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Aftermarket Petcock Issues

  • Thread starter Thread starter Starboard M
  • Start date Start date
S

Starboard M

Guest
Currently trying to clean up what a PO did to my '79 GS750L, and am having issues trying to figure out what to do with my petcock.


It appears to be an aftermarket unit. It will not turn, and seems to be locked onto the run position. I took it off the tank, and it did not have a "diaphragm" like Ive been seeing pictures of on here. Its stamped Japan on it, but no other markings.

When I first got the bike (week ago), its two nipples went to the carbs, and a vent that ran down the side of the bike. After reading on here, I thought that that vent should really go to the 3rd carb vacuum line, but after doing that, and also realizing that there is no diaphragm that most likely did more harm that good.


So, my question is, what kind of petcock do I have, and what should I do about the other nipple as well as what do I do about the carb vacuum line?
037.jpg


041.jpg

Thanks!


edit: The fuel gauge overflow line has been unplugged. Not sure what it was plugged by some PO, other than it might leak a bit?
 
The big one with 4 bolts is your sending unit, the line with the bolt and clamp is a vent. Your petcock looks like it once had a diaphram and the smaller line was the vacuum. If there is no diaphram in there now I would plug off the vacuum port on both the engine side and petcock, and you should have a 5/16ths line running the the fuel rail. I could be wrong.
 
And its been years since Ive worked on a bike with VM carbs but if memory serves me right they dont have vacuum lines only vents.
 
wayfast73 said:
The big one with 4 bolts is your sending unit, the line with the bolt and clamp is a vent.
Click to expand...

It's not a vent, it's a funnel that sits below the sending unit and catches any gas that may leak past the seal. That hose should be open and routed down to the ground in a place safe away from the exhaust and rear wheel in case the sender springs a leak.

And VM carbs do have a vacuum pick up, typically on the #3 carb.
 
Last edited:
I believe you are right, last time I saw those carbs was when I useto work on my dads GS years ago and the number 3 does ring a bell. I cant remember if it was capped or had a line run off it.
 
So I can remove the vacuum line off the petcock and cap the line at the #3 carb?


I read a thread, which Ive now lost, but someone brought up a point that if a petcock does not have a diaphram it will drain fuel into the crankcase (Im assuming its going into the cylinders and past the piston seals?). Is that a legitimate concern, or will it be alright without a diaphram?
 
Without a diaphragm the petcock will never shut off the fuel. This is fine when the bike is running, but when parked the fuel will be continually pressing on the float needles trying to get though. If any of the float needles are a little weak, or if there is some contamination that gets on the needle/seat, the fuel will overflow in that carb, which then will flow into the airbox and engine (crankcase). Bottom line: no diaphragm is bad. You can get a small little shut off valve to put in your fuel line, but it's a pain to use and if you forget, you have the same problem.
 
Hi,

I don't think that petcock is available OEM any more. Z1Enterprises.com might have some kind of replacement if you want to keep the vacuum function. If not, I think you're best bet would be to get a new Pingel unit, with new O-rings and an adapter plate if necessary, and replace the whole assembly. Then cap the vacuum port on the #3 carb. You WILL have to remember to turn off the petcock when you turn off the engine. You don't want to be messing with leaking gasoline. It can mess up you and your bike in so many ways. :eek:


Thank you for your indulgence,

BassCliff
 
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