1986 300 bayou takes off when you put it in gear,h...

Greetings, I read your question and I think heavy-equipmentmanual.com can help you in this. Here's the site link - https://www.heavy-equipmentmanual.com/

Have you tried to lower the idle? When an Auto/5speed shiftable transmission is stopped in gear the drivetrain holds it back or loads it down a bit. If you take off a load the idle will rise. Sounds like your idle is too high. Do you have your idle set high to keep it from stalling?

Hi the cable needs slack if you take all the adjust out meaning the is no free play in the cable your taking the pressure off of the clutch plates causing it to not be engauged.

Could be an electrical problem. If it doesn't sense the neutral position signal it will not go into reverse. If your neutral light comes on then it may be a loose connection after the light. This is on of a few things to check out first

The first things I would check are seized brakes and then transmission condition/fluids. The auto has 2 clutches I believe. Make sure everything is full on fluids

Maybe time for a clutch rebuild. Loosen nut on right cover, hold in place, run screwdriver slotted bolt in until it seats then back it out 1/2 turn, hold screw in place and tighten the nut!

Make sure the needle/seat spring is still there. also make sure your fuel filter is clean enough to keep up to your carb's new thirst

do you mean the idle air fuel mix screw adjustment? its 1.5 turns out.

I am not really understanding what is going on...
.. OK...With ALL the clutch components and the drive chain removed - can you (in each gear) SPIN the main transmission shaft ALOT( 20+ turns) in the correct (drive) direction?..I think its counterclockwise.

It is important to remove the drive chain and all clutch components to do this check. You are checking for a SINGLE CRACKED GEAR TOOTH .. the crack will be at the base of a tooth.

Do this check exactly as described.. you are checking the functionality of the transmission alone. - no clutch-no drive chain. If you do have a cracked tooth, the transmission will only rotate about 340 degrees in either direction.
If it was the clutch giving the problem, it would happen in ALL gears...

After the check.. repost and we'll go from there.

What type of fluid do you have in there? in some cases we have put synthetic or oils with additives and it has caused the plates to slip.