[PolarisRich]

2005 Polaris Sportsman 500 HO Carb

So yesterday I had a problem with my 500 that is starting to baffle me a bit. I do have some ideas but I want to see what you guys think. Here's it go!

I was out on my bike screwing around and it runs great. Lots of power, idles fine and runs the same as it always has. The only thing I noticed was after a short wot run and as soon as I let go the throttle it backfires. I didn't think to muck of it at the time.
Now I decide to make a run down the ice when all the problems start.
I hold the bike at wot for about 30 seconds and all is fine then all of a sudden it starts backfiring and dies. It starts back up with no problems. I take the bike home and change all the fuel over to fresh premium gas and it did make a difference. I then cleaned the Uni filter with no difference still backfiring and dieing at WOT. I changed the sparkplug and fuel filter with no change. I then pull off the fuel pump and cleaned it. It was full of mud on the vented side.
Cleaning the fuel pump did make a slight difference. The bike now does NOT backfire at WOT but it now sputters and dies at WOT after about 30 seconds.

 

[PolarisRich]

Spark plug looked perfect! I cleaned the battery posts and checked all the electrical connections. Next I pull the carb tonight.

 

[fuzzyfireman]

Is there a chance there is ice in the vent line for the fuel tank?

 

[PolarisRich]

I thought that too! I pulled the tube out and blew threw it. No obstructions. I even opened the gas cap and it did the same thing.

 

[fuzzyfireman]

when you pulled the plug, what color was the tip?

 

[PolarisRich]

The plug was a light tan. It looked the fine.

 

[fuzzyfireman]

It almost sounds like the floats are sticking partly shut, only allowing the needle to let a small amount of fuel thru, causing it to run the carb dry WOT.

 

[PolarisRich]

That's exactly what I'm thinking. I'm wondering if it is a known problem with bike.

 

[fuzzyfireman]

Personally, I haven't had any carb issues. The only thing I had happen is the throttle cable wore/stretched and caused the contacts in the throttle ass'y to go out of alignment. It too would backfire and stall when the throttle was released, but it did it at most speeds, and it would not idle either.

 

[PolarisRich]

I did pop the top off the throttle box and everything look fine. There was at least a 1/8" gap between the two contact points.

 

[Offroaderzav]

I bet your carb boot is leaking. Spray some wd-40 or some flammable spry around the
cylinder where the rubber carb boot seals to it. Spray the whole boot it can be cracked as well.

 

[PolarisRich]

So last night I started the bike and let it idle and sprayed the carb boot 3-4 times soaking the hell out of it and nothing! Ihe idle never changed even 1 rpm. I used carb cleaner. I would think that's flammable.
How do I check the fuel pump? I did pull off the line off the carb and started the bike and the fuel squirted out only about 1/2 to 1" from the hose. Is that enough?

 

[Kenskip1]

a Backfire is the cause of a lean mixture.I would make a guess and say that you have water in the carburetor.Water being heavier than gas will not be drawn into the cylinder.Centrifugal force is allowing the water into the main jet causing your problem at WOT.Does the bike have a carburetor drain on the bottom of the bowl?This is were water will accumulate being heavier than gas. Hope this bit of knowledge will assist you, Ken

 

[Offroaderzav]

I was hoping it was the carb boot, its a easy fix! I fixed a 04 500 that once it was warm it would start to backfire & would keep getting worse as it ran till it would stall. Once cool it would fire up & do the same thing over again. I replaced the stator & the cdi now it runs like a champ. Hope that helps if you cant find the problem.

 

[PolarisRich]

Kind of a pet peeve of mine are threads that people start about a problem there having with there bike and never posting a solution or resolution to the problem. So with that being said!!! Here we go.....


"UPDATE"/"SOLVED"

So yesterday I decided to get off my ass and tear into this problem. I 99% sure I got this problem solved. I pulled the carb and the carb boot off. The boot was clean with no visible cracks or dryness, looked like new! So now to the carb. I drained the fuel from the bowl and it clean clear with no water. I pull the bowl, floats and jets, everything looks perfectly clean. The needle, diaphragm and slide are clean with no damage.
I start to reassemble to look at the float height and it looks good nice and level. So I decide to put a hose on the fuel inlet tube and blow threw it while rotating the carb. BINGO! With the floats in there lowest position I had almost no air flowing past the needle and seat. I readjusted the float tang and repeated the process of tipping the carb and blowing into the fuel line and to my surprise I almost doubled the amount of air I could get past the seat while getting the float to sit level with the first touch of the needle to the seat.
I believe the problem was with the needle itself. It is an aftermarket needle and the spring tip is at least 1 mm longer than the stock one, plus the wire that hangs the needle to the float was also longer than stock.
I put the carb back on the bike and decided to adjust the engine valves before starting. Both exhaust valves were tight to the point where I couldn't get a .003 feeler gauge between the valve and rocker. The one intake was way loose (.012)and the other was perfect. After a few adjustments all the valves are now at .006mm.
I put everything back together and to my surprise the bike started after only a second or two of cranking without the choke. Huh!
The bike is idling smother with less valve train knocking and taping. I took it for a quick rip down the river and the bike ran great. Running Strong with no backfiring when I let off the throttle from WOT and it didn't start to die when I held it to the bar for 30 seconds.
So I believe I have my problem solved, but I only say 99% because I need to get out on the lake so I can hold it longer at WOT (60sec). If the bike doesn't die within 60sec then I'll be 100%.

 

[PolarisRich]

Spent the day today out on the ice and I can now say it's 100% fixed. Not one backfire and it never skipped a beat!

 

[al53]

Thats good news Rich....I like how you explained the fix..it can help others or my self in the future...But as you said..some come here with a problem..a few days later they say fixed with no explanation of how....good job

 

[eisej]

Great post btw Polaris Rich. Really helpful. I just did a complete rebuild of my 2000 Sportsman 500 and I was having problems with the idle hunting and after a high rev I'd get a stiff backfire. With a medium rev she would fart a little. I made a quarter turn out on my pilot screw and it ran like it was new after adjusting my idle screw a quarter turn. This was after it being set to factory of 2 5/8 turns out. I also set my mixture one slot up from the bottom. I'm not sure what the default is. It was originally set to the very bottom. Just thought I'd throw my fix in since it has the same symptoms.

 

[james53ericcx]

I installed a dyno jet kit, cleaned the carb good when i did. Jet kit gave the bike a little more pep.