I've got an 04.5 SP 500 that I put in a bigger jet, 155 to 162, for better cold weather running, and now when I accelerate on an uphill slope I get sputtering and backfiring. If I back off the throttle and don't open it up too much it will pull the hill but if I open it up to 1/2 to 3/4 throttle it's starts to sputter. Since this is the throttle range where the needle supplies most of the fuel, I'm wondering if it's a lean backfire situation and I'm thinking I need to raise the needle a notch to get a little more fuel. It could be a low float too but this didn't happen until I changed the jet. Any ideas?

 

sounds like your too rich maybe try a 158 or 160

 

I guess that's possible too, I might go back to the 155 and save the 162 for winter. But why would it sputter going just uphill, you would think that with the increased load on the engine that more fuel flowing would be a good thing.

 

the easiest way to tell is to pull out the plug and see what it looks like to see if its running too rich and im guessing it is. but your float may be out of wack as you supect since it only does it up a hill. if you hammer on it on the flat does it do it, if not then check f. level. most people dont change their jets unless your running in real cold weather alot.

 

I suspect your right and it is running rich so I put the 155 back in. This has only happened when I've been in the mountains and gaining elevation so that fits. I changed jets this past winter when I was plowing as it didn't want to idle without the choke out a little, the bigger jet fixed that. I may have to swap out back and forth which is no big deal after you've done it a few times. I did have some float issues in the past where it was set too high and when I would dip the nose of the machine down it would flood out and gas would run out the overflow tube so I've got it set as high as I can without that happening.

 

You are jetted way too rich that is why it's sputtering. I don't know why you would have to jet up for the winter as they came over jetted from the factory. I jetted my 500 down to a 147.5 and ran it that way for years summer and winter in temps down to -20c with out any problems. It will work much better in the warm weather and once warmed up ran fine in the cold........

 

actually, if you are running into a cold weather idle problem, increasing jet size should have no effect on this since the main jet only operates at or near WOT...I would think adjusting the idle screw would be the right way to go for the cold weather idle problem...I would have to agree that going back to the original main jet should solve the problem.

 

I've heard that you're supposed to re-jet below a certain temp. I don't remember if it's 32 degrees or 40 degrees or something else. I've also heard a lot of people say that Polaris' are jetted way too rich from the factory (so the motors don't burn up). I think they jet them to work for for the national average temp year-round. All I ever did on my old ones was crank up the idle in the winter like Jokout said, then I would turn it back in the summer. It ran okay, but not at peak performance, anytime of the year. Sometimes it was hard to start in winter, and sometimes I had to leave the choke halfway on for a long time, but it ran. In the summer I usually didn't need the choke at all.

 

Well the problem persists.......I jetted down to 150 and it's doing the same thing sputtering and popping on WOT going uphill. I check the fuel pump with a vaccum gauge and it holds 5 psi like the book says. I then checked the float level on the carb using the overflow tube as a float gauge like the book shows and it reads right on and maybe just a touch on the high side but not much. Anyway I'm stumped, it feels like it's starving for fuel as when it starts popping and sputtering I back off the throttle and settles down. I checked all my vent lines and fuel line for kinks and all is good there. Could it be that even though my fuel pump is holding vaccum it's still weak at WOT? Or maybe I need to raise my needle in the carb a notch going on the premise that I need more fuel. Any ideas?

 

MAKE SURE YOUR THUMB THROTTLE HAS 1/8" SLACK EVERYTIME I MESS WITH THE CARB IT CHANGES///