What is Wrong with My ATV Carburetor?

What is wrong with my ATV carburetor? This is what one Polaris Sportsman owner wants to know after his machine was left sitting his shop for seven years.

Here is exactly what the reader asked the ATV AnswerMan, followed by his response:

I have a 1997 sportsman 500 that I purchased new.  I left it sitting in my shop for about 7 years.  I started it occasionally however when I took it out on the trail, it starts and runs fine but stalled when going down a hill or if going fast and slowing down quickly.  I replaced the carb, fuel pump, air filter and drained and refilled the fuel tank.  The problem still persists.  After looking at several forums and YouTube videos, I adjusted idle, throttle cable switch on handlebar, and all carb adjustments.  Still having the same issue.  I have looked as replacing the carb one more however I don’t want to spend the $300 + price for a new OEM carb and there doesn’t seem to be a good aftermarket available given the reviews stating problems with all the ones I have found. On one occasion when working on the carb I dropped a screw down the intake neck into the piston chamber.  I removed the head retrieved the screw and adjusted the valves to .006 in clearance.  Everything works fine however the stall issue persist.

Any help will be greatly appreciated. Stan

Goodness Stan, it seems you have thrown tons of cash at the machine and it still will not play nice. I had a girlfriend like that one time, but that’s a different story. So, let us take one action at a time here and see if we can find the issue you are facing.

You say you replaced the carburetor, but you didn’t say it was a new replacement. A dirty or varnished ATV carburetor will stall and stutter when the gas is pressed because it’s not getting enough gas for the amount of air that is being taken in. So here is the first and most likely the most important question. Did you buy a used Carburetor for the Polaris? This is an important part of the equation here. If you purchased a used unit then you may have gotten someone else’s problems to add into your growing list. ATV Carburetors are semi-technical in nature, but not really hard to understand once you have dismantled a few hundred like I have. Most carbs that sit in rotting fuel will need a full clean out with a chemical solvent that removes the varnish. I typically replace the brass jetting inside the carb and most times the needle with its seat as well. This gets most of my older machines running quickly and at very little cost. The entire issue you are describing, again, makes me believe that the engine is starving for gas.

Adjusting all of those cables and things is just compounding the problem before the actual issue is resolved. If it were me I would get an OEM or Factory service manual and properly set each cable back to factory specifications. Then I would remove the brass jets and main needle jet (fuel control into the float bowl) out of the carb. Purchase the factory main needle and seat as well as the brass jets and reinstall. Add my favorite product, Ethanol Equalizer, to the gas tank with one gallon of ethanol free gas and run the engine until she is purring smooth. This doesn’t mean get out on the trail and dog the poor old man, but allow it to sit and idle for a time with a few twists on the gas here and there. The chemical has to work so be patient. This should get you back on the trail in no time. Just remember to be patient as this is a process not a race. It took SEVEN YEARS of sitting in crappy gas for the carb to get this way so it may take a few hours to reverse it all! One last thing, please, do not let it sit that long again. Your quad loves you and needs your attention at least every other weekend!