What would cause a 85 Yamaha Big Wheel 200 to run for about 20 min. then die and not start again for about 20 min?

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

Check that the breather to the fuel tank is working and not blocked. Also check that the filters on the top of the fuel tap are clean.

Did the bike sit for a long while with gas in it?

What happens over time is the gas starts to break down (go bad).
When it does this, it turns into almost a varnish.
This starts plugging the holes in the jets, and the ports drilled in the carb, starting with the smallest, which is the idle circuit.

What is happening in your case is when you spray carb cleaner down the carb, it starts and runs on that, until it's used up.

You need to remove the carb and "boil it out" (clean and rebuild), paying attention to the idle jets and ports.

This diagram of the carb might help you:

http://www.bikebandit.com/houseofmotorcycles/2005-yamaha-yz85-yz85t-carburetor/o/m145327sch299511

Again, pay attention to the idle jet (pilot jet), #8 in the diagram, inside the float bowl.

did you replace all diaphrams in carbs and fuel pump ? balanced the carbs ?

carbs dirty with varnish--may need to overhaul--but 1st clean float area to eliminate any possible clog--get a repair book for carb maintenance and service

Two things:
1 Is fuel coming out of the fuel line. Older mowers have old fuel lines and they tend to get weak and collapse went they warm up with engine heat. Replace the old fuel line.
2 deposits in the carb. take off the air cleaner, start it up and spray a good carb cleaner in the carb until the engine dies. Put some 'seafoam' in the gas and a little in the oil and put the air cleaner back on and start the mower and mow on FULL THROTTLE. this should claen out the carb. Yes the mower will run rough for awhile.

these two cheap fixes will solve 85 % of carb problems. GOOD LUCK

During the time that the unit is malfunctioning, take a spare plug, pull one wire, and see if you have spark. Typically you would not have spark, based on heat saturation.
Also, check the plugs for over rich condition, but I suspect ignition. Doc

Look its really hard to tell without seeing the bike when it happens, and if im wrong just repost the question, but it sounds like a problem with the vacumn fuel tap.When it stops can you place the fuel tap on pri between on and reserve and see if it makes a difference


a hole in one float would not stop a multi cylnder bike, it would just make that carb flood

probably not the pick up coils as there are two and they wont fail together, and then come good again

Thanks for the extended question, much better than "my bike stopped whats wrong?"

If the bike has sat for a long period of time without being run - the gas that is sitting in the carb(s) will shellac.. Then the carb(s) would need to be cleaned and "rebuilt"..

v\:* {behavior:url(#default#VML);} o\:* {behavior:url(#default#VML);} b\:* {behavior:url(#default#VML);} .shape {behavior:url(#default#VML);} 285 7772400 10058400 259 261 257 280 262 283 1 06WOHFQ%ZQT6,!3GM2\Y["P 5 1 0 286 False 0 0 -1 304800 243 True 128 77 255 3175 3175 70 True True True True True 282 134217728 1 3 -9999996.000000 -9999996.000000 8 Empty 16711680 52479 26367 13421772 16737792 13382502 16777215 Bluebird -87325200 -87325200 (`@````````` 267 263 5 No. It sounds a too simple, but try this: The next time you run it and it starts to die, loosen the gas cap. It should start to run again. This means that the gas cap is clogged up with dirt. It is not vented properly, causing the carburetor to not get gas.

Jim