On choke will idle but immediately stops when i put it in gear

Hmm...........
1985..........
Probably carb? Automatic choke not working? Remove air filter and spray carb with cleaner, Make sure all parts move freely. With engine cold, check automatic choke position. Start and check function as it warms up.

Check your base gasket on the carb.

Hi. Maybe a vacuum leak or a auto choke issue keeping the idle high. If the idle is too high then the reverse gear will crunch.

You need to check the cold choke set up, which may be called a IAC
Idle Automatic Control this is sensor works the am starts for cold or hot idles...
Do you have a light on??

get carb cleaned--purchase a haynes or clymer manual for procedure

Check the muffler to make sure that the spark arrestor screen is not plugged. Make sure the air cleaner is clean and not plugged. Turn both L and H mixture screws CW to stops (lightly), then back out 1-1/2 turns each. Warm up the engine, then open the throttle and turn the H needle CW until the engine speeds up, but still '4-stroking' but should immediately start '2-stroking' with light cutting. Release the throttle and adjust the L needle CW for fairly smooth idle, yet rich enough to allow the engine to 'follow the throttle' immediately when accelerated. Adjust idle speed CW until the chain starts to turn, then back off until it quits turning. Make sure the chain is being properly oiled and is adjusted for no chain droop, yet turns freely by hand. Hope this helps!

wrong jetting can cause reving up buddy also the backfiring is due to too much fuel going in the engine on the carb is a screw mixture screw turn this in 1/4 of a turns at atime until it stops back firing also has the bike been rejetted before buddy

While at the river try to adjust the fuel air mixture. When you are on the water it puts the engine under a load and if that dont work then dont be afraid to bump up the idle stop screw slightly.

auto choke cold start device

sounds more like the IAC, Idle air control valve.. they can be cleaned with carb and choke cleaner gently...