Hey guys, I’m new to the forum, I’ve been looking thru and have seen lots of good and helpful advice. I’m hoping someone can point me in the right direction with the problem with I’m having with my 2003 Sportsman 500. My quad starts and runs good for about the first 5-10 minutes/4-5 miles and then it bogs down and has no power for about another 5-10 minutes, then it picks up and runs good for the rest of the ride. It started this after I adjusted my valves (coincidence or not?). When I leave from my home out of town on the same trail it will do this every time on pretty much the exact same spot on the trail. When it’s bogging down it feels like there is no fuel or week spark, if I give it gas it will backfire and sputter, so I just throttle down to where it will stay driving until it gets it’s power back.
Any advice would be greatly appreciated, thanks.

 

May or may not have anything to do with the problem,BUT wouldn't hurt to recheck valves, new plug,? If ok, I'd go to fuel system,check for water in fuel,fuel pump breaking down,(usually pretty reliable). Backfiring you say?? First 3 things I can think of that can cause backfiring is fuel,electrical,cam exhaust lobe wear/valves too tight????

 

Thanks old polaris tech, if I get time in the next week I will recheck my vavle settings. Does the cam have to come out to check for exhaust lobe wear, if there is wear will it be visible by eye or does it have to be measured? Thanks.

 

Just pull plug out(easier to pull recoil rope)) from recoil side look at lobe on intake at far side of head,THEN compare to center lobe as it goes around. Lobe should full, not ground down OR no lobe at all (as a lot I've found), if all ok then recheck valve clearance at TDC.

 

Hi, I just registered to this forum to try and help you, cause I know this problem is frustrating, it happen to me in 2007, on a ride my 03 sprortsman suddenly started to sputter and lose power, at idle was ok but as soon that I would give it gas - sputter and bogging down, backfire and all, let go of the gas and would idle fine, seemed like it was hitting the rev limiter in forward or neutral, brougth the bike home and took the carb all apart and cleaned it althougth it was not dirty, cleaned air box and filter, new spark plug, started the quad and problem was still there, took carburator apart again hoping I had missed something, reassembled and tested good and thougth I had fixed it, my atv ran good for two rides and problem came back, for the next year my quad would do this from time to time not knowing the reason until one day while it was doing it I decided to take my ligth pod apart and disconnect my speedo since it controls the rev limiter, and BINGO !! it revved up ok, plugged it back in and try to rev up and would sputter and no power, disconnected the speedo again and cleared the problem.
I've installed a new speedo and never had a problem since.
I purchased my speedo on Ebay at half the price, they wanted $400 at dealership here in Canada.
Hope this helps you, cause I was getting frustrated.

Good luck !!

 

Thank you Polaris Rider. Last night I got the quad back together, I re-adjusted the vavles - which seemed fine, took apart the carb and gave a complete cleaning, cleaned up most of the electrical connections - found and fixed a bare/wore wire which came from the radiator sensor, and put in another new spark plug. I will try it out hopefully tonight (wedding anniversary today so it might have to wait till tomorrow) and see what happens. If it starts to bog I'll unplug the speedo and see if that makes a difference.

 

Forgot to add, the lobes on the cam look the good.

 

If it is the Problem there is a way to by pass the rev limiter rather then buy a new speedo. Hope Polaris rider did not throw out his old speedo.

 

So I tried the quad out again today, same thing but worse, from the start as soon as I'd give it gas it would sputter and backfire, at low rpm it would work fine. I unplugged the speedo and no difference. When I turned it off the battery did not charge enough to start it, which is unusual as it normally starts good unless it's been sitting for a while. I put it in diognostic mode and pull started it, the voltage gauge would jump all the way to 16.1 volts when I increased rpm to 1500, is it normal for a battery to be charging that high? Thanks for the help.

 

16.1 is way to high, at 4000rpm it should be between 13v-14.6v my manual says.