Hey guys, I've been searching the forums for over a week trying to figure out this quad. Its a 2004 Polaris Sportsman 500 HO that has a no start issue. Not sure what I'm missing so some help would be much appreciated. Heres what I know so far

Cranks strong
Has strong spark
Has 60psi dry compression at wot
Timing marks are lined up
Flywheel key is fine
Valves are adjusted
Cams look healthy
Coil ohmed good
Exhaust is unhooked to eliminate clogged exhaust issues
Tried 2 new spark plugs
Poured fresh gas directly into cylinder
Tried a little starting fluid as a last resort
Won't even try to fire ever!!!

Only thing that doesn't make sense to me is the plug is never wet when I pull it out after cranking.

 

Hello,
How much gas is nowin the oil? You should check that and change it if needed. Pooring gas directly into a cylinder is not a good idea, just my opinion.
So what happened to the machine. When was it last running and now it won`t. Give us the history please.
How did you check spark?
If it truly has correct spark and you spray starter fluid in the intake with the choke off it should fire.
Sounds like timing if all else is correct.

 

Please forgive me for butting in, but isn't the compression mighty low?

 

Thanks for the reply,
I only put a spoonful directly into the cylinder once as suggested by another post on here(one of the last things I've tryed because I'm running out of ideas). Engine oil is currently on the lower end of the dipstick and doesn't smell at all like gas. I was told it sat over winter and then wouldn't start in the spring so i did the usual fresh gas, clean carb, ect, ect. Spark was checked with an adjustable gap spark tester. It jumped over half an inch gap and has a nice blue snap. I checked cam gear and flywheel timing marks and they lined up. Do you know what triggers ignition timing on these?
Thanks again!

 

I thought that was the problem at first aswell, but with the automatic compression release I think 60 is within spec.

 

The compression release on the camshaft disables at very low RPM. If you can crank your engine at a decent speed, it should show much higher compression. 60psi compression is not enough to fire.

Since you checked valve clearances, I suspect worn rings.

 

Okay good to know, we might be on to something here. So using electric start with a strong battery wouldn't activate the compression release? When I get back out in the shop I'll do some more testing on it. 👍

 

In the engines I work on, the CR mech on the cams have very light spring and seem to deactivate when the cam it turning at anything more than very low speed. I can usually get meaningful comp test result with a good battery, cranking with throttle open. Good enough is anything over about 90psi.

Note that the first thing damaged by inadequate air filtration is the rings. You can often fix without boring the jug.

 

Well you figured out my mistake! Got back out in the shop tonight and did some testing. Dry compression test was 60 psi again. Added some oil and compression shot up to 110ish. The auto compression release obviously doesn't affect the readings like I was told. Guess I'll be tearing this engine apart, thanks for the help.

 

Two more cases in point:

I just did a compression test on a Can-Am Outlander 400 EFI. I can get 145 psi on the gauge when cranking with a charged battery and a battery charger connected. I did not even try the pull-starter. Engine runs fine and features a decompressor on the cam gear. You DO need to hold the thottle open with the electric start test, and EFI engines hate that.

A couple of days ago, I was working on a Honda GC190 engine, with OHC and decompressor. Pull-starting got no more than 30psi, as I could not crank it fast enough to get a good reading. Engine seemed to run fine, but bogs under load. No exhaust smoke.

Compression tests with pull-starter and decompressor on the cam are useless in my experience. Electric start compression tests can be useful.