Motorcycle Repair: 97 Polaris atv 4X4 two stroke, polaris atv, stroke cycle

Question
QUESTION: have a 97 polaris 400 Xplorer I purchased, the guy said it was running a couple days befor I bought it he ran it up and down the street, then it would not start for him, he got fed up and sold it to me.

it will barely fire at times, andseems like the timing is off.
I replaced plug twice seems to spark well good fire.
took carb off and blew it out good twice.
took reeds out and inspected them look fine.
took exaust off no plugs
checked piston for broken skirt, looks fine.
has 80 lbs compression
fuel is getting into cylinder and if you hold hand over the intake with carb off sucks good.
tried either did not fire on it either.
could the timing be off? or am I missing something here.
the guy I got it from was a nice retired guy and had had it for a while. so dont believe he had it apart.

thanks for the help

Garry



ANSWER: The problem is the compression. 80psi of compression is not enough for a engine to run correctly. This is why is barely wants to start. You will probably have to replace the piston and rings on the machine to get it back up to par. Compression should be around 125psi or better after it is rebuilt.

---------- FOLLOW-UP ----------

QUESTION: thanks, when I say barely I mean just barely as in backfires. never actually runs. I know its low but wouldnt it at least fire on starting fluid, a little? or at least try to run. I have had some wore out stuff and they still started.  Is the there an adjustment on the timing at all?
and is there a way to check the timing on these?
I appreciate the answer just want to cover the bases before I tear the motor out.


Answer
No problem. I understand what you mean but there is no timing to check on a 2 stroke engine. The piston and the ports in the sides of the cylinder are the timing. When the piston goes up and down it covers up and uncovers the ports. This is the timing and there is no adjustment.

Like this:
http://en.wikipedia.org/wiki/Two-stroke_cycle

The other thing that is a big problem is that you are using starting fluid. When you use starting fluid on a 2 stroke you destroy the engine. A 2 stroke is lubed by the oil in the gas. Starting fluid does not have this and it is like running the engine with no oil. you are going to have to start with getting the compression back up and going from there.