Well I recently became the proud owner of an 89 LT500. And let me just say, it is in great condition. I got it for a bargain price as well. The only problem is I have run it once since i got it and now it has a weird pulsating idle. it almost dies then revs then almost dies then revs...etc. Ive been told this is because its sucking in air from somewhere. but from where? where should I check and how can i check? Any help would be great. I love working on engines myself so i dont want to take this to a shop. Ive also been told that I should fix it soon because if it is sucking in air, it can melt the piston cause it'll run leaner. The weird thing is that it idled great when the guy sold it to me!!!!
Thanks guys. I look forward to your responses.

 

DO NOT ride that Zilla any more. It is so lean that it will melt down your piston for sure! That happened to me on my 87. What happened on mine was that I got a leak where the base gasket is. It just happened that my crankcase was somehow warped and I had to get it decked. You could check for a base leak this way, it's a bit of an ole redneck method maybe but it works. Start the bike and with it running spray either (starting fluid) around the base of the cylinder, it there is an air leak there it will suck in the ether and burn it causing the bike to rev up, get it? Be carefull though and good luck. Let me know what you find out.

P.S. It's not almost out of gas is it?

 

Thanks zillaman. I was hoping it could have been something to do with fuel mixture. the bike idled fine when the guy sold it to me but it didnt have much fuel in it. I mixed up a new tank full and its only half way through. I've heard about the problematic base gaskets so I'll be sure to check it out. But its just recently been rebuilt so I'll adhere to your advice and not ride it. Thanks heaps for your reply. you may have saved a brand new wiseco piston! [img]i/expressions/face-icon-small-happy.gif[/img]

 

You should have a leak down test performed on it. It is fairly simple to do so it should be fairly cheap to have done by a shop. If there is no leak detected, I have another suggestion. I had symptoms with my 'Zilla that mimicked an air leak but wasn't. The problem that I eventually found was that the carburetor slide needed to be replaced. The surface on the slide where the idle screw contacted it was worn to the point that it no longer held up the slide far enough. This caused the bike to almost die at one time and the race at another. I also had a very similar problem with a Blaster I used to own so apparently it is a relatively common occurance. Try raising the idle (screwing in the idle screw) and see if that cures the problem. If it won't screw in any more then check the slide for the wear I described earlier and replace as necessary.

 

Well it also could be the problem they are know for crank bearing seals. Air will suck in from there and casue the bike to idle up and down. Check the simple stuff first Is the carb cleaned pilot jet could be dirty. check all carb boots, head gasket, reed assembly and the base gasket.

 

Hi guys, Well i disassembled the bike last nite after i did that test you suggested. I started the bike and sprayed CRC around the gaskets. I smothered them and there was no air bubbles or no change in the bikes behaviour. Now i pulled the carby off to clean it and then took off the reed cage. I noticed that the reeds have two very small burn marks like its caught fire. There only about two mill wide, but on one side it has left a 1 mill hole that the reed cant cover up. could this cause the stoopid idle? the reeds looked pretty stuffed so im gona replace them anyway. Just wondering whether this could be the source of my problems. Thanks [img]i/expressions/face-icon-small-smile.gif[/img]