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Fuel Cock Testing

Posted: Tue Jul 19, 2011 10:21 am
by oldjapanesebikes
I got fed up with trying to get the fuel cock working properly on my GT500, so I made up a test rig out of a large coffee can which made it much easier to trouble shoot and test. I used a spacer block from a GT750 on the inside of the coffee can so I could get a good gasketed seal on both sides of the tin and rather than gasoline/petrol I used mineral spirit (varsol/paraffin) - its just a lot safer. You can get an auto-ignition due to static electric build up from gasoline flowing through fuel lines into a catch container (obviously when testing you don't want it all over the floor) which could put a serious cramp in your day. :wth: I suppose you could use water, but then you'd have to get the valve dry before commissioning.

After a bit of Rick's trick with the bamboo chop stick end to burnish the valve seat, the addition of a viton o-ring seal on the pintle, slight adjusting of the spring tension and new gaskets and seals, all is now good ! 8)

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Re: Fuel Cock Testing

Posted: Tue Jul 19, 2011 1:23 pm
by rbond
Dis you replace the diaphragm too? Mine is from another bike the P.O. used. It is working OK, but Iam looking to the future when it will be necessary for a re-build.

Re: Fuel Cock Testing

Posted: Tue Jul 19, 2011 2:39 pm
by Coyote
I did the very same thing years ago when rebuilding a GS1000 petcock. I use a model airplane fuel bulb to pull a vacuum, but lung power also works. I used plain old isopropyl (rubbing) alcohol for the test fluid. It's thinner than water and can be followed with gasoline immediately.
For those who don't know, a GS1000 (78 -79) petcock will work on a GT tank. The bolt pattern is the same. Single vacuum and single outlet.

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Re: Fuel Cock Testing

Posted: Wed Jul 20, 2011 12:19 pm
by oldjapanesebikes
rbond wrote:Dis you replace the diaphragm too? Mine is from another bike the P.O. used. It is working OK, but Iam looking to the future when it will be necessary for a re-build.
No - I was lucky enough to be able to use the old diaphragm. I do Like Coyote's idea though - full rebuild kits for those, complete with diaphragms (!!!) are easy to locate. :up: