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carb number 1 leaking with the bike off

  • Thread starter Thread starter gearheadE30
  • Start date Start date
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gearheadE30

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1979 GS750E, with the good old stock VM26ss's. I dipped and rebuilt the carbs when I got it with all new orings, float height set correctly, and jetted for the pods and exhaust. The bike runs fantastically (except for a stutter at small throttle openings, but that's probably better left for a different thread) but after letting the bike sit really much at all, there will be gas on the bottom of the number 1 pod. It's a very slow leak, but I have no idea what could be causing it. My petcock is fine, and all the seals in the carbs are new. The only thing I could think of is that maybe the needle has grit or something on it, but I pulled it apart and everything was fine. Any ideas? What would cause gas to flow out the intake?
 
Leaking float needle valve would be my guess. I suggest measuring the fuel level. The service manual details how. Measuring float height is just an approximation of fuel level. To measure is to know!;)
 
Oh, I guess I forgot to put that in the first post. I thought it was fuel level at first or something along those lines, so I bought the adapter and measured fuel levels and everything checks out. Maybe I should check it again and let it sit a bit with the gauge on and leave the petcock on prime longer and see if anything changes. The strange thing is it's almost more like an evaporation thing. The entire bore of the carb has gas on it, and the only place where it pools is at the entrance to the carb before the venturi.
 
I would also disconnect the fuel line to see if any fuel comes out of it when the bike is not running.

And the vacuum line too may be an unwanted source off fuel to the carbs if the petcock is faulty. ( did you say lo speed stumble??)

Some petcocks do not shut completely off , and may take several hours to show the leakage. both the fuel outlet AND the vacuum line port may leak.

Of course the float valves 'should ' stop the flow into the carbs too but........


that's why we have petcocks!! to make sure the flow is stopped on a stopped engine. After 30 years, the weight of a couple gallons of gas pushes thru bad petcocks then through bad float needles and the result is leaking gas.
 
I did take the fuel line off to make sure that the petcock was actually working and it checked out, but that is very interesting about the vacuum line. I had it off a few months ago (the problem was there then but not quite as bad) and there was no gas nor was there any sign of gas in it.

I really want nothing more than to just put a manual petcock on it, haha. All my other bikes are or have been manual, and I feel like it's just one more variable. That would explain the vacuum-leak-like stutter and varying idle... the carb boot orings are new as well, so that wouldn't be it.

EDIT: just went out and pulled the vacuum line off. It had ever so slight traces of fuel residue on the inside, which could have been from evaporation or turbulence-induced flow from the hour and some long vigorous ride I went on earlier today, but it could also be enough to cause the small leak I'm seeing. For now, I pulled off the line so I can check it over the next few days and see if any fuel comes out of the carb throats or out of the petcock vacuum port.
 
Last edited:
Nessism said:
To measure is to know!;)
Click to expand...
Yeah, there is "some guy" on the forum that has that in his signature. :-\\\

I quote it rather often.
icon_thumbsup.gif


.
 
Nessism said:
Leaking float needle valve would be my guess.
Click to expand...

Me too. I would rule out leaking float needle valve too before plunking down cash for the petcock. Get some clear fuel line and see if the fuel that's trapped in the fuel line after the motor is stopped leaks past the seats. Side stand could explain #1 leaking.
 
btbarb said:
Me too. I would rule out leaking float needle valve too before plunking down cash for the petcock. Get some clear fuel line and see if the fuel that's trapped in the fuel line after the motor is stopped leaks past the seats. Side stand could explain #1 leaking.
Click to expand...


+1 on that!! I entirely missed the #1 thing.... when your needles and/or seats are bad #1 seems to always be the worst when leaned over on the sidestand!!
 
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