Petcock question

[mopar19]

hey all. I think I'm having petcock issues. First, I rebuilt the petcock with an overhaul kit. But after putting it all together and putting fuel in the tank, I'm not getting any fuel from the petcock to the carbs. I pulled the gas line and sure enough no fuel is coming from the petcock in any of the positions (res, on or prime). My question is, should fuel be coming from the petcock at all with the bike not running? I know this has a vacuum diaphragm (think that's how you spell it). If it's possible, can someone tell me the sequence of installing the overhaul kit? I took it apart and didn't get back to it until a week later and I don't recall if the spring on the diaphragm side goes against the diaphragm with the small rubber O ring or on the side where the cover goes on. Thanks for any help!

[tkent02]

What year bike? There are slight differences.
Fuel shouldn't flow unless the bike is running except in the prime position.
New style petcocks, seems like it needs a little vacuum to start the flow even in prime, can't remember for sure.

[mopar19]

Sorry guys, its a 81 gs850GL.

[mopar19]

Also want to note, I did spray starting fluid in the carbs to try and get some vacuum, the bike started for a couple of seconds, but I don't think it helped.

[tkent02]

Test it out.

Disconnect the two hoses from the petcock, and connect longer hoses to it. Leave the carb ends attached to the carbs, they are sometimes hard to reinstall.
If the tank is fairly full, turn the petcock on. If the fuel is low in the tank, put the petcock on reserve if you have a reserve position.

Suck on the little hose, fuel should flow from the big hose.

In prime position it should keep flowing.

In the normal or reserve position fuel should stop flowing when you stop sucking.

[Dogma]

In my fuel flow adventures last year, I noticed that my petcock (80 GS850 GL) would not prime in any position. Since I needed to hold vacuum on the petcock, I disconnected the vacuum line from the #2 carb, opened the drain plug on #1, and sucked on the vacuum line until fuel dribbled out of #1. This took about 30 seconds. I reinstalled the drain plug on #1 and sucked another 30 seconds. The carbs had been dry before, but after this, the bike started and ran as if nothing had been wrong. The alternative was to crank and crank and crank... which killed the battery and didn't always work. On the side of the road.

[mopar19]

Found out the problem. I looked at the old diapragm and saw that it was different than the new one that came with the overhaul kit. The metal cup or circle on the new diaphragm is much bigger than the old one. That was preventing the diaphragm from opening and closing. I put the old one in and the petcock works fine now. No fuel on res or open, but fuel does come out in prime now, like its supposed to. Thanks for everyones responses.

[jimcor]

Most times it's worth the extra money to buy an original Genuine Zook part when it comes to those damn petcocks. I hate 'em. Gimme a good old manual petcock anyday. Switching on and off just becomes part of the ritual.

[1980GS1000E]

I had exactly the same issue with a diaphragm I bought off ebay for $13. After trying to reshape the little bugger, I threw it in the trash and sprung for a new petcock assy. I think it was about $50.

[robertob]

I had the same problem. The aftermarket diaphragms are worthless. I got mine from Z1 enterprises and they won't give my money back even though it's a defective/poor fitting product.

[Steve]

I am glad you found the problem and got it fixed, but this line from a previous post sort of scares me:

Also want to note, I did spray starting fluid in the carbs to try and get some vacuum,

Starting fluid is wonderful when necessary and when used properly, but those two items seldom happen. It is just too easy to spray too much fluid trying to get it to run, and the results are occasionally considerably less than pretty.

I am also trying to figure out ... how does spraying starting fluid create vacuum?


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