When you say pilot valve, do you really mean the air screw (philips screw on the right side of the carb, on the outside) ?

Setting that is simple: turn clockwise until it is closed, then back off 1 1/2 turns to set the theoretical "correct" idle position. (If we can ever get the engine to idle, you will need to adjust further -- in very slight adjustments -- to boost the idle speed up.)

I had the same symptoms on my 88 Trail Boss, and confirmed it was too much air because it ran with the choke full on, but died with choke off. Fixed by the above procedure.

If you really mean the pilot valve inside the carb, I have not messed with that, so unable to suggest anything, but here is a link to the Mikuni VM tuning manual:

Mikuni American Corporation

The link you want is: VM "Round Slide" Tuning Manual

 

although my carb is basically like that one mine uses a pilot starting system that bypasses the throttle rather then a choke. the pilot valve is a plunger type that opens and closes to allow fuel and air into the engine for starting the engine.

 

new update and hopefully a good one. i don't really know what i did but cleaned the carb again, put in new plug and cleaned the electrical terminal. when i turned the key it fired right up and idled real nice sounds like it has enough power to out run my 400 suzuki. thought the coil or the cdi box may have been bad but they seam to be working correctly. as soon as the garage warms up a little (i lit the pellet stove) i'll finish putting it together and take it for a ride. hopefully my problems are solved for now.

i just want to thank each and everyone who not only replied to my problem but those who just looked in to read my thread. without the help and support everyone gave me my Trail Boss would be just another yard ornament.

 

Thanks for the "thanks" over the years we all have had questions and all had to learn. Without the help of others, trying to figure out the problems on our own would just end up costing a lot of unnecessary $$$ happy to hear your on the right path to getting the quad going.

 

Good to know trees, congratulations, sounds like whatever you did chased the last gremlin out of there.

Enjoy !

 

took it for a ride. it's covered with mud now. ran good just need to tune it up.