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Petcock Prime Problems [GS1100E]

witttom

witttom

Forum Mentor
I'm having an odd problem with the petcock on my 1980 GS1100E.

The first of which, is that I'm really not sure how to get it to 'PRIME'. The 80GS1100E uses a petcock different from my 78GS750, or ANY of my other GS parts bikes for that matter. It does not have a traditional knob. There is a small screw-like thing that says prime on it, that can be turned with a flat-blade screw driver, but it does not make any difference in fuel flow no matter how I turn it. When I first got this bike, my first thought was that the knob was broke off. It's not. That's just how it is. But it's odd, and I don't know how it should work.

When I start the bike, fuel will flow as I think it should, but if I turn it off and try to start it again, I get a fuel starvation problem. At that point, it appears to take a greater vacuum to allow fuel to pass than what I think it should. Vacuum line in good shape, no cracks, sealing well. The bike is pulling a vacuum. But after that second start, the petcock acts like it needs MORE pull.

My workaround attempt to get past this, was to swap in a petcock from one of my other donor bikes. Unfortunately, NONE of them fit. I'm stuck with what I have. I've opened this petcock up, and all of the internals appear to be in good shape, diaphragm included. I can take the spring out to ensure fuel flow, but then I'm in a constant-ON position with no way to turn it off. That's potentially bad.

Whattaya think?

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You have the dreaded 1980 petcock with only those two positions, prime and run. It does require vacuum in either position to get the fuel to flow. To test to make sure it's working properly, you can apply a vacuum to it with the carb feed line disconnected. In PRIme, once the vacuum is applied, the fuel will continue to flow. In RUN, application of vacuum will cause fuel to flow, but as soon as vacuum stops, so will the fuel flow. If that is working properly, then you have a problem in another spot, like at the carbs. Good luck!
 
DanTheMan said:
You have the dreaded 1980 petcock with only those two positions, prime and run. It does require vacuum in either position to get the fuel to flow. To test to make sure it's working properly, you can apply a vacuum to it with the carb feed line disconnected. In PRIme, once the vacuum is applied, the fuel will continue to flow. In RUN, application of vacuum will cause fuel to flow, but as soon as vacuum stops, so will the fuel flow. If that is working properly, then you have a problem in another spot, like at the carbs. Good luck!
Click to expand...

Appreciate the input. At least I understand how it works now, or how it should. It's definitely the petcock though. I've pulled it apart a couple more times since I typed up that description. When I put it back together, it works fine when I apply a vacuum (using a syringe to pull air). Fuel will flow. Then I stop with the vacuum, the fuel will stop. Apply the vacuum again, and I get resistance without fuel flow. It would appear that once the valve closes, it doesn't want to open back up again. I just don't know why. When I open the petcock back up, it's not stuck.
 
take the gas cap off and see if you get the same symptoms if you do not have the problem any more then check your breather in the gas cap i'm gonna bet that it's plugged up and just needs cleaning
take the cap out and flip it over take the 2 Phillips screws out and disassemble the whole thing clean it with some carb cleaner lube the lock while your there put it back together and see if you still have the problem
 
Spyderman said:
take the gas cap off and see if you get the same symptoms if you do not have the problem any more then check your breather in the gas cap i'm gonna bet that it's plugged up and just needs cleaning
take the cap out and flip it over take the 2 Phillips screws out and disassemble the whole thing clean it with some carb cleaner lube the lock while your there put it back together and see if you still have the problem
Click to expand...

Same behavior with the fuel cap removed, unfortunately.
 
Apparently, even though the guts of the petcock appear to be good, the diaphragm is sticking in the no flow position. You'll probably have to order a new petcock. Check with Z-1 Enterprises, Jeff Saunders. He's on this forum, one of the vendors. He might be able to hook you up with a new one for a reasonable price. Rebuilding the old one is a waste of time and money usually.
 
I stole the diaphragm from another petcock. That didn't work. Same symptoms. It closes and doesn't want to open back up, offering considerable resistance to vacuum after the initial suck and then stop. It just seems like something blocks the port, so perhaps it's not the diaphragm after all. I then robbed the whole vacuum port panel from the backside of a traditional GS petcock, and swapped it in with the diaphragm from that same petcock (diaphragms appear identical, but the plunger seal is a bit different). I kept the original seal, so that it would seat properly. I am now left with a simplified petcock that ONLY operates via vacuum. No knob, no prime, no on/off, no choices. Simply pulls fuel with a vacuum, and it appears to be working. I'm not particularly thrilled with this setup, but it works and will have to do for now.
 
At least it makes the bike useable. I'd look into a brand new petcock though. I had one that worked fine on the original tank from my '80 GS850L, but I sold the whole works to someone that needed an original 850L tank.
 
On my 79 1000 L(YEAH,L SO STUFF IT) the petcock has a lever that apparently was never meant to move. I got past my starvation issue by disabling the vacuum operation and installing an inline on/off valve.
 
witttom said:
It is a bike that I do not intend to keep. I'm trying to prevent investing anymore time or money into it, if I don't have to. ;) My petcock hybrid hack solution seems to be working well, and have started/stopped the bike several times today without any issues.
Click to expand...

It certainly "sounds" like the OP is PLANNING on screwing over some unsuspecting victim to me here. Hmmm.
I would NOT be trying to help him accomplish this mission myself. Just my $.02
 
GSX1000E said:
It certainly "sounds" like the OP is PLANNING on screwing over some unsuspecting victim to me here. Hmmm.
I would NOT be trying to help him accomplish this mission myself. Just my $.02
Click to expand...

WTF? I'm not trying to screw ANYONE over! What kinda of bullsh!t response is that? How is that screwing someone over? When I sell this bike, I will gladly point out every little flaw to the buyer. I'm simply saying, that I don't want to invest any additional time or money into it. I wanted to take it for a ride. I experienced trouble and didn't understand how this petcock was suppose to work. I asked. I addressed it. My 'fix' has it working better now than it ever has. That's not screwing anyone over.

The paint on this bike is lacking luster and by no means perfect. Am I obligated to paint it too, before I sell it? ...or would that be screwing someone over?
The tires have good tread, but they're probably several years old. Am obligated to buy new tires for the new owner too? ....or would that be screwing someone over?
 
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GSX1000E said:
It certainly "sounds" like the OP is PLANNING on screwing over some unsuspecting victim to me here. Hmmm.
I would NOT be trying to help him accomplish this mission myself. Just my $.02
Click to expand...

That is a rude and uncalled for statement, Eric!
 
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