low compression in 1999 polaris xc 500

[tori's dad]

I have a 99 xc 500 polaris - it bogs down and backfires - has plenty of midrange power but bogs down heavy with full throttle and then backfires through exhaust when coming to a stop and idle. carbs were cleaned twice and plugs changed out- only owned the sled for 2 weeks. compression is 96 on one side and 106 on the other. My mechanic friend thinks i need to freshen up the top end with new rings. Anybody else have any ideas to check- oh clutch is good too. Thanks

[leech~~]

I have a 99 xc 500 polaris - it bogs down and backfires - has plenty of midrange power but bogs down heavy with full throttle and then backfires through exhaust when coming to a stop and idle. carbs were cleaned twice and plugs changed out- only owned the sled for 2 weeks. compression is 96 on one side and 106 on the other. My mechanic friend thinks i need to freshen up the top end with new rings. Anybody else have any ideas to check- oh clutch is good too. Thanks

Do you know if one of the heads were rebuilt already? Look at the head bolts for any rounding or something that may tell you it had been worked on already. If it has then your buddy maybe right and you need to get them both done so they run evenly. But it may just be that your carbs are out of sinc and just need to be adjusted the same. To me it sounds just like your air screws aren't set right? I think we need Macgyver55 to chime in here he is pretty knowledgeable about sleds!

[Tyler23]

idk what i book says but from what ive learned that compresson numbers seem low. my old 600 rev had 135psi and my indy 500 had 120 they both ran great. and that seems like alot of fluctuation between the two cylinders. im thinking its time for a freshen up

[Macgyver55]

Normal compression on that sled is 125 psi. 100 psi is kind of the minimum threshhold where a 2-stroke will run well. If the readings you took are accurate, then it is too low and a top end "freshen up" would make a big difference in performance. Also, the fact that there is a 10% difference in compression between the two tells me there is a need. But, its always a good idea to double check with another gauge to verify that its correct. Also, when you check it leave the ignition off, and have the throttle open when pulling. If the readings you took are accurate, it needs to be done.

[tori's dad]

Thanks for the information, I will check those items that were pointed out first before tearing into the motor. This site is wonderful that people share their knowledge with one another.