I'm not sure but I think the timing may be fixed with little adjustability, or not adjustable. If you have spark it may not be stong enough. If you take the flywheel off you'll find the stator, thats whereyou will see if you can adjust the timing or not. You probly need to clean the stator real well with say contact cleaner, unscrew the screws that hold it down and make sure theres no corrosion on them or the mating surfaces. Clean the surfaces of the stator with sandpaper . Some preditor 90's have problems with stators going bad, if you ride through water I would suspect you might be having the same problem. Also you could have corroded contacts where two wires connect together.

 

Where is the stator - is it hard to get to? How will I know what it is when I see it?

 

Its on the right side , where the fan is. You need a flywheel puller to get to it, or a steering wheel puller.

 

Well, I give up. After 5 1/2 months of working on my son's ATV, it hasn't cranked once since the problem developed. My frustration level is pegged out. Nothing has worked. I cut off the muffler and got it to cough pretty good but it wouldn't crank at all.

Fortunately the local Polaris dealer finally agreed to look at it. It's in the shop now. I'll let you all know what they tell me.

Thanks to everyone for their constructive help and suggestions.

 

Hawkdriver, I'm sorry we could not figure this out for you. I know your frustration; been there a few times myself. Sometimes you just have to throw in the towel and let someone new take over.
Do us all a favor and let us know what they found out so we can all learn.

 

Bummer

 

I finally got my kids Sundiro back from the shop - it's a Polaris shop, so it is limited in what it could do. However, their diagnosis is that the piston on the top end is "scored" and is leaking fluid and compression. The mechanic was certain that a new set of piston and rings would fix the problem, and possibly a new "top end".

This is all a bit beyond me, but as I recall, piston and rings aren't very expensive. What about a new top end? Any one have ideas on where I can find one and how much it might cost? Thanks again...

 

In an earlier post you said you checked the compresion and got 120 lbs. My sons would still run when it was down to 70 lbs. If you in fact have 120, I would look elsewhere for the problem. How did they determine your cylinder was scored? Did they take it apart? If you do a top end you can bore your stock cylinder from 50mm to 52mm and use a wiseco piston and rings or a stock one from polaris. Good luck

 

I thought about the compression readings as well - the same mechanic told me a number of weeks ago that it should run with as little as 60-90psi compression (as you said as well). However, now he is saying that the 'scoring' on the piston is causing 'blowback' and it's blowing fuel/air back out of the carb instead of sucking it in. This is all a bit beyond me, since I've never gotten this far into any engine. However, he was pretty convinced that is the problem. They didn't charge me a dime to trouble shoot and didn't try to sell me any parts.

Still - I'm convinced the experience exists in this forum to diagnosis the problem for good. Is it possible to have good compression yet have blowback that would prevent the engine from starting?

 

I forgot to add that the mechanic took off the reed block and looked at the piston as it would cycle and saw this 'scoring'. He is assuming there is similiar scoring on the cylinder wall that he couldn't see.