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I bought a used 2004 sportsman 90 for my kid a couple years back , it ran fine for awhile and then it started acting up by starting hard, not wanting to idle, and then it would idle but would bog down on acceleration and die.. after doing the simple stuff like spark plug, air filter, carb cleaning, my neighbor who was a motorcycle mechanic in his younger days diagnosed a low compression situation on the motor. I ordered all the parts to go thru the motor and hired him to do it. The starting situation improved, but we couldn't get the carb adjusted make it run right from idle to acceleration. My neighbor researched these small ATV's and saw that the carburetors they sold said they were good for both the 50 and 90cc ATV's. In his experience he said that the jetting is going to be alot different when you almost double the size of the motor. I ordered both a pilot and main jet kit of of Ebay and my neighbor talked to some of his fellow motor heads and got some preliminary jet settings to start with. It took about 4 attempts, but we found the jet sizing that made the machine run beautifully, starting easily & accelerating smoothly with nice top end performance. For those of you who've beat their heads against the wall to make their sportsman 90 run right, try an initial pilot jet size of 32.5 and a main jet of 95 and set the pilot adjustment screw out 1 1/4 turns. Drive the machine a bit and get it warmed up and fine tune the pilot adjustment screw and idle speed adjustment on the carb slider.
 

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My neighbor researched these small ATV's and saw that the carburetors they sold said they were good for both the 50 and 90cc ATV's.
If you are buying a carb from Ebay or Amazon the ad copy is correct FITS 50, 70, 90 and 110cc ATV's - it is the responsibility of the buyer to assure jetting is correct for their application. You said you cleaned the carb - the jetting should have been correct for the application with the only exception being fuel alcohol content. The Chinese do not have alcohol in their fuel. Adding alcohol to gasoline raises octane and lowers BTU output of the fuel - thus, you have to rejet the carb to compensate for the decrease in fuel quality. Not the size of the engine.

Carburetors are jetted for the flow characteristic of the carburetor, not the size of the engine it is being used on. Note: if you buy a cheap Amazon or Ebay carb, you may not be able to get replacement parts and there is no guarantee that Mikuni or Keihin jets will fit correctly - many times the Chinese carb has a different sized thread on the jet than either Mikuni or Keihin.

Regardless; of the jets you quote you do not disclose what brand of jet or carb they were used in and just so you are better informed; some Mikuni jets are sized by orifice size and others are sized by the amount of fuel the jet will flow in a specified time period. So one style of Mikuni jet stamped 150 flows a completely different amount of fuel than another style of Mikuni jet stamped 150. At the same time, a Keihin jet stamped 150 may flow a different amount of fuel than either of the Mikuni jets with the same size marking.

Typically the cheap Chinese carbs come with jets that are not marked as the jets are sized for the flow characteristic of the carb. 20 of the same carbs may have 20 different sized jets as the air flow characteristics may be different for each carb manufactured.

There is no chart definitively specifying what size jet to use for what carb used on what engine. Each carb is jetted to perform acceptably by the end user. Now most engine and carb manufacturers have quality control that allows them to make thousands of units that perform acceptably without individual tinkering. The Chinese machines have little quality control. therefore most Chinese manufactured Polaris models use Mikuni carbs so the tinkering is reduced to a minimum, but line up 10 Polaris 90's and each one will perform differently due to manufacturing variations in cam profiles and ignition systems.
 
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