Petcock or floats ? Need advice!!

[RickLee]

I bought an aftermarket petcock for my 1981 GS 1000 that is supposed to vacuum feed fuel when the bike is running, and shut off the flow when the bike stops running. Well it seems that when the bike is off, it keeps flowing anyway.  I took off the tank and tried the three positions on the petcock... there is no off... it flows in all three positions.  I’m aware that the on position is supposed to be on only when the bike is running and producing vacuum, and off when not producing vacuum. The prime and reserve are not supposed to be off positions.

the problem is that the carbs filled up and emptied gas into my air box... lots of it.  Should the floats have stopped this from happening or is the pressure from the flowing fuel pushing its way through ?  I’ve ordered another petcock but in the meantime is there a way I can make this faulty one work in only an on and off position?   I read a thread where someone put a piece of rubber where the diaphragm goes and got it to somehow do an off and on position.   Any details on this Temporary “fix” would also be appreciated.     Thanks All!

Edited October 2, 2020 by RickLee
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[Gixer1460]

The reserve should also be vacuum controlled. The prime position just lifts the diaphragm to admit fuel to 'prime / fill empty float bowls.

And yes your floats and their associated float valves should not allow fuel to flow once the bowls are full - so they need a service as well!

I can't see how trying to control a leaky diaphragm is going to help - even if you 'turn it off' it'll still leak which the carbs can't stop either!

[RickLee]

Not the answer I was hoping for obviously but you are most likely correct.  I was hoping I would not have to go into the carbs but it’s an old bike and I have all winter. Thanks gsxr

Edited October 2, 2020 by RickLee

[RickLee]

The bike has been sitting quite a long time.  Until I get a little more money to put into it, could I drop the bowls and clean and make sure the floats are not stuck?    
 

 This morning I took the diaphragm out of the old petcock and slid it into the aftermarket petcock. It fit very well and the rubber is much thicker. Seems to be working fine now.   The reason I’m not using the old original petcock is because the filter had been broken off for some reason. The old original petcock is full of sludge.  Can these petcock filters be removed and replaced if I decide to rebuild the old one!   

Edited October 2, 2020 by RickLee

[Gixer1460]

The original tap filters are designed to keep rust flakes getting to the carbs but not much else as you've found in the tap and i'd suspect in the carbs as well ! Most on here will use an inline filter for insurance but a session cleaning out the tank wouldn't hurt - and costs nothing. likewise taking carb float bowls off and cleaning them out. May not be a proper clean but all of the float valves should hold air pressure if you blow through the feed pipe!

[RickLee]

Thanks, I spent 3 weeks off and on cleaning the tank. I’m confident it will be good without a sealer.  The bike has an in-line Fuel filter on it.... looks clean.  Funny thing is it was running fairly well and didn’t start leaking gas out of the carbs until I shut down the motor. Then all hell broke loose. I was thinking about fire lol.   I will give the carbs a good cleaning.

[BigT]

Follow this guide for your carbs

http://zeus.mtsac.edu/~cliff/storage/gs/Mikuni_BS-CV_Carburetor_Rebuild_Tutorial.pdf

There's an O ring under the float valve seat that fails and fills the carbs

 

I see you're just up the road from me

 

Edited October 9, 2020 by BigT