Hi i have a 2004.5 Polaris Sportsman 400 just wondering what the compression is. In the manual it says 50-90 PSI but that sounds too low. My compression test i got 50 PSI dry start and with a 1/2 ounce if oil i got 90 PSI. My quad still will not start i got good spark, gas and air i also rebuild the carb, i lapped the valves gaped them to .006, cant think what else to try unless i rebuild the top end thanks for any input.

 

Compression is between 50-90 psi on average because the exhaust valves are kept slightly open during cranking because of the decompression device on the cam. Before you go to far,might be best to do a leak down test on it to see if needs to be torn down or could be some other problem you're over looking. PLUS how ya lap the valves without taking it apart to begin with?? Sure you have the cam timed right,plus have you checked the bottom crank sprocket in case it sheared a woodruff key and threw timing off?

 

With the decompression valve on the cam you typically will not see actual psi of the engine. If she don't burn oil, or not much I would explore other options first. Is the old spark plug oil fouled or just a nice tan color on the porcelain?
My 99 500 I got something around 80 dry and 100 wet but it still had some life in it. Problem turned out to be in the carb and not engine.
I suspect old polaris tech will chime in soon.

 

Whoops should've scrolled down haha.

 

The woodruff key is in tacked I removed the top half to check the valves one intake was leaking so i lapped them all no more leaks and its timed right the spark plug was black another thing to add the spark plug is wet with gas

 

When i first bought the quad it would spit white smoke out of the carb when trying to start it

 

If it wont at least try to hit with a shot of ether,then I'd still do a leak down or double check fuel supply,etc. Plus simple things like a weak pulse(pick up) coil or too far from the flywheel can cause starting problems.Plus I hope you went by the manual on head torque as it takes several stages to do it right.

 

I tried starting fluid no go the spark plug is wet with gas its getting fuel, the pick up coil i moved closer can you test a pickup coil? I torqued the head bolts right criss cross pattern 22ft.lbs then 51ft.lbs

 

Torque bolts 22 foot pounds,then 51 foot pounds. Loosen bolts 180 degrees(1/2 turn) then loosen another 180 degrees. Then torque to 11 foot pounds. From this point torque 90 degrees (1/4 turn) then finally another 90 degrees (1/4turn) I think you left out a few important steps on this head. Plus if it wouldn't hit with starting fluid,something just aint kosher as they say. Pick up coil should show around 97 ohms resistance(+ or - 20 %) between the white and red/white wires.

 

OK thanks for the reply's tomorrow ill do some more testing and get back to you