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Here is my problem:
I have a 1981 yamaha xs400 special 2. I bought it used last July and it has about 15,000 miles on it although, I have only put about 5 or 6 miles on it myself simply because it isn't ready for the road yet. Sometime last August, I had the carbs professionally cleaned, synced and reset. Just before I stored the bike for the winter, i tried to start it one last time. When it wouldn't start, I opened up the carbs to take a look and also drain the fuel from them. When I opened it up, the same brass plug had loosened itself somehow from each carb. I filled the tank and put in the stabilizer, then left it for the winter. In the spring, I screwed the brass plugs back in and noticed that my tank was about 1/2 empty and there was gas all over the air box and surrounding area. I cleaned off the gas and tried to start it. the bike would start but it would choke out and stall if i pulled the choke, or if i wasn't giving it gas. I drained out the old gas and put in fresh premium, changed the spark plugs and tried again. Same problem. The last time i tried to start it, a hissing noise came out of the carburator/ airbox, and steam of some variety came out of the airbox. I thought maybe a fresh oil change might help, so i drained the oil. What came out (I'm assuming) was a mixture of gas and oil, since i got about 3x the liquid out of it than i should have. I put in fresh oil and tried to start it again. Only this time when i went to kick it over, there was absolutly no resistance in the kickstart. I could turn it by hand with no effort. Before the winter, the bike ran great, and had great compression. I have heard that a leaky petcock can be the cause of this problem. What do i do now? Any suggestions?
Thanks,
Jason

It takes a leaking needle vavle and a leaking petcock to get that much gas into the crankcase. I'd take it back to the 'pro' who did the carbs and tell him what happened. He shpuld realize the problem and fix it gratis. If he doesn't, inform him the needle are leaking and have him correct the problem.

These brass plugs that came loose.... where they inside or outside on the carbs? It almost sounds like the needle jets were never tightened in properly, and that could cause your symptoms.

The brass plugs were inside the float chamber of the carbs. I believe that they were covering the pilot jets, but i'm not positive. I would have to take it apart again and look to be sure. It could also be the main jets.

Thanks,
Jason

Unless it's the choke jets, all jets should be tightened enough not to move.

Pull the fuel tank off and see if the gas petcock is leaking.
Yamaha's in the early 80's had vacuum operated petcocks that would allow gas to flow only when engine is running or when petcock is in Prime position. I had to replace my petcock(1982 Seca 550) because in the on position fuel was leaking slowly, this could fill up carb and crankcase with gas.

thank you to everyone for responding. Does anybody know what kind of damage this could have done to my bike? Also, how should i go about ascessing the damage and fixing it?

Thanks,
Jason

Probably no damage to engine but if gas was in your oil....make sure you change both your engine oil and filter, after you have replaced the leaking petcock.

This usually happens after the bike has sat a longtime. What is happening is the float is set wrong, and never lets the gas shut off, overflows forever, and goes into the oil. Just put the dipstick out and smell it, if it still smells of gas after the float ajustment, bad needle and seat.

Thanks to everyone for responding, i replaced the petcock and took my carbs back to the shop that did the work on them, they checked them out and said that they were set fine. I figured out my compression problem, my clutch was slightly engaged and when i looseded the tension at the handlebars, i regained compression. I have a new problem though. About a week ago i changed my oil and refilled it according to the specifications in my manual like i always do. The bike sat for about a week and yesterday i went out to start it up, and my oil pan was dry! I could see all the way to the bottom of the pan! There was no puddle under the bike, and when i drained it a week ago, i got slightly less oil out than i put in. Where is my oil going, and how do i fix this problem?

Thanks,
Jasson

Oil Gnomes?????

Seriously ... are you absolutely positive you filled it up?