my kids runs a 2000 polaris 500 that back fires through carb and wont run above idle , at 1/4 to full throttle it bogs and dies. replaced plug, removed air filter, fresh fuel. read this entire post and this morning removed plastic, tank and rocker cover found exhaust lobe on cam worn almost round .....removed cam and will try with new..

 

plz! let us know how cams replacement goes, need to know asap, and how can i check the exhaust lobe on cams , where do i look?

 

one thing i noticed was with air filter removed and idleing as i gave it full throttle there would be fuel mist coming out of carb in to air box just before it bogged out. now to check the cam remove front plastic.( yes you can get it past the headlight pod with force) remove fuel tank, remove cover on top of engine 8mm bolts and start it up (wont run for long as only fuel in float bowl on carb) with engine running you should notice the intake rockers(out side two) moving approx 5/16'' and center rocker(exhaust) just barely moves, if this is the case your exhaust lobe is worn off. to be sure remove rocker shaft pedestals and rocker shaft(4 10 mm bolts) now that cam is expsed feel all 3 lobes all should be the same if center one is smaller and miss shapen cam is junk...to remove cam start by remove cam gear cover rh side, 8mm socket. down by pull start there is a 5/8 bolt sticking up remove this to see timing mark pull eng over to tdc. remove cam tentioner ( 2 8mm bolts rh side) . remove 3 bolts that hold cam gear to cam(mark gear to chain) tie gear up with wire keeping tention on chain. go to left side remove water line elbow fron head(2 8mm bolts, remove 3 8mm bolts that hold decompession cover on. and slide cam out left side carefull not to let decompression parts fall out of center of cam. when ordering parts get a manual $60 canadian. good luck

 

After reading 10 pages I still don't see where the initial problem was solved. My 04.5 SP 500 just started to exhibited the bogging and popping once it was given throttle. I went through all the steps except I didn't mess with the cam as since my problem happened suddenly and wasn't gradual I figured it couldn't be a worn cam plus I only have 1400 miles or so. Has anyboy out there pinpointed how to fix this problem? It seems like there's a common enough theme that it must be something specific.

 

Well I hate to break your heart but your probably not going to find the solution here unless your problem is the cam being worn down. I had this problem with my polaris and I spent a year and a half trying to fix this thing and I finally was able to get it working enough to sell it. My fix involved removing the air filter and that metal plate that retains the air filter, with those pieces removed the bike would run good as new. I have no idea why this fixed my problem but it did, temporarily atleast. I had many qualified techs scratching there heads on this one, no one could figure it out. I also have read just about every post dealing with this issue and the only sure fix is a replacement cam, if your cam is worn down, if not then good luck figuring this one out..

 

Yes, it is a frustrating issue, I took the fuel pump apart last night and found all kinds of sediment in the chamber and wondered where that could come from. I went and ordered a new pump just to see if that might be the problem. I know in my case that since it runs better with the airbox lid off it's either one of two things, getting too much fuel or not enough air. I'll keep trying and reading.

 

Fuel pump could be your issue. I went over my Fuel pump when I was having the same problems and mine was clean. Does yours run at full power with air box removed? or without air filter and retaining plate? Have you checked your valve clearance?

 

I'm hoping that the fuel pump is the problem, I had to order one from the dealer and it won't be in until next week. I did notice one thing when I took the lines off the pump was that there was gas present in the impulse line which the manual says is the result of a ruptured diaphram although when tested with a mitivac it holds pressure. However if there is gas in this line that would be dumping more fuel in the carb, I'm keeping my fingers crossed that this is it, if not I'm contemplated taking it to the dealer. Yes, I did check the valve clearance and it was ok. Mine starts fine and idles but when you open the throttle it starts to load up, with or without the airbox lid, the only way to keep it running it to keep feathering the throttle. As to why the pump is full of dirt on that one side is there are vent holes for each of those chambers to allow the diaphrams to get air, seems like a poor design especially where the pump is located in the wheel well where it is exposed to dirt, mud, and water.

 

I finally have up and took it to the dealer and he even had trouble fixing it. He went through all the steps I did, fuel, spark, etc. and couldn't find the problem. Second time around he found the problem, it was a small ring under the main jet that had deteriorated over time causing an excessive amount of fuel to enter the main jet system. The machine runs great now. The dealer had about 6 1/2 hours of time into it and only charged me 3 hours, which made me happy. The part number is 3130919 if you want to look it up. Never even saw this part when I had the carb apart.

 

I have the same problem ,bogs at half throttle. I replaced with new cam ,thats when the problem started. It works prefect with airbox removed,I replaced the airbox blocked onequarter of the opening, replaced the air filter,works good now.don't under stand why it just does.