My 1994 Yamaha YZF750R started running kind of rough and back firing. I put some sea foam in the tank and it started running worse, most likely loosened up whatever was gunk ed up. I then warmed the bike up and ran it through the fuel line out of the bottom of the gas tank. Let it sit for five minutes and cranked it up again with a huge amount of grayish smoke coming out. It didn't back fire for awhile, but started doing it again but is running a lot better, another problem that resulted from this is when I put it in the tank the gas light stayed on, and when I ran it through the fuel line it went off and hasn't come back on, I've run out of gas on the highway twice. I'd like to stop this from happening in the future.

SOURCE: dead pw 50 and sad boy.

Many things could cause the problem. Let me see if I can help out.
You have spark, but is it enough spark? A weak battery can rob power from the coil so only a weak spark is present. Get a new stock NGK spark plug to eliminate the possibility of a problem plug.

It is good that you cleaned the carb because that would be my second target. Reset the air and idle screws. IMPORTANT > do not tighten these two screws down. Only screw these in until they LIGHTLY seat. Now turn each screw one and one half turns outward. Clean or replace the air filter and be sure the bolts are tight on the carb manifold. INSTALL AN IN-LINE FUEL FILTER. Let the float bowl fill then start the engine. Set the idle speed with the idle screw.

Remove the cylinder head. run the piston down to the bottom of the cylinder. look inside the cylinder. On th carb side (intake) you will see an intake port > a large hole that lets gas into the cylinder. Now look at the exhaust port. It is possible the exhaust port is pretty plugged up with carbon. The intake and exhaust ports should be approximately the same size. Are they? If not then remove the muffler and take a screw driver and plastic hammer and knock the carbon into the cylinder, thus enlarging the exhaust port to its' proper size and allowing the exhaust gases to escape. Vacuum the carbon out of the cylinder. De-carbon the piston top and the cylinder head.

Get back to me and tell me what you find. If more is needed we will go further.

SOURCE: will not start turns over ok but will not fire up

during the winter you can get build up on the tip of your spark plug that will prevent the engine from firing. remove the spark plug and soak it in gas for ten minutes or so. Dry it ogg with a clean towel reinstall it and it should start right up.

SOURCE: 2007 yamaha virago won't start - replaced spark

it's not that your not gettin gas it's that the gas is not getting thru the carbs to the engine. your bike will probably start w/choke on and then die, your jets are clogged and happens to most bikes that are stored w/gas in the carbs.,,,clean them if you know how or take it to a trusted mech...good luck to you...Tim

SOURCE: Yamaha TW 200 starts but won't run.

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"..

SOURCE: yamaha yzf750r missfire rough running

Try taking air cleaner off before going to far, Blow carbies with air, dont use full force I done this to mine and it fixed it you may be lucky dirty jets.