XJ750 Maxim fuel flow question.

Hi everyone, this is my first post so I hope I don't mess it up. I bought an XJ750 Maxim about a week ago and it has been sitting for about 10 years or so. I flushed out the gas tank and it had very little sediment then I drained the bowls on the carburetors. Everything I drained the fuel was surprisingly clean. I took the petcock off and it was not plugged and the screen looked like new. When I turn the fuel on I get no gas through the filter and it's open and so are the fuel lines. I have to turn the gas on and open the drain screws on the bowls before the gas will flow. It does run pretty good for a few minutes and then it's out of gas again. Any ideas hoe to solve this? Thank You.

 

The Yamaha petcock is vacuum operated and won’t flow fuel in the run position unless the engine is running.

if you indeed have the correct petcock it will have three positions: REServe, RUN, and PRIme. PRIme allows fuel to flow into the float bowls with the engine off.

please report back with what positions your petcock has.

 

Thanks k-moe, The petcock has off, on and reserve. I guess that's not the right one?

 

Does it have a vacuum line, or a fitting for a vacuum line, on the back?

If not then you have a non-vacuum petcock, which will work fine. We just need to know so we can troubleshoot appropriately.

 

It has the fuel line nipple only. No place to attach vacuum hose.

 

Ok. That rules out a faulty vacuum valve.
Open the gas cap and see if the float bowls stay filled while idling.
If the gas cap vent is plugged there will be a vacuum formed in the tank, shutting off flow to the carbs.
Your Gas Cap and You

 

I will give that a try when I get home tomorrow. Thank You.

 

The bowls are full of fuel with the cap open and engine idling. I used a little compressed air on the gas cap in the hole and shut the cap. It ran for several minutes that way so I think the problem is solved. I feel like I wasted your time with something so simple. Thanks again k-moe.

 

Not a time waster at all.