Hello All,

I am restoring an old Yamaha XS400G 1980. I think ALMOST everything is in working order, but I am having trouble with fuel flow. If I set the petcock to the prime position for several seconds then switch it to on or reserve the bike will start/run no problem, but then die after a minute or so. When I try to start it up again the bike wont start until after I have 'reprimed' it for several seconds. I went out and bought a inline fuel filter so I could actually watch the fuel flow from the petcock to the carburetor and when the petcock is in the on or reserve position I see no fuel flowing. (The inline fuel filter is see through).

My guess is that the petcock is damaged and fuel cannot flow in the ON and Reserve positions. Any advice?

Thanks,

Adam

Hello All,

I am restoring an old Yamaha XS400G 1980. I think ALMOST everything is in working order, but I am having trouble with fuel flow. If I set the petcock to the prime position for several seconds then switch it to on or reserve the bike will start/run no problem, but then die after a minute or so. When I try to start it up again the bike wont start until after I have 'reprimed' it for several seconds. I went out and bought a inline fuel filter so I could actually watch the fuel flow from the petcock to the carburetor and when the petcock is in the on or reserve position I see no fuel flowing. (The inline fuel filter is see through).

My guess is that the petcock is damaged and fuel cannot flow in the ON and Reserve positions. Any advice?

Thanks,

Adam

is the vacuum pipe connected to both the rear of the petcock and over the frame to the carb inlet?

is the vacuum pipe connected to both the rear of the petcock and over the frame to the carb inlet?

I think I am about to seriously embarass myself, but hear it goes.

The petcock has two hoses coming out of it. I attached the larger of the two to the carburetor. I assumed the other hose was for gasoline vapor. Is it supposed to attach to something? Where would I attach it?

Thanks for such a quick response!

Adam

is the vacuum pipe connected to both the rear of the petcock and over the frame to the carb inlet?

Where would I attach it?

On the left carb holder- the same port used to balance the carbs...or the right, doesn't matter- whichever one the tube reaches to easier.

On the left carb holder- the same port used to balance the carbs...or the right, doesn't matter- whichever one the tube reaches to easier.

Ah. I was looking for an unused hole somewhere on the carburetor. Thanks. I suppose the air rushing into the engine from the carburetor creates a vacuum which activates the petcock.

Thanks,

Adam

Ah. I was looking for an unused hole somewhere on the carburetor. Thanks. I suppose the air rushing into the engine from the carburetor creates a vacuum which activates the petcock.

Thanks,

Adam

Correct. Make sure whichever one you are not using is capped.