hi M Quick
I do have the service manual and yes I saw that where it says 65psi.. but that seems way to low.
there must be a decompressioner of some sort.
the bike seems to be having problems.
It can use 1/2l of oil for an 80k run
most times when starting cold it can be a real bitch. It will back fire in the air box and the exhaust.then It most times will start but today it wouldn't start.
the bike was used hard before we got it so god knows what was done wrong.
is there a way to check the fuel injection?
As far as the compression being low, Idk maybe one of the engine builders can chime in. The manual says 65lbs, so I'd say if its atleast that its ok. Now I see why it seams low, heres a paste from my 2004 Polaris Predator 50/90cc Sportsman 90cc manual. And note compression is higher in the 50cc unit?
Cylinder Compression: 0--1000 ft (0--300m)
50 cc models: 110--130 psi
when I did a compression test I was geting around 80 so it seems good like that.the bike doesn't smoke , i would think it would be with it using that much oil. We did a fresh oil and filter change I'm hoping this may help.
The backfiring into the intake/airbox would indicate that the intake valves were not closing all of the way, so the combustion was escaping in that direction. I would check the tappet clearance - if the clearance is too small, the intake valve(s) could be hanging open slightly, which could be causing the lower value on your compression check. Make sure you are at Top Dead Center when adjusting.
As far as the oil consumption, it could be leaking out of one of the drain bolts, so check the sealing surface for anything wierd like debris, and try changing crush washers. If its not leaking out of a drain bolt, then it must be burning - meaning that the oil is coming past the piston rings or valve stem seals.