petcock???

[aronc850]

i own a 79 gs 850 and when the petcock is arrowed toward res it is on full flow. but when the arrow is on res it is shut off.. and when it is on fuel it does not work again. so what are some ideas for this??? Please any help would help

[GSstiny]

If its a stock petcock its vaccum operated. The engine has to be making vaccum (running) in order for it to flow on run or reserve.

If it is running, it may be gunked up, especially if the bike sat with unstabilized fuel for a while. A good cleaning may be all it needs.

[Jethro]

The inlet for reserve is much lower than the main inlet. It is easier for the reserve inlet to get clogged. That could be part of it, but as GSstiny said, the fuel tap requires vaccum from the engine to function. Does the tap have a "prime" function? That should work without vaccum, and pulls from the same inlet port as reserve, so check that. If flow still isn't available, you need to clean and rebuild the petcock.

[Doctor Shifty]

i own a 79 gs 850 and when the petcock is arrowed toward res it is on full flow. but when the arrow is on res it is shut off.. and when it is on fuel it does not work again. so what are some ideas for this??? Please any help would help

Hi,

I suspect that the first time you mention "res" here you mean "pri" for prime.

The petcock has three settings, two (run and reserve) are closed until there is vacuum on the control tube, the third (prime) runs without vacuum.

You can test the operation by taking the small tube off the 2nd carby and gently sucking on it. This will open the petcock on run and res settings. Don't suck very hard, you only need enough to give a bit of resistance.

It works like this so you don't have to turn it on and off. But when you need to fill the carbies you can prime them.

Hope this helps.
Kim

[BRycraft]

Replace Petcock

I would strongly recommend replacing the petcock with a non vacuum operated type. I had a problem with mine that gas was pouring into the vent line flooding the carb and gas was dripping out the exhaust. I purchased for about $12 a Pingle adapter plate and for $16 a new petcock that has 3 positions Run Off Reserve, the only problem is you have to turn it off after you shut down the bike or it could flood the carbs if the floats are not seated perfectly. All I had to do was grind away a small area for the round petcock to fit thru the tank. The kit includes an adhesive that you apply to a gasket and the adapter plate, you secure the plate with screws that match the holes already in the tank, then wrap the petcock with some teflon tape and screw it in the adapter plate. My particular hole separation was 44mm something you need to know before ordering, there are not many configurations so it isn't that hard finding the exact size. The petcock has a 3/8 inch NPT (National Pipe Thread) threads on it and all you do is screw it into the adapter plate, hook up the fuel hole and put a plug on the vent on the carbs. Those vacuum operated petcocks are nothing but a constant problem. What is nice with this adapter plate I can replace the petcock with any 3/8 inch npt threaded petcock and they are available everywhere. Do yourself a favor and get rid of the vacuum petcock. The only reason they made them was so the owner didn't have to remember to shut off the petcock when he was done riding, but those diaphrams fail after a while and you could be in the middle of riding when it could do what it did to me and that was flood the carbs, fortunately I was in my garage and not on the street when it happened, gas in a hot exhaust is not a good thing.
Good Luck. Bill

[2ndstage]

Where did you order thse from Bill?
Do you have any part numbers?

Thanks

[bigbill]

I second BRycraft's suggestion, get a Pingle. Mine bolted up with no mods. I got a dual outlet setup for my flat slide carbs. No problems since, starts and runs great. Go to Pingle web site and get part numbers. I ordered it then from Dennis Kirk. goodluck