Start at the beginning... Look on the cylinder base.If you have a 500 engine it will show .498L If it is a 500 and you bought one of those Chinese knock off carbs on ebay they're a clone of the Mikuni BST34 that the 500 used up until the 2000 model,not the BST40 that should be on the 2002 HO 500. If it was a 400 engine it would show .0425L on the cylinder.If the frame show a 2 on the 10th digit then it's a 2002 model. If you happen to still have the recoil sticker still on,the first two digits of the serial number is the year model of the engine also.Confusing,yes it can be when you buy a used machine. Plus to add to the confusion and probably your problem, the 2002 500 used two different stators and two different flywheels according to engine serial number.http://www.cyclepartswarehouse.com/o...to-all-options this could be the difference on the regulator also. Plus even Ricks shows the two different stators for this split year model. https://ricksmotorsportelectrics.com/results/