Have a 92 trailboss 250.
It will not start without choke and when it does you have to crank it for 30 seconds. Once running you can flick off choke and go right away and ride it. Will not idle and if you don't keep a little bit of throttle it will die. Then must restart with choke again and go. If to much load of the start will die as well.

Done
Rebuilt carb and cleaned it many times
New plug tried a few
New crank seals
120 psi compression when its warm

What am I missing?

 

Sounds like too much throttle slack and etc contacts may be touching in the throttle housing.Pull the sleeve back from the throttle housing and adjust the thumb lever play to no more than 1/8" free play and see how it does. If this doesnt help,do a compression check when cold.120 psi is on the low end for compression. This could be another reason it's hard to start.This is a common symptom when compression is getting on the low side.

 

When cold I am about 109 psi compression. Runs good when it runs just won't idle or start with choke off. It is touching I think inside the throttle. I will adjust it do it doesn't and see what happens.

 

What is good compression on a polaris opt? Manual says anything under 100 is not good

 

Think you found your problem.. 109 psi cold isn't good,should be at least 125 psi or more. Probably the main reason it's so hard to start.Sounds like time to freshen up the top end with a new piston and bore job. Just have the cylinder measured for the oversize piston needed.

 

How does that switch work in the throttle. No matter what I do if your not touching the throttle it is pushing that switch in. The quad will run if I apply slight pressure to the throttle and don't let it touch it.

 

Adjust the cable to where the throttle lever is snug,no slack like on the later etc throttles and see if that helps. The older style switches are different,just remembered.The electronic throttle control is supposed to limit rpm if the cable is snagged by a tree limb to keep it from running wild. Just a safety device.