hi
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 polaris sportsman 500 Motor boggs bad when i give it gas

 

You can still show decent compression even with a bad exhaust cam lobe. Because of the detent system that holds the exhaust valves open anyway while the engine is turning over,the compression reading should be between 60-90 psi on average,some a little higher. "IF" you haven't really looked or measured the exhaust cam lobe,this is what I'd check first. Usually they would idle good,but run crappy,back fire when you gave them any throttle.Your model is right in the middle of the problem cam area on the Sportsman/Scrambler 500 models.ONE other thing you can check is to pull the black wire from the reverse limiter module located under the front panel. If shorted out it can cause problems also even in forward range. Item #32 on the diagram. Dirt Cheap Yamaha, Honda, Arctic Cat & Polaris OEM Parts & Accessories – Cycle Parts Warehouse
Plus here is one members pics on a bad cam you can compare yours to. http://forums.atvconnection.com/pola...d-cam-pic.html

 

Thank you, yes that is what I am finding other people saying, what I forgot to mention is that three years ago or so someone stole this wheeler and when we found it it was submerged in water. water was everywhere but I cleaned everything out and changed the oil and still it would not run, I called a Polaris dealership and they told me to unplug something there under the cover in the electrical area, a black box but what ever I did it worked but I can go just as fast backwards as I could go forward I also have it wired so I do not use a key just push the red switch over and flip a taggo switch and it will start... now that I have shared that do you still think it might be the exhaust lobe? it has ran great since I did that I dropped it off an atv place and the guy said he has never seen it being the exhaust lobe and he could figure it out in a hour and even knowing he has a great reputation he came across arrogant so that makes me nervous, everyone on here is saying exhaust lobe.... thank you sir

 

Water doesn't help matters one bit also. By your description sounds like you did pull the correct black wire from the reverse limiter module if you now have full throttle in reverse WITHOUT having to push the over ride button,but if it still back fires I'd check the exhaust cam lobe. If the cam is damaged always replace the exhaust rocker arm also.RARE,but can happen is the cam detent return spring on the end of the cam either breaking or becomes disconnected from the detent lever.This can cause loss of power by holding the exhaust valves open a tad.Item #17.Dirt Cheap Yamaha, Honda, Arctic Cat & Polaris OEM Parts & Accessories – Cycle Parts Warehouse
One last thing you can try is to pull the black kill wire from the CDI module and see if the backfiring problem is solved. You wont be able to kill it though unless you choke the engine down or reconnect the wire.Not a common problem,but a cdi module kill wire can short out either allowing a NO spark condition or can mimic a bad cam or a reverse limiter module problem by not allowing full power. I've had to replace cdis for this reason.My best guess is still the cam just for the reason I had to replace so many of them on 96 to 2000 model Sportsmans.

 

This cdi that you are talking about is how I allow the machine to start and how I shut it off. I have it wired to a taggo switch and back to the terminal where it was. I believe I won't have it until Monday to look for sure.

 

Just checked the other forum and I saw your post, my apologizes I posted in there first then I saw where I could ask you, not trying to cause any problems just trying to look for answers, sorry again... So I should only ask you or in the other forum as I understand it? If you don't mind still helping me out I would like to ask another question that was on the other forum... I saw where people where saying to put the H.O cam on the wheeler and to upgrade the carb from the original 32mm carb to the 40mm carb... Is it worth it? is it mandatory?
thanks OPT

 

Just extra cost to convert to an HO. If the cam is the problem you can either replace it with an improved,updated one for your machine.#3086212. Item # 14.Dirt Cheap Yamaha, Honda, Arctic Cat & Polaris OEM Parts & Accessories – Cycle Parts Warehouse
OR you can replace it with a later model(2001 and up) model HO cam. 3085855 Item #14.Dirt Cheap Yamaha, Honda, Arctic Cat & Polaris OEM Parts & Accessories – Cycle Parts Warehouse You can use either one!
The ONLY difference between the two cams is lift duration.Lobe height is the same on both. It won't hurt to use either one as the cost is basically the same on each. To make it a TRUE HO you'd need a larger intake manifold and find a used BST40 mm carb possibly on Ebay as a new oem carb is close to $400. The choice is yours. Do you just want to get it running again at the least possible cost or don't mind the extra cost to convert it to an HO.

 

to put this all behind me If I have to spend a little more to get more out of it I will spend the money, I was up late last night looking up the information on the Polaris website under the parts catalog, I posted another forum stickly on the camshaft and the carb so I don't know if I can bring it up in here or if that would be double posting... I don't want to get in trouble for that and get kicked off again... can I delete a forum?

 

If you post something and later want to remove it while you're still logged in (over night is too late) just hit edit and delete the post. New people do this all the time on double posting. Just post in one area of the forum or the other to keep confusion down.Plus here's a pdf service manual you can down load to help you understand this engine.http://gh-ftp.com/ORV%20Manuals/Pola...0All%20Models/

 

okay cool thank you sir... I think between your help and everything I have read I am going to beable to tear this thing apart and figure it out,
thank you again