. Compression can show fairly good even if a cam has a worn exhaust lobe.That's the first thing I'd rule out along with checking valve clearance of .006 intake and exhaust. Common problem on the 500 cams until the HO models came out. Here's an example from a Scrambler 500. Bad Cam Pic - ATVConnection.com ATV Enthusiast Community Another thing you can try is pulling the black wire from the reverse limiter. Even though you may have spark,if the module faults it can retard spark in forward range also. Just pull the black wire from item #32 and see if it helps.

 

valve clearance is right and Cam lobes look good

 

I checked timing with a timing light and it is 10degrees advanced. Is that right?

 

"NOTE: The ignition timing marks are stamped on the outside of the flywheel. Ignition timing must be inspected
with the engine at room temperature (68°F / 20° C).
2. With the transmission in neutral, start the engine and set engine speed to 3000 +/- 200 RPM (3500 ± 200 RPM
for EH42PL, EH50PL).
3. Direct the timing light at the ignition timing check hole and check the ignition timing. NOTE: Do not allow the
engine to warm up. The timing will retard approximately 2° when the engine is warm.
If the ignition timing is not within the specified range, adjust the stator plate position as described below."


Timing mark is the center mark(30 degrees) If it's off remove the flywheel and either turn the stator plate counter clockwise to advance,clockwise to retard timing.Again pull the black wire from the reverse limiter and see if that helps. Plus rather than guessing,here's a link to a free pdf manual. https://www.google.com/url?sa=t&rct=...Z7Rqhg&cad=rja

 

I have unplugged the wire and still no change. on occasion it will backfire through the exhaust

 

Then go through the stator resistance checks and other electrical trouble shooting checks in the free manual I listed. This can help narrow down where the problem can be. Also pull the black wire from the cdi. This kill circuit wire could be a problem if it's shorting out in the cdi itself or in the ignition switch or left control switch.Plus wouldn't hurt to do a leak down test to see where you stand on the valves and piston and rings as far as leakage.

 

have you tried starting fluid? If it runs on that it'll point us in a better direction...

 

Leak down 80% not good