my freind bought a 98 zr500 and when we test drove it , there was no bottom end and backfiring out the exhaust. we found the pistons were very worn ,they actually had a ridge along the crown.we put in new pistons, cleaned the carbs, checked the reeds everything was ok . the machine has a very bad hesitaion on the bottom end .if you pin the trottle it almost dies before it revs up.the engine seems to idle fine so i dont think the crank seals are bad ,also the old pistons showed no signs of running lean. one thing we did notice was that the mag side carb has a lot less vacum to it if you put your hand over the bell .we checked the fuel pump and pulse line and they both hold a vacum so the only thing i could think of is a leaking crank seal; on the mag side. any ideas. once the engine is reved up it seems ok but we havent driven it yet under load. could a bad stator cause this?

carbs adjusted properly??? I would check the carbs one more time,,, I have cleaned them before and put them on to have the same problem,,, just to pull them and clean them one more time,,,,
any way to tell your exhaust gas temps as your trying to throttle it and its bogging??? is one side hotter than the other??

thanks for the input puree, everything is ok the weak vacum signal was the slides were a little off. i cant beleive how much of a difference between the carbs there was for the difference in slide position. they were out maybe 1/32. anyways pressure tested the engine all ok checked the stator, nfg no reading on my ohm meter and when we pulled the mag off you could see the green wire was burned right off the coil. im surprised it ran

but it ran, and thats all that counts,,, other than the fact that WE NEED SOME SNOW!!!!!