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1979 GS750E petcock won't shut off completely

Runningdog

Runningdog

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The petcock will not completely shut off when on run, with no vacuum to it. I replaced the gaskets and diaphragm with an aftermarket kit. Fuel slowly leaks from fuel spigot. I installed gaskets and seals from Suzuki, except for the diaphragm......still leaks. I put a fine layer of silicon grease on the diaphragm mounting plate, both sides....still leaks. The Suzuki diaphragm is no longer available. Pingel? Half my other bikes have manual off positions on their petcocks, so this is already a habit to shut off at the end of a ride.
 
Did you inspect & clean the seat that the "O" ring sits against good? I found a pencil with a eraser that fit proper down in there to kind'f buff or polish it good.. Did it on my "05" Bandit a few yrs back as crankcase was full of gas after winter nap. Not wanting to wait on parts, just cleaned good, stretched the spring a bit, & put it back together. It's still working fine.
 
Good idea....looks clean, but I don't have micrscopic vision. That's next step.

Whup, an hour or so later, tried the pencil eraser orifice editting, and stretched the spring, but did not solve.......made so much sense to me, too.
 
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The forums' wisdom is that the the rebuild kits don't really work. Don't know how much of it is truth, but when I had to replace mine, the shop I sometimes go to had an NOS GSX petcock in the parts bin and I used that one instead. For an upcoming rebuild I got apparently newly produced ones (looked waaaay to clean for 40yrs NOS) for a decent price.
 
Glad I didn't guarantee anything, sorry it didn't help... Luck with what you do next.
 
I gleaned additional wisdom from the forum, and ordered an ebay one....should have it at my door in a couple of days, for $32CAD...cheap to try out.
 
Received the new repro petcock a couple of days ago.......looks OK. Did not include the mounting bolt gaskets, as I expected, so now I wait for ten days for Suzuki gaskets to arrive from Toronto. No worries, still waiting for cam cover gasket.
 
Aw shuicks!! about like buying an oil filter then get home and find it doesn't come with a "O" ring... Just don't make sense.
 
Thas right. Huh, I had to add more digits so I could post Thas right.
 
Brake lube will swell real rubber O-ring gaskets a bit, don't leave it in a container for more than a few minutes, they can really swell up quick, then dry it off, if the O-ring seems thin. Swell as necessary. I would suggest putting an in line shut off valve. A leaky fuel switch can cause gas to build up in your crankcase, (depending on how the carbs are) and you end up with a crankcase full of gas and oil. Seeing as you have this problem already, I would suggest doing an oil change, it probably has gas in the crankcase.

I left my Suzuki on prime by accident, and by the time I got to work (45 miles away) I noticed the temperature rising. I looked and realized I had left the fuel selector switch in "PRI". I was lucky the guy at the corner gas station let me do an oil change right there, supplying me with a pan to collect the oil, and a propane torch to swell the copper ring back up. I didn't worry about the Oil Filter, and had no problem with the bike afterwards. The Oil Level gauge was so high, way past the highest level indicator. That's one way of telling there is gas in there. ;)
 
Tank with new petcock installed is sitting on the bench, has not yet been on the bike. Fuel outlet has not leaked, so that part of the issue seems solved. Still weeps around mounting bolts, so will address that when new mounring gaskets get to me.

Bike is almost ready to insure (has been approved for Collector Plate), little parts still to arrive, and winter sand to get swept. Bike has only been run for about half an hour since a top-end rebuild, so is almost due for the breakin oil change. I'll schedule that after I have a look at oil/fuel potential in the crank case.
 
Received the mounting bolt gaskets today, petcock does not leak anywhere, now, so that is a good thing to report.

Mounted tank back onto the bike, but, you know, those repro petcocks just do not fit on a 1979 GS750E. Outlet and vacuum ports are pointing in the wrong directions, mainly toward unreachable parts of the frame under the tank. I could use longer vacuum hose, and quick-connects for the fuel line, but still not a very elegant installation.

Pingel?
 
OK, more progress on the fuel cock saga. I compared internal parts on the OEM tap (with the new aftermarket kit) with the ebay tap. I noted that the o-ring projection on the aftermarket kit diaphram was not as long as the ebay diaphram. Swapped those parts, and it fit into the OEM tap, and therefore I was able to put the OEM tap on the tank and on the bike, with the proper hose access. Left this setup on the tank, with fuel in the tank, for a couple of days, with no leakage. Turning the tap handle from prime to on to reserve showed the correct fuel feed. Put the tank back on the bike, ran the bike, and left the whole thing sit for a few days.....no leakage from the tap.........wahoo, looks like I've cleared that miniscule, frustrating hurdle.
Never did find a new OEM tap to try.
 
I'd hardly call a leaking tap (that has no off switch) a miniscule problem. Especially since Suzi resides in my living room. And has not been emptied of gas. Or oil. Brake fluid...fork oil...

Unburned hydrocarbons morning, noon and night. Yummy! :anonymous:
 
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