Need help with 1977 Suzuki GS550 fuel lever settings?

Question

I have three setting on my GS550 fuel tank. Counter clockwise from left to right they are RES, ON, and PRE (maybe PRI, not sure). I know that RES is supposed to be reserve, and ON is obvious, but what is PRE? I took the tank off with the setting on PRE because I thought leaving it on ON or RES would let gas leak out. Just the opposite happened. Gas leaks out of the bottom fuel line on PRE, but nothing comes out of either the top or bottom line when the lever is on ON or RES. Is this right?? the bike runs like it's starved for gas--needs starting fluid to get going, doesn't idle, etc. Any help with this would be greatly appreciated.

Answer 1

Since you already have the tank off, you're in for an easy fix.

The PRI position is Prime - open all the time. The petcock is vacuum operated. When the engine is turning over, vacuum from the carb goes to a diaphragm in the valve and opens it. You will not have flow without vacuum in the other two positions.

Since the gas only leaks out in the prime position, it's a good guess the petcock or it's screen is clogged. Remove the petcock from the tank and flush it out.

If the petcock and it's screen are clear, the idle problem will be in the carb.