hi ive got an 87 lt500 that im having a lot of trouble with, i need to know the torque on the head studs, its been bored 40 over,ported,and the head was shaved,has wiseco piston,ive got the air screw turned 2 turns out and it get spark knock bad when i get on it in the upper rpm range does anyone know what the main jet should be? the crank bearing is good and it just sounds like a hard knocking ,maybe detonation?and the power valvhas an adjustment thing on the side and it is about a quater inch away from the line i think its supposed to point at,i dont know though, any help would greatly help me thanks Brandon

 

A few questions, did you just have it ported and have the head shaved or has it been like that? A lot of times a ported motor will need to run on 100+ octane race fuel as opposed to pump gas. As far as your main jet goes just go keep going up in size until your quad starts to miss from running too rich and then go down one size, or two sizes depending who you ask. But you need to remember that your main jet only effects 2/3 to full throttle, your pilot and needle jets do the rest.

 

I suggest that you get jetting and octane recommendations from the performance shop that did the work. I am guessing that since you don't already have this information, you bought the bike already ported and shaved. Try to track down the shop through previous owners. If you are unsuccessful, do a compression test and note the reading down. Call any reputable performance shop and get some rough jetting and fuel recommendations from them. These shops don't like to give out free information so your best bet is to make a purchase first before you ask for technical assistance. A better route to go may be to get a hold of a tech line for the aftermarket exhaust you have (I assume that you aren't running the stock exhaust with a ported engine). Whatever way you decide to go, discontinue riding that quad until the problem is remedied! Those noises aren't just annoying, they are ruining the motor and will soon end in a piston roof with a skylight!

 

it has an lrd adjustable pipe and the motor work was done by vitos it was like that when i bought it. the guy i bought it from said to run 20\1 gas oil mix but i thought that was to rich so i ran it 50/1 maybe its jetted to be ran richer, it stumbled on low end so i moved the needle clip position all the way up and turned the air screw 2 turns out and it runs a little better.ive already melted one piston so i know its running a little lean,melted the rings right to the piston. most two strokes smoke when they are idling and you gas it but this dont.any more suggestions will help thanks

 

If it was jetted to run on 20:1, and you are now running 50:1, then you are richer than you ought to be. If I understand correctly, you have the needle clip in the top position? If this is the case then you are at the leanest setting there as well.

Do a leak down test.

Don't mess with the powervalve timing adjustment. Set it per the service manual and forget it. The head stud torque can also be found in the service manual. I can look that up for you this evening when I get home (I don't carry my service manual to work) and post in the morning. Someone will probably beat me to it though.