Hi,

I have a 2007 Sportsman 90 that after running for a while it won't run unless the choke is on and even then it runs rough. BUT if I open the fuel cap all the way, it will run fine for another 20-30 min with the choke off. What could possibly be causing this issue? Maybe a pinched vent line?

 

First thing I'd do is a compression check to eliminate that as a problem area. Must be around 115-155 psi or so for these little ones to run right as the manual says.If that's ok,check that the tank vent line is open,not kinked or blocked.Check valve clearance also. .002 clearance intake and exhaust. Easy for these to tighten up over time and when warm and can cause problems. Check that you gave good fuel flow from the fuel valve.If all the above is ok,then I'd head into the carb. Carb kits aren't cheap for these little 4 strokes,cheap knock off Chinese carbs are out there,but the oem carb is a lot better.https://www.ebay.com/itm/Shindy-Carb...VaD3jb&vxp=mtr If you need a manual here's a cheap one.2007 Polaris Sportsman 90 Service Manual PDF Download It can go into trouble shooting checks and tests to help also.

 

Thanks for the info! I just had the valves adjusted and carb was cleaned and jets drilled out by local dealer. I will check the vent lines and fuel filter/valve. I also had dealer check compression and they said everything was good. I explained this issue to them when I had it in there and they said the jets needed opened up, so that's what they did after checking everything else.

Thanks!

 

Not a fan of drilling out jets as unless they have jet drills to know the exact size or you can screw things up. If the stock jets are too small or needed change because of temp or altitude,simpler to change them out. We had a couple boxes full of Mikuni and Keihin main and pilot jets at the shop that we had for this reason.POLARIS Sportsman 90 main pilot slow jets kit