What would cause a 85 yamaha big wheel to run for about 20 min then die and not start for about another 20 min?

it sounds like either the fuel filter is clogged or choke is stuck

carb needs overhaul or high speed jets need ajustn--hav a pro du this cause if u lean it out too much-u can fry the engine--clymer makes a mechanics manual for motorcycles and atv

Hi L.A, TURBO,I got a 85 silver nissan 720 4x4,see my icon,here's a link to a channel you should join,it's a site for nissan 720 owners,you can post problems and they will get solved,it's free,you can sell and buy parts,post pictures,see other 720 owners trucks,very cool channel. look me up,it's Tommy perkins,go to my page and see my pictures,had my truck for 20 years.Are you having carb. problems,our 720's carbs go out and we replace with webers,here's my conversion.I had problems with it and they have to be replaced.

if you need to keep your foot on the gas to keep it running clean the throttle body and idle speed motor

Well if the Durango starts and runs for like 15 mins and quits then won't start again untill it has cooled off a bit I would be checking the crank sensor and the pick up coil. If it starts then dies right away but will run if you hold the gas I would clean the throttle body with carb cleaner and make sure to clean around the butterfly edges inside the throttle body.

Those rattly noises are detonations,  caused by a very lean mixture. All the other symptoms indicate that the fuel flow to the carb is too low. Since you have replaced the pump and the filter, the only other things left to check are the lines and the tank sump. Or you could install a much larger pump.

POSSIBLE CAT CONVERTER OR FUEL FILTER ISSUE, MAKE SURE THE MASS AIR SENSOR IS CLEAN,USE BRAKE OR CARB CLEANER,AND AIRFILTER IS CLEAN WITH NO BLOCKAGE IN AIR BOX. GOOD LUCK.

battery is very low I aqssume from trying to start it so many times. have the ignition module checked out
that maybe your problem if its very old. it is located inside the distributor

If that is carbureted, and has a mechanical fuel pump, try running a length of fuel line from inlet side of pump to a gas can that has fresh, clean fuel, and if it runs good that way, you know problem is most likely in the tank. Removing the tank & cleaning it out is best solution from there. I'd even be tempted to add a small bottle or 2 of Lucas Fuel Sytem Cleaner to first fill in clean tank, just to help clean lines as well as carb.

I had a similar problem and it turned out to be the rubber fuel lines being old and cracked. The hoses would warm up and fuel would squirt out of the cracks. I had to replace three fuel line hoses and it has been running great ever since. Good luck.