Fuel tank petcock

[Racer71]

On a 1989 Honda Elite 50 SB50P, my petcock has two lines coming off of it, is one for vacuum and the other for fuel?

[zz28zz]

Correct. Vac line goes to intake and fuel line goes to the carb.

[Racer71]

Thanks zz28zz, but what I need to know is if it needs vacuum to open the fuel flow, if it does mine is no good and I bought it from a honda dealer a few months ago, do thes things go bad often?

[zz28zz]

Yes, when eng is running, there's a small amount of vacuum in the intake where the vac line attaches. That vacuum opens the petcock and allows fuel to enter carb. When eng shuts off, there no more vacuum, so petcock closes.

I recently bought an aftermarket replacement petcock since mine had old gas in it for years. I was surprised by how little vacuum it takes to open. Can be done by mouth no problem. I assume the Honda petcocks don't take much vac to open either.

They usually don't give many problems but if fuel was left in tank for a long time, they can get gummed-up. Occasionally they will leak fuel into the vacuum hose if the diaphragm inside ruptures.

With yours being new, it shouldn't be gummed-up. Are you sure the lines didn't get crossed?? It's not really obvious which port is which to the untrained eye.

[Racer71]

I really appreciate your help, the fitting closest the tank is fuel to the carburetor and the bottom fitting is vacuum to the intake manifold, but what is confusing to me is that I just disconnected the hose from the carburetor to drain the tank and the fuel all drained out, I thought there had to be vacuum for the diagram to open and let fuel run out?

[bonesv]

I really appreciate your help, the fitting closest the tank is fuel to the carburetor and the bottom fitting is vacuum to the intake manifold, but what is confusing to me is that I just disconnected the hose from the carburetor to drain the tank and the fuel all drained out, I thought there had to be vacuum for the diagram to open and let fuel run out?

Then that means it is a bad fuel petcock and you should replace it or install a valve to which you could shut it off when you aren't riding it. If it runs fuel into the motor when you stop the motor, then you also have a bad float needle in the carburetor, which you should certainly need to replace asap. Hope this helps you.