fuel petcock / what gives

[graham harron]

I have a 1980 gs 750L I finally got tired of using my mouth to prime the bike as the fuel petcock did not work in the prime postion. So i bought a brand new one and it does the same thing will not flow gas in any postion unless suctiion is applied, any ideas ???? ps its one of thse strange petcocks with no knob just a little slot HELP PLEASE :roll:

[SqDancerLynn1]

Are you turning it to prime or to the reserve position?

[graham harron]

no reserve on this style just on and prime

[Anonymous]

no reserve on this style just on and prime

Wow. That's pretty wierd. Do you think you could post a picture?

Other suggestions: When you suck on it, do you mean that you suck where the vacuum hose is supposed to go? It's a 3/16" hole on the back. Or do you suck on the fuel line (the 3/8" one)?

Michael

[redliner1973]

If there is only one line coming from your petcock, and it is the larger (3/8) fuel line, then you probably have a venting problem. it should just roll right out unless you have the type that has a secondary smaller (3/16) line that hooks to #2 carb. :twisted:

[Anonymous]

Graham -

I recently got a bike with the same petcock - no knob to turn and just prime and on positions. Problem is, when I got the bike, I think the petcock was turned to between positions, and I sort of guessed as to where it was supposed to be turned to. It runs, but I think I might be having some petcock related problems. Could you tell me which way the slit should be turned to for the on position and the prime position? Also, what is the difference between having it in the prime and on positions? Thanks.

--Tyler

[KEITH KRAUSE]

Re: fuel petcock / what gives

I have a 1980 gs 750L I finally got tired of using my mouth to prime the bike as the fuel petcock did not work in the prime postion. So i bought a brand new one and it does the same thing will not flow gas in any postion unless suctiion is applied, any ideas ???? ps its one of thse strange petcocks with no knob just a little slot HELP PLEASE :roll:

If the old petcock and the new petcock do not flow gas in the prime position, then you may have dirt/rust clogging the screen around the petcock tube, or the dirt/rust is clogging inside the petcock valve.
You may also have a clogged gas cap vent.
If there is no clogging and the venting is clear, gas WILL flow in the prime position. HOWEVER, according to the '80 GS1000E/ST shop manual, the engine must be cranked over to initiate flow, EVEN in the prime position.
When the slot is horizontal, it's on. When vertical, it's on prime.
OneStaple, when the petcock is in the on position, the engine vacuum pulls on a diaphragm and fuel flows. When in prime position, the diaphragm is by-passed.
PS: my '79 1000 petcock will flow fuel when in the prime position with no engine cranking. I did'nt know these slotted petcocks required engine cranking to initiate flow in the prime position. So I learned something out of this.

[graham harron]

Thanks everone, Keith i think you hit the nail on the head, I did not Know you needed to crank the motor in prim also i will check this out when its stops raining, !!! THANKS AGAIN

[chuckycheese]

Me too

I also own a 1980 GS750L (which I dearly love) and can almost guarantee you that you will experience more problems in the future...(I hope not!). Those petcocks are awful and I fear a new one won't solve your problems...also, they don't have a reserve which is a major pain. I replaced mine with a Pingle and it's wonderful!!

I wrote a number of posts regarding my petcock change which inlcudes stock numbers and information..It's a really tight fit but a Pingle WILL work and you'll be glad you made the switch!!