Gas not flowing to carburator I took petcock cover out and found that gas had stayed there and became gummy I cleaned it but feel there might be more in filter motercycle stays on but not allowed to acelerate. Is it dificult to remove the petcock from tank? Are there any precautions I should take when attempting to remove it? Thanks RJ

Sounds like the gas tank may have some crud in the bottom that is prevent the fuel from flowing through the petcock.. OR the petcock itself is stopped up. Make sure the petcock is not stopped up first.. then make sure the tank is clean. My personal ATV went through this very thing...the TANK and the PETCOCK were stopped up.
You are going to have to remove the gas tank to do this,
BE CAREFUL!!!!

Yea these carbs can be a real pain sometimes to get right. First thing you need to do is varify the float seat is working and totally stopping all fuel flow.... and all the jets, main, pilot and choke circuit are absolutely clean. Bench test the float needle valve by connecting a hose to the carb fuel line nipple and letting gas gravity feed as it would in a run position. if it tests ok, remount it on the bike...
i'm guessing you have a vacuum petcock on this year model? If you do, it needs to be inspected.
In the "on" position you should have no gas flow coming through the petcock, In the "prime" position it free flows. If there is a hole in the diaphram the engine will **** gas and not air (vacuum) through the hose and it will flood. If you don't have a vacuum line on your petcock then it is a different kind. Be sure to check your crankcase, it could be way past full with gas that has entered, dont start your engine like that...drain it all out. make sure the air filter is dry. You will have to replace the spark plugs...a gas soaked plug won't fire.
Good luck, i hope this helps.

The fuel petcock for your gas tank has a vacuum bladder in it. If there's no engine vacuum, fuel is supposed to stop flowing out of the tank, preventing carb overflow and accidental draining of the tank. However, once the engine starts, fresh gasoline will begin to flow out of the tank into the carbs. I believe but am not certain anymore that the vacuum cutoff mechanism is disabled when you turn your fuel petcock to "prime" or "reserve." If that is correct, you should be able to duplicate the carb overflow with the petcock in one of these positions.

As for the specific cause, it sounds like one or both of your carb floats may be sticking in position, preventing the fuel shut-off needle from seating correctly. This can easily happen if you haven't ridden the bike for a while--the most volatile compounds in the gas in your carbs will evaporate, leaving behind an increasingly gummy and sticky substance that will eventually harden into varnish if it's not cleaned out. That gummy stuff seizes up the pivot points for the carb floats, so they don't move correctly. Gummy gasoline residue can also build up over time, even if you ride the bike often, though this usually happens after the bike has been sitting. The fix for this is to clean out your carbs. On an early (1982) GS450, I was able to do this once by removing the carb bowl without removing the carbs from the motorcycle and spraying the float pivot points with a heavy-duty gum cutter (Berkebile 2+2--it's like carb cleaner on steroids, but it will also damage paint).

By the way, if I remember correctly, your carbs have a crossover tube to ensure that both carbs have the same gasoline level in them. This keeps the fuel mixture even for both cylinders and keeps the engine running smoothly. However, that also means that a single carb with a stuck float will flood both carbs equally.

Typically there is a vacuum fuel petcock involved. When the motor is turned over a small vacuum line opens the fuel petcock and fills the carburetor with gas. If the vacuum line is not hooked up correctly the fuel will not flow when vacuum is applied. If the petcock is stuck, the fuel will not flow. Also if the carburetor has been sitting with old fuel in it for a while the float needle may be stuck closed stopping fuel flow. Clean the carburetor and inspect the fuel petcock for operation and correct hook up.

The carburetor may have inhaled some trash, debris or parts of fuel line. Remove the cover on it that does not have the vent-hole in it. Inside on the carb body you will see a very small fine-mesh filter screen. Make sure it is not covered with debris. If so, clean it up and replace cover. This commonly gets dirty and needs to be cleaned after lines deteriorate.

On the top of the carburator there is a needle valve, closed by the float lever. 
If the carburator chamber is full with gas, the valve is closed and no more gas can enter the chamber.

If the chamber is empty and no gas flows inside, the valve may be stuck in closed position. Cleaning or some sharp (but not very hard) knoks on chamber cover may help.

Some times the float gets broken and falls down. This is a bigger damage, because it may lead to carburator overflow.

Inside the large cover at the bottom of your carb is a flotation bulb which controlls a small metal rod with a pointed end which opens and closes the flow of fuel.Dirt or gummy deposits stop the closure and allow fuel to flow freely through the engine.If your a handy type remove the carb and take the large cover off the carb remove the float and the "needle valve and clean the tip of the valve and the narrow hole the valve goes in with carb cleaner and small brushes.If not so handy remove the carb and take it to a knowledgeable neighbor or repair shop. If you do the work yourself take digital pics of the process to help reassembly.

Check the feed pipe for gas from the tank to the petcock and thn frm petcock to the carburators, probabely it may have clogged with rust having stayed tht long .
You can also by pass it and fill the carburtors with gas and thn try to start it .
After trying to by pass the petcock and still you dont get gas into the float chamber thn you will have to clean the carburator there may be obstruction (dirt ) around the float pin.

Hope this helps!.

Knight (yamaha XJ750A 1981)