Petcock issue??

[micallen]

I finally found out how far my bike will go on a tank (159.1 miles BTW) and flipped over to reserve.  I finally got it to crank, but it ran ROUGH!!  It sounded like I had 2 plug wires pulled or something.  It was rough and backfiring.  I had to keep it reved up, or  it would cut off.  I swung back around and filled the tank up.  Turned the petcock back to ON, and it ran just fine.

What's the likely issue?

[cbRider]

It sure sounds like the reserve passages of the petcock are clogged or at least partially clogged.
I would take the petcock off the tank and give it a good cleaning.
To test it you could just disconnect the fuel line from it, turn it to reserve and see what kind of gas flow you have.
On second thought, there could be some settlement in the bottom of the tank. that would give you the same problem.
Let us know what you find.

Karl

[CB750Winger]

  Not sure what model you have but generally the "on" pipe goes up in the tank a few inches but the reserve is way at the bottom of the tank. Chances are it is full of crud. Mine was packed with rust and wasp nest mud from the PO. I cleaned the tank out and coated it. Take the petcock apart and blow it out and clean it good. Clean the tank out as well.       Paul