GS750 Petcock test

[ybot1966]

I dismantled and rebuild petcock putting in a new diaphram and seals etc

when put back peterol run from the fuel line at all setting, vacuum line was not connected to a line, just petrol in the tank with the petcock on

I found a test below of the petcock as im not sure if the vacuum valve is faulty

(Last year I replaced my Eiger petcock because the fuel was not shutting off when the bike was turned off. (I discovered this by accident when I pulled the fuel line off of the carb to change jets). However, this year it is happening all over again. So this time, I pulled it off and took it all apart to see if there was any dirt in it. The petcock was clean. As a test of its' operation, I blew through the fuel outlet and air flowed through with the dial in all positions. (is this normal?). I then held my finger over the vacuum inlet and could not blow any air through unless the dial was in "Prime". This operation made sense to me.)

Can anyone confirm this test would ensue the valve is working ok, as i dont think the vacuum line needs to be connected to stop fuel flowing in the on or reserve settings/

Thanks Toby

[earlfor]

I dismantled and rebuild petcock putting in a new diaphram and seals etc

when put back peterol run from the fuel line at all setting, vacuum line was not connected to a line, just petrol in the tank with the petcock on

I found a test below of the petcock as im not sure if the vacuum valve is faulty

(Last year I replaced my Eiger petcock because the fuel was not shutting off when the bike was turned off. (I discovered this by accident when I pulled the fuel line off of the carb to change jets). However, this year it is happening all over again. So this time, I pulled it off and took it all apart to see if there was any dirt in it. The petcock was clean. As a test of its' operation, I blew through the fuel outlet and air flowed through with the dial in all positions. (is this normal?). I then held my finger over the vacuum inlet and could not blow any air through unless the dial was in "Prime". This operation made sense to me.)

Can anyone confirm this test would ensue the valve is working ok, as i dont think the vacuum line needs to be connected to stop fuel flowing in the on or reserve settings/

Thanks Toby

In the ON or RES position, fuel should only flow if there is a vacuum applied to the vacuum line. With the vacuum line disconnected, there should be no fuel flow in ON and RES.

Prime should allow fuel to flow always.

I doubt blowing into the fuel outlet on the petcock would be a valid test since that is opposite of the normal direction of fuel flow.

Earl

[ChicagoBob]

Sounds like you may have installed the diaphram with the spring on the wrong side, or in some other way disabled, or there is something blocking the action of the diaphram. Could also be an o-ring issue.

I would review Bikecliff's petcock rebuild page, at http://members.dslextreme.com/users/...ck_rebuild.pdf, and try again.

[ybot1966]

Thanks Bob
i followed cliffs guide which is great, it seems to be ok now but will change the settings a few time before putting the tank on, when you mention the O ring there is a rubber ring around the diaphram head is this it or should there be another one?

Toby

[ChicagoBob]

I meant the small ring around the diaphram post. It's what shuts off the fuel when the engine is off and no vacuum is present.

[ybot1966]

yeah that was on the new diaphram thanks

Toby

[Guest]

Sounds like you may have installed the diaphram with the spring on the wrong side...

I did that once & that's exactly what happened - cancelled out the vacuum shut off.