Hi everyone,

I have been tearing my hair out trying to figure out what is wrong with my 1998 Polaris Sportsman 500. I found a forum from 2005 with two people talking back and fourth named Sgajan and Rungunner. My issue that I am praying to god that one of you know the answer to is; the atv was running great no problems at all then I got it stuck and like an idiot I was goosing it and running it wide open rocking it back and forth finally when I got it out I realize that is was bogging down and running like crap and loud... I figured that is was backfiring because the exhaust was leaking so I put new exhaust gaskets a new muffler but that did not fix it... I took the carb off and cleaned the crap out of it... put it back together and it is still running like crap... the other forum the guys tired everything and they finally thought it was the exhaust lobe, the cam. Rungunner said he just got his parts and would post to let everyone know if that would fix it but then never reposted... I cant really afford to just keep on guessing and dumping money into this atv and no progress... If I did not mention it is also backfiring through the carburetor, it has a new spark plug and the compression is somewhere around 95psi but the battery was also very low so I don't know if that has anything to do with the low compression. I took it to the local atv garage to see what they think but they are 50 bucks an hour... please help the url to the other forum is http://forums.atvconnection.com/pola...-give-gas.html

 

Back firing and bog is a common problem on per H.O 500s when the center exhausts cam wears. There is hundreds of post about it.
Sportsman cam pics.... - Polaris ATV Forum
and
Polaris Camshaft - The Garage Journal Board

 

right I just did not see any conformation and I have worked on vehicles for the last 8 years but I have never tore apart the atv... I am not to familiar with small engines... The guy I took it to said that if it is the exhaust lobe I am screwed... he said that no matter what anyone says no matter what you do once you break the torque on the top of the motor to get to the exhaust lobe you have to do new piston and rings and if you are going to that might as well do crankshaft bearings, and for him to do it I am looking at 1300 bucks... what do you think?? this guy has great reviews but seems a little shady

 

LOL.

You know haw many people changed the worn cam on the 425, and 500. Its almost a common procedure.
I know of people who even changed the cam, on pre 2001 that did not even have a cam problem.
They just changed the cam because they wanted the higher Duration H.O cam for more mid and top end rpm.

Google it, "Polaris Sportsman bad Cam" They all fixed it without a piston change.
here is a post from this site. http://forums.atvconnection.com/pola...-camshaft.html

New motor just over a worn Cam, is unheard of.

 

Okay thank you, One more question for you was the compression okay?? it was right around 90-95 but the battery was pretty much dead, and okay I will get it back from him and tear it apart best place to get the cam and the rocker arms is ebay?

 

I,m not even sure is a compression test is possible on the 500 Fuji since it has a automatic decompression system for easier starting.

My 350 is a lot harder to pull over then my 500 due to it.

 

500 Fuji? Now you have me confused I have a 1998 Polaris sportsman 500

 

Fuji Heavy Industries has made Polaris engines for years.
Polaris Announces Buyback of 3.96 Million Shares From Fuji Heavy Industries | Business Wire

Fuji Heavy Industries http://en.wikipedia.org/wiki/Fuji_Heavy_Industries has made Subaru cars for awhile.

 

oh okay... see I told you I am idiot when it comes to these small engine and anything that is not a vehical... some one had stolen this four wheeler back 3 years ago and when we covered back they had crashed it into a ditch between two fields and I took water out of everything and got it running again... but I had to do some jerry rigging with the electrical such as taggo switches instead of the key and I had to unplug and rewire that black box that if working correctly would not let the machine go "fast" in reverse, I didn't think to mention any of this, this does not change the opinion that it is still the cam shaft exhaust lobe thing correct? and okay prob get the bigger carb 40mm anything else I should replace, cam shaft rocker arms, carb, obviously new gaskets, any other advice for something to look for? when the odometer stopped working 5 years ago it had 15,254 miles on it.

 

PLEASE don't double post in the expert section and also the normal thread area on the same problem as it causes confusion for you and everyone else. Continue any added response either in this section or the other not both. http://forums.atvconnection.com/pola...ml#post3101423