Quad was sitting for 2-3 years. I put sea foam in tank, removed fuel pump and cleaned carb, it started and died when I rev it up. cleaned carb again, would not start. put new carb on, drained all fuel out. Put new fuel in. Know it backfires out exhaust and sputters and sometimes backfires out the intake.
Need Help Please

 

Not singling you out,but another post where owners have gone into carbs two or more times cleaning and not replacing parts. Not necessary,plus no need to buy a new carb(unless the old one is trashed out) especially if it's one of those cheap Chinese knock offs out there. The BST40 Mikuni is a good carb,but the most common problems was fuel leaking past the needle seat o-ring and also adjusting the float level correctly.The replacement carb you have may not have the same jetting also,some have found trash,metal shavings when the removed the float bowls.Install a good carb kit on the oem Mikuni carb.https://www.ebay.com/itm/Polaris-Spo...!US!-1&vxp=mtr Look at this article on the BST40. A little different than yours,but goes into good detail on the float adjustment.The BST-40 Bible | Adventure Rider This may not be all your problems but at least you can usually eliminate the carb from the list. Other things to check is to pull the fuel line from the carb,crank the engine over to see if you have a good steady stream of fuel from the pump.If you don't have,fuel pumps are cheap(8-12 bucks) on ebay and amazon.Check the valve clearance. .006 intake and exhaust. New plug,air filter if needed also. Also sitting up for two years,feel the exhaust flow. Dirt dobbers as we call em down here(wasps) plus mice love to make nests in places like this. If the problem is beyond the carb and fuel system,could be electrical. Here's cheap 5 buck manual that can help you narrow things down. http://polaris-atv.brssm.com/2002-Po...ce-Manual.html