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Petcock on '79 750

  • Thread starter Thread starter Anonymous
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Anonymous

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I have a 1979 gs 750e that isn't getting enough gas at idle. If I put it on prime then it runs fine. I haven't checked the vacuum line yet and I do suspect this to be the culprit, but incase it isn't the vacuum line is there a way to check the vacuum or petcock? I know the petcock doesn't leak and it gets enough gas when set to prime so I don't think the petcock is the problem. However, if it is bad can I just run it on prime and turn it off every time? I?ve noticed that a lot of people recommend pingel petcocks; won?t that be the same as running it on prime? If I do get one that isn't vacuum operated should I just plug the vacuum line? I have the vacuum line coming out of carb #3 (from the left) I also have k&n pod filters, a 4 into 1, and rejetted the carbs to match.
 
Your petcock is probably gumed up inside and is not opening up all of the way, or the petcock diaphram is leaking,and not allowing it to open fully and is in need of rebuild. Pingle MUST be turned off, when the engine is turned off
 
i checked the vacuum line and it is fine, no cracks or anything. is it possible that the engine just doesn't create enough vacuum?
when the pingel petcocks are on, is that the same as turning my current one to prime? if so can't i just run with it on prime and turn it off after i'm done riding?
 
NO, it isnt possible the engine does not create enough vacuum. It takes much more vacuum to pick up fuel through the jets and spray a mixture than it does to activate the diaphram in the petcock.

A Pingel petcock is a mechanical off/on petcock. There is no vacuum connection to it. A Pingel in the on position is the same as your stock petcock in the prime position. No vacuum is required for fuel to flow. You probably should disconnect the vacuum tube to your stock petcock and plug it. On my 79 750 with a Pingel, the vacuum line off the carb is only two inches long and has a screw in the end to cap it off. Without a vacuum line on your stock petcock, the run position will be an off position since there is no activation by vacuum of the petcock. Reserve will not be enabled. The difference is that a Pingel is a mechanical positive off and you petcock is an off only by lack of diaphram activation. A Pingle cannot
malfunction and allow fuel to flow when off, but the stock petcock could.
You will have to always remember to switch from prime to off (which was run) because you will get fuel in your crankcase oil if you forget.
(if you do forget, just change the oil, dont even wonder if any fuel got past..............it DID!)

I guess the short answer to your question is............YES. :-)

Earl




MattD said:
i checked the vacuum line and it is fine, no cracks or anything. is it possible that the engine just doesn't create enough vacuum?
when the pingel petcocks are on, is that the same as turning my current one to prime? if so can't i just run with it on prime and turn it off after i'm done riding?
Click to expand...
 
The vacuum line must come from the #2 carb from the left, that is, the inside left carb. If you have it coming from the inside right carb (#3 from the left) you have it connected to the overflow line which doesn't have any vacuum.

Harrison
 
I really think that it is supposed to be the third carb for the vacuum line. i've put my finger over the end of the tube and felt it sucking on it. I will try the number 2 carb but i don't think it will work.
 
Nope it is the number two carb.......Get yourself a pingle petcock and you will be happy
 
If its mechanical slide carbs its the #3 carb with vacuum
Thats starting from the left side of the bike when sitting on it
 
I'm sitting here with the carb set in my lap and it really DOES come off the #3 carb, so I was wrong and I apologize. You would think that as many times as I've taken these things off the bike I'd have noticed. It just LOOKS like it's off the #2 carb. Geez, I hope my kids don't pass on the stupid genes.

Harrison
 
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