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Gas in vac line to petcock......again

  • Thread starter Thread starter randallscott
  • Start date Start date
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randallscott

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hello everyone. i've been working on my 78 750 for a while now, just put it back together after new rings, two helicoils in two spark plug holes, complete teardown+soak+new orings for all four carbs, coil relay, new coils, new plugs, new plug wires, new caps, new points and condensers, stainless brake lines, cleaned calipers(new seals), cleaned master cylinders, fresh brake fluid, oil change, vacuum sync carbs, and....i think that's everything! i started it up and noticed moisture in the petcock vacuum line (i used clear line so i could check for this). sure enough it was gas. thing is, i put a BRAND NEW OEM PETCOCK in a few months ago for this very reason! what are the chances this new part is defective? and just how much gas in this line is necessary to cause problems? could it be something other than the petcock leaking? any help with this isue is greatly appreciated!! thanks, randy.
 
randallscott said:
hello everyone. i've been working on my 78 750 for a while now, just put it back together after new rings, two helicoils in two spark plug holes, complete teardown+soak+new orings for all four carbs, coil relay, new coils, new plugs, new plug wires, new caps, new points and condensers, stainless brake lines, cleaned calipers(new seals), cleaned master cylinders, fresh brake fluid, oil change, vacuum sync carbs, and....i think that's everything! i started it up and noticed moisture in the petcock vacuum line (i used clear line so i could check for this). sure enough it was gas. thing is, i put a BRAND NEW OEM PETCOCK in a few months ago for this very reason! what are the chances this new part is defective? and just how much gas in this line is necessary to cause problems? could it be something other than the petcock leaking? any help with this isue is greatly appreciated!! thanks, randy.
Click to expand...


Only thing that comes to mind would be the diaphram on the petcock is either is not seated properly or has a pinhole leak in it allowing gas to get down that tube. Remember New OEM ( I assuming you go tthis from a dealer and not just a person on ebay saying it was ne ) is likely parts that are old so they are not immune to aging. I would start by inspecting it - guy who helped me with my bike from work used the ol mouth blow and suck to test my petcocks operation... nasty but it did determine my vacum petcock was not sealing entirely I went the pingle route for my switchover.

As that vacum line controls the open and closing of the fuel you ideally do not want it getting junked up with any fuel or worse it not closing properly and then you leak gas into your crankcase...another bad combination

Perform an inspection of it and get back to us.
 
Most likely just gas condensation. The same stuff collects in the tubes of my mercury sync gauge. No reason to panic.
 
Nessism said:
Most likely just gas condensation. The same stuff collects in the tubes of my mercury sync gauge. No reason to panic.
Click to expand...

Yep. Defective parts do happen, but let's not panic just yet. If you look around, most vacuum lines have some sort of condensation in them. A steady flow of droplets would be a problem, but some droplets that sort of just sit there are not a problem.

The best test would be to use a MityVac, apply a bit of vacuum to the vacuum line (not too much), and see if it leaks or pulls gas into the vacuum line.
 
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