petcock problems prompt post

Last night I cleaned and oiled my UNI air filter. Of course, I had to pull the tank to get to the filter housing and now I'm having problems with fuel delivery. In the process of removing the tank, I disconnected the fuel line from the petcock in the "on" position, and everything was fine. No gas leaks. I let most of the fuel from the line and fuel filter run out into a can. When I finished with the air filter, I replaced the tank and reconnected the fuel line and set the petcock to pri. Some fuel ran into the line, but did not fill the fuel filter. (though the filter was full before removing the tank) It only filled the filter about half way. Now I can only get about a mile before the engine sputters out. I have the petcock set to reserve. (I have about half a gallon left in the tank) When it cuts out, I set the petcock to pri again and it delivers a bit of fuel to the line. It starts with no problem and I can make the mile ride back home. I've never had this problem before, but this is the first time I've removed the tank and had to rePrime the fuel line. Am I missing something here? When set to pri, I can see the fuel rush into the fuel filter for a few seconds, then it seems to just stop flowing.

 

A couple of initial thoughts. Could there be an issue sending fuel down the line in pri with only a bit of fuel in the tank? Perhaps the extra weight of a few gallons of gas might be enough to fill the line. Also, I've never gone for more than a couple of miles on res, so maybe there's an issue with the res position on the petcock, but not the on position.

 

here is a dumb question but did you remember to hook up the vacuum line from the fuel valve to on of the intake boots? This would also cause no fuel to flow with the valve in the ON position. Sorry this is the service tech side of me coming out lol. Also there could be some stuff clogging the screen filter inside the tank at the reserve level.

 

XJDriver, thanks for the response. When I removed the tank I only disconnected the fuel line from the petcock. I was careful not to loosen anything else. (except for disconnecting the wiring clip for the low fuel light) So I don't think that's the issue. Though it's possible that I may have jarred something loose in the process. I'm just about to run to the store to pick up a new fuel filter just in case the bit of sediment in there shifted and clogged it. It is possible that the screen filter for the res position is clogged, but would that also keep the pri position from working? I could be wrong, but I think that pri draws from the reserve level.

 

If the petcock is a vacuum type there should be two pipes, one for the fuel and one cconneted to one of the inlet rubbers, between the carb and head. This provides the vacuum to operate the tap.

hek this pipe is conneted to. It will give the problem you describe.

 

I'm a dumb***. I guess I pulled the tank without even noticing the loose hose. I was a little suspicious when I found a stray butterfly clip on the ground, but I didn't know if it came from my bike. Good thing I kept it. I bent the clip a bit to tighten it, reattached the vacuum hose and... voila! Runs just like she ought. Mechanical malfunction of the brain this time. Thanks for your replies!

 

i just bought a 1982 seca xj750....it was running when i brought iit home and shortly after it stopped.....are my carbs clogged up or what??? can anyone help?

 

How long had the bike been sitting prior to you buying it? Will it turn over and at least attempt to run? Can you start it if you use starter fluid/carb cleaner? I would do the following for a bike I just purchaced: Change the oil and filter, clean the carbs and sync. compression test the motor and also when you get a chance, check the valve clearances. The first two I would do as soon as I could, especially since the bike was running and now its not. There are other things you could do that others will chime in on. Congratulations on your new bike and welcome to the site