Carbs leaking gas over night.

[Garrett411]

Hey Guys. For the last few days after i've rode short trips the next morning when i go to start my bike i've found a film of fuel beneath the carbs on my '79 XS-F. Now i am not sure where the leak is coming form but it looks like there could be some coming from the back of the float bowl. But after some time i tried switching the petcocks to reserve and placed a clean rage under the carbs for a night. The next morning there wasn't any fuel that i could tell on the rag or the bottom of the carbs. This leads me to think that the petcocks are allowing fuel to drain in to the carbs overnight? What do you guys think? Faulty petcocks/gasket?

I just removed the carbs because i have some tuning to do. I cleaned them this winter and the the needle and seat and all gaskets looked fine. I ordered a new float bowl gasket anyway to try and cover all the bases. The carbs are Bs38's btw.

Thanks guys
Garrett

 

[XSLeo]

79, Does that have vacuum pet cocks? If so they probaly need rebuilding.
In the on position, no fuel should flow without the engine running.
You have the carbs off, run the fuel lines into a small jar. Let it set over night, does any fuel collect in the jar. If you have two petcocks run the fuel line from each petcock into seperate jars. This will id which petcock is leaking.
The petcocks are shut offs, the float valves are not shut offs they are metering devices.
Leo

 

[Garrett411]

Thanks for the fast reply!

Yes it does have 2 vacuum petcocks. With fuel lines off and the petcocks on i can watch fuel drip out about 10 drops per minute. I had suspicions about this because before the tank was painted and the petcocks weren't removed there was no leak. Should i order a rebuild kit or just disassemble and clean?

 

[650mark]

fwiw, those petcocks are notorious for leaking and being very prone to problems, even after rebuilding them. I'd opt for replacing them with non vacuum ones and be done with it. btw, 1 new petcock will easily flow enough fuel to warrant eliminating the other one, just make a good block-off plate for that side. btdt 4 times with excellent results.
I bought the non vacuum petcocks from mikesxs and so far have had very good success with them all. yeah, some of mikes stuff is junk but his petcocks work well.

 

[Garrett411]

I was thinking of going with that route. What is the part # for the non-vacuum ones? As for the plat did you weld it or just silicone the edges and screw it on with existing bolt threads?

 

[650mark]

mikesxs part # 20-0019 for the petcock. also a good idea to get some new mounting screw washers #20-0018. as for blocking off one of the petcock holes I just cut and shape an aluminum plate and either seal it with a very good quality fuel resistant sealer or use a regular petcock tank-to-tap o-ring. don't plug up the original holes with sealer, you may want to install another petcock there someday. have at it...

 

[Garrett411]

Awesome. Thanks guys!