I just bought a 01 Polaris Sportsman 90 for $20 and it needed a carb since it didn't have one and also turned out the cdi was bad. I bought a carb for $20 aftermarket and a cheap $8 cdi and now it runs but after 1/4 throttle it acts like its out of gas so i put a pod filter on it (since i didn't have original air box) and to get it to run i had to tape over 3/4 of the pod filter. I'm thinking it might need a bigger main jet. What do y'all think? could it be the pod filter giving it to much air? do i need the original air box or is it the main jet? After the tape over the pod filter it runs at full throttle now and seems to run ok but i still think it could have a little more.

 

Taping over the filter just means it's running lean. Just get a new oem air box and filter for 24 bucks.NEW Air Filter + Box Polaris 0451080 50cc 90cc Scrambler Sportsman Predator ATV | eBay

 

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Chief, I just had the same issue with a Manco 90 (same chassis and engine as yours) that was driving me crazy. I fix a lot of Chinese atv's that are four stroke but no two strokes. So I had to get a new airbox and bingo she would take the gas. Now it won't idle, presumably because I had adjusted it to idle without the airbox

 

Can I ask how early in the throttle your clutch engages? MIne seems to take a lot of throttle to start moving.

 

Mine starts moving around a little less than 1/4 throttle. You may need a new belt.

 

Very well could be. The kids rode it hard for four hours this afternoon almost non stop! Still won't idle. I raised the slide needle, and played with the adjustments several times. I have the idle screw all the way in and the idle mixture about one and a half out. This thing is pretty fast on top end, even with my 200 plus pounds on it.

 

the air mixture screw controls idle and starting and the needle controls 1/4 to 3/4 and from 3/4 to max is the main jet. turn the air mix screw all the way in the out 2 1/2 turns then see if it will idle if so turn it in or out till it idles the fastest. if still no idle then try cleaning carb or check to see if pilot jet is stopped it or to small.

 

Ok, that is helping put things together in my mind. So it runs great at full throttle, but it bogs for a few seconds at part throttle (needle jet) and won't idle at all. I moved the needle down (rich) trying to improve idle, so that explains the bog at part throttle because it wasn't doing it before the needle change. It wouldn't idle but would take right off from part throttle. So I had the quad idling before I got a factory air box. But now with air box, no idle at all. With idle mixture all the way out and idle speed all the way in! So it seems too rich in the idle circuit if I am understanding this? In fact there is no change at all in engine speed until I press the throttle fully half way and the slide is half 1/3 way up. If I hold the throttle at the mid point (needle jet) it will run smooth as long as I hold that.