I have an 03 Sportsman 90. It will start but after you give it more than 1/4 throttle, it bogs down and dies, unless you release the throttle. I bought it used and it appears that several things have been done to it (now runs premix, air box removed and after market air filter put on). I have removed the electronic carburetor and put a manual carb/choke on it, replaced the CDI box. Still does the same thing. Also have an 00 Scrambler and had the same problem but after choking down the air intake on the aftermarket air filter, it fixed the problem. I am at my wits end. Hoping that OPT will have some ideas for me.....

 

Start at the beginning on your 03. Always check compression first to see where you stand. After that it's just eliminating one thing at a time. As far as your other 2000 model,I've seen this happen on after market open filters on the youth models. They run too lean for the most part.Either the carb needs to be rejetted to compensate for increased air flow or just put the oem box and filter back on and see how it does. Could be the same for the 03.Plus I wouldn't premix more than 40-1 ratio.

 

OPT, thx so much. After checking the compression , it was good. Next went to the spark plug , it was extremely loose so I tightened it. Still had the same problem so went to the air tube on the gas tank found that whoever had it before me put a screw in the tube so I removed that. Next checked the rev limiter and it seemed to be working fine. Next checked to make sure fuel was passing from the tank to the carb and it was fine. My next thought was that since a previous owner converted to premix the air to fuel ratio was off. Before I bought new jets I wrapped some electrical tape around the aftermarket K&N air filter and low and behold the problem is fixed. So I guess I will be buying a smaller jets so I don't have to keep a roll of electrical tape on hand. Thx so much for your help.

 

If you have to choke down the air filter to get it to run properly,you're shutting down the air to compensate for lean jetting and allowing more fuel to air ratio. If you keep this filter set up you need to increase the main jet size not decrease it.

 

So do I need to only replace the main jet or all of them?

 

Main jet probably only needed if its idles ok. First you can raise the slide needle a couple notches by lowering the e clip and see if it helps. If not I'd get a couple main jets. One size over stock,second main jet next size up from it. Can't remember for sure,but think the stock main jet is an 80.. Free flowing air filters do make a difference compared to the more restrictive stock air box and filter on jetting.