Sounds like you passed the leak down test. One thing that test won't find is a dynamic leak... E.G. crank seals leaking due to loose bearing inserts. The motor holds pressure when it's not running.
Have you looked at your crank bearings? It's a slim chance, but worth a look. (Take off your stator cover, grab your flywheel and agressively wiggle it up and down... ANY percieved motion means you have a problem)

The '87 carbs are known to be difficult to tune. (Junk) There are circuitry issues that were corrected with the newer models. The '87 carb has issues with mid-range lean spots that can be corrected, but it's cheaper to buy a different carb.
A high idle situation like your describing is caused from a lean condition... now it's just a matter of figuring out what's causing it.

good luck, and keep us posted?

 

i will check the carb numbers i know i am running a 350 main jet with all the jets for an 88 also i will check for the wiggle in the crank thanks alot also one other thing is it possible i may have a slightly warped head which could get wors when it gets hot but if that's the case wouldn't the leak down test let me know that ie it would leak from the head i will check these things on the weekend please check back on monday thanks alot both of you

 

alright i checked the carbs and they are both 43b10 which are the ones for my year. I took it out riding today and she was a pain in the *** to start every time i always pretty much have to put the choke up and she smells awful when she doesn't start up right away. Now for the problem

It was doing it again and i took it easy until i got back to my ride. When i got back there i put it in neutral and revved it up really high and kept it up there for a little bit. She stayed high so for a little too long so i tried adjusting the throttle screw but it did not help then i tried pulling the kill switch and she would not shut off so i switched off the gas and still she was going crazy so i pulled the spark plug cap and she was still running. She finally shut off after about 5 seconds with no spark plug cap on it. I know i have a lot of carbon build up on my piston.

Question: would the carbon deposits on the piston be a cause for the problem i have been describing to you or is that just another problem.

By the way i changed the hose clamp and checked out my reeds and repaired the small leak i had so now it holds 6 lbs for ten minutes or more (i only let it go for ten minutes)

Please help

 

on all the old mikuni carbs the slide tends to wear and get scratches in it, therefore pullin in exces air making the engine rev, if you can get it to idol this may be your problem, also affects the whole way the engine runs

 

i know this thread is old but I just got my newly aquired lt500 back together after a motor rebuild and I am having some similar issues. I can kick start it and the bike gets going with the choke out, rev it, try to start riding off with it and the throttle is very sporadic on me. very little throttle it wants to go, if i gun it the motor bogs down and hesitates, then when i close the choke the motor dies out entirely. I am stumped, and have already spent too much $$ at the stealer and they won't even work on my bike.

here's what I have done to it relating to the carb.


stealer took apart and cleaned the carb yesterday
brand new spark plug ngk
not running a filter in the box because the old one was falling apart and the box is completely clean, no debris.

 

i've come to terms that I am a complete newb with 2-strokes and carbs for that matter. realized I had the carb in sideways with the floats to the side instead of on the bottom side. anyway I changed the positioning of the carb and now I can't even get the motor to fire up! any ideas...?? or if your in the charlotte North Carolina area and want to come help, i will pay $$ and beer

 

I was reading this post and I thought , what about the rubber intake boot?It's definatly leaning out,the next time it does that turn the kill switch off and then open the throttle like your reving the engine.That will shut it down.I was told that too much carbon build up can cause that.Are the floats working properly in the carb?