when I run at the upper end of the throttle it misses like is is starving. I discovered that if I remove the airbox lid it runs much better. It has a K&N air filter and I'm guessing must be jetted (bought used so i'm not sure) or I wouldn't be seeing this symptom. I'm guessing that modding the air box would be the easiest way to solve my issue?

 

o maby it should be rejetted I have a 2003 500 2/4 with a sportsman 500 engine in it but it also has a k and n air filter in it bought used and does not have a jet kit and it has a lil lag at the bottom i ask the prev owner and he said it has stock jets so i whant to rejet. but i don't know what i can do that is easy and i don't have to constantly rejet whenever temp changes or to dial it in.

 

You shouldnt have to rejet with just a K&N filter.Try cleaning the filter and reoiling

 

I did clean and re-oil filter, mine has a custom exhaust as well.

 

Then pull the carb and inspect the diaphram and clean the jets.You need the airbox lid on for the CV carb to get the right amount of vacum to opperate right

 

Thanks ftw, i'll do both tomorrow after work. This is my first quad so I'm trying to educate myself. I going back through old posts and reading different articles it seems my problem is that it is running too rich on the main jet. Will a bad diaphram or dirty jets cause it to run rich on the main jet?

 

Diaphram can cause alot of it.

 

Diaphram looks good. Jets have been cleaned. It did appear that the spark plug wire was not seated properly. I replaced the plug and will try to get it all back together tomorrow and report the results. It has a 160 main jet.

 

Try raising the needle one notch, this will give it more gas, Move the e-clip down.

 

Ok, it is running better but still runs kind of sounds like it's missing in the upper throttle ranges. Removing the airbox lid no longer fixes the problem. Compression is normal, I'm thinking I'll check the cam and adjust the valves next.