Petcock.. Not working.

Ok the petcock on my 82 xj750j doesn't seem to be working, well it works but not correctly. The fuel will ONLY flow when the petcock is set to prime, it will NOT flow when it is set to on or to reserve which sucks because if i run out of gas there is no "reserve" tank to get me to a gas station. Now with that being said and the responses i had in my last post i'm thinking i may be missing a vaccum line or something. My question is this.. Is the petcock just bad?? or is it something else (clogged, or missing vaccum line)??

 

test the petcock, by putting the end of the fuel line into a can, with the tap in the on possition suck on the vacuum line & the fuel should flow & you should not taste fuel. have you checked that the filter in the tank is clear?

 

If you don't have a vacuum line on the Petcock running from the Vacuum Port to an Intake Manifold ... you need one!

Its a Vacuum Operated Petcock.

 

Yes, and note that fuel will only flow from the other positions when the bike is running...and vacuum line is attached.

 

Thats pretty much the answer i was looking for.. thank you.. now i just gotta figure out why there isn't one or where to run it to..

 

I got it figured already.. thanks guys.

 

You need about a foot of small vacuum hose.

On the Petcock there are two hose fittings.
The larger of the two is the FUEL -to- Carbs Outlet.

The smaller of the two is the VACUUM VALVE PORT.
Connect a length of Certified Vacuum Hose to the Vacuum Port on the back-side of the petcock.
Run the other end of the Vacuum Line to one of the Manifold Vacuum Port Connections on one of the Intake Manifolds.
Any one will do; but "Stock" is to run it to the Number-3 Manifold.

After running the Vacuum Line to the Manifold -- check to see that the other three Manifold Vacuum Ports are closed-off with Rubber Stoppers.

 

I ran it to the number four and it works fine now.. i don't know why the guy had it it disconnected.. thanks for your help though.

 

if your # 4 plug oils up you will know why.