Hi I am new to this site, but for the last 5 months my 98 trailblazer es doens't start anymore after the last time it ran. when it was running I was hearing a strong whistling sound for about 30 seconds, then it went away. when i got it home is shut off on it own, and now wont start with either the electric start, nor the pull start. I've changed the spark plug thinking it was fouled out, but that didn't work. I've checked for spark, which there is. It just keeps rolling over until it almost starts but never actually does. I am so confused on what's wrong. I am thinking maybe a scorched piston or something along the lines of that. please give me some input if you know or have any suspicion on what it could be. Thank you very much for taking the time to read my post.

 

First things to always check on a 2 stroke is fire (good you say) and compression. If compression is around 115 or less,then time to check into the top end. As I've mentioned dozens of times before,if it is a piston problem,I would not just do a top end on an old machine without doing the bottom end as well!! New rod kit,crank bearings and seals,BUT this would be your call on this one!

 

just went through what sounds like the same problem with a 250. rebuilt top end without crank seals and ended up putting in crank seals under advisement of old Polaris tech and away it went.

 

How does replacing crank seals affect ignition? I can understand how it could increase wear and cause premature failure by letting in junk, but how would it affect starting/running? I do not understand ...

 

Crank seals don't have anything to do with ignition. You have to have good top end compression and also bottom end compression for a 2 stroke to run properly along with with spark,fuel and air. You can have decent top end compression,but if either crank seal is leaking, the gas/oil mixture can't compress(atomize) in the bottom of the crank case and isn't able to go through the transfer ports to the top of the piston for ignition.

 

When I said ignition, I did not mean the ignition system. I meant compression. I did not realize the crankcase was part of the induction system. I did not realize there was such a thing as a piston port. That makes MUCH more sense. Who would have thought a Polaris 250 had such a system. With the carb dumping the fuel right into the compression chamber, I never considered the crankcase to have any purpose in the air/fuel mixture process.

THANKS! Mine is not running right, and I know the seal on the left side is not in mint condition. I will figure out where to buy new seals.

 

You need crank seals # 26 and 17. You can get em on Ebay, Cycle Parts Warehouse,etc,but shipping costs may cost as much as just going to a local dealer.Dirt Cheap Yamaha, Honda, Arctic Cat & Polaris OEM Parts & Accessories – Cycle Parts Warehouse

 

Off subject slightly, but if I am going to the dealer then: if the top end is bored larger (1 size jug bigger -- forgot the size though), would you suggest changing the carb jet? If so, what size?

 

No,jetting changes shouldn't be necessary on first over bores. 25 mm(.010) or even larger in most cases.

 

On a Polaris Trailblazer 250 am I able to see the crank seals without taking the whole thing apart? I am not completely sure they are bad but it seems like the only option. The quad isles crazy high unless the choke is on, we exhausted carb issues, throttle issues, so we are assuming it has to be an air leak and we checked everywhere else. Before I buy the clutch puller and start taking it apart I was curious if there is a way to tell which one is bad.