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petcock?

  • Thread starter Thread starter 03svrider
  • Start date Start date
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03svrider

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i bought a pretty clean gs450 tank off ebay considering the stock tank has alot more rust in it. the bike runs fine with an inline filter but why let a clean tank sit on the bench? in testing it for leaks i have put it on the bench with some fuel in it and with the petcock turned to "pri" the fuel just pours out! on "res" or "on" it just trickles. what gives? i thought the "pri" setting was off considering the two other options of "res" and "on". am i missing some elemental/basic fact considering the tank is not hooked up at all? if the petcock is bad i can just switch it with the one on the bike now that operates fine. thanks for any input.
 
Something I can answer!

Something I can answer!

Oooh! Ooooh! I know the answer!

The three settings of my 79 GS250 are:

ON: Normal operation position: Theoretically, it is controlled by engine vacuum and releases gas while engine is in operation, while blocking flow if the engine is stopped. Dried seals or something else might cause it to release fuel without "seeing" the engine vacuum.

RES: Same as "ON" except from a lower tap point in the tank.

PRI: "Prime." This _should_ release a full stream of fuel, to fill the carb if the fuel system needs to be primed.

The trick for me is remembering which position is which while riding after the motor's started stuttering at night....

Mark
 
mf70 said:
Oooh! Ooooh! I know the answer!

The trick for me is remembering which position is which while riding after the motor's started stuttering at night....
Click to expand...

The answer to that is quite easy, Mr. Horshack. 8-[ (Does anyone else remember Welcome Back Kotter? )


Presuming it's the same on all GS petcocks, the petcock lever pointing down will give fuel when the engine is running. When it runs out, if you want to keep going forward, turn the petcock to point forward. 8-[


03svrider,
I would be more concerned about the trickle that comes out in the ON and RES positions than the free-flow in PRI. As mentioned, the free-flow in PRI is normal. If you have not ridden the bike for a while (shame on you :oops: ), it will start easier if you move the lever to PRI for a minute or less, then start it after the carb bowls are filled. Don't forget to move it back to ON before riding. Nothing bad will happen, but I believe the PRI position bypasses the reserve function on the petcock, so when you run out, you're OUT. :shock:

Take the vacuum side of the petcock apart carefully to see why the trickle is there. It might just be an o-ring that is not seating correctly. Fix that and you are good to go.


.
 
Steve you are on the right track for the valve.
Be careful, loosen the 4 screws on the back of the valve, but don't remove them. The back is under pressure from a spring, but more than likely the 2 halves are stuck a bit to the diaphragm. To separate, hold in the hand and give the valve a rap with the hilt of a screwdriver. When the halves spring apart, you can remove the screws.

More than likely the back half will pop loose with the spring, be careful and remove the diaphragm, it shouldn't be stuck too bad if at all.

On the opposite side of the diaphragm from the spring is a post with an O ring. Short of a hole in the diaphragm, that O ring is your valves seal. The O ring seats against a cone shaped seat.

If that seat has any corrosion, you can change the O ring, it might stop it for a while, but it will eventually leak. And here I think is the problem with rebuild kits. There is nothing wrong with the kits, it's the part they are meant to seal against.

I have cured this problem. I took an aluminum stud that is used in holding packs onto frames. The head of the stud was just the right diameter and thickness to produce a honing cone on the end. I took a file and tapered the edge while running it in a drill. I dipped that end in chrome polish, inserted the end into the valves seat and turned it on, after a few seconds, I stopped, cleaned the seat with gas and small brush and checked the results. I adjusted my home made arbor a couple times with a file, before I got it wright.

I polished the seat until no pitting was observed. Now you can have confidence that the O ring will do it's job. Even if you got the angle of the arbor a little off, the O ring should seat.

Put everything back together, clean the bottom mounting surface of the valve and tank, and gasket.

Remember there are washer seals under the heads of valve mounting bolts.
V
 
I forgot to mention that you have to activate the diaphragm with vacuum on the ON and Res positions if the valve is functioning properly.
 
thanks guys. we'l see what's what when i start wrenching on the petcock
 
03svrider said:
thanks guys. we'l see what's what when i start wrenching on the petcock
Click to expand...
Personally, I think you should leave 'wrenching at your petcock' to something done in the privacy of your own home.

I try and leave my pet cock in my pants at all times when I am out in public. Particularly in the winter time. :D
 
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