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Old 04-02-2009   #1 (permalink)
jay67fast is offline Apprentice

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Default Source and fix forG Leak?

OK, I'm BAAAACK, again!
Parked in the garage the other nite, closed the overhead doors and went inside the [COLOR=green! important][COLOR=green! important]house[/color][/color]. (BTW,-- 67, 289, 4bbl autolite 4100 carb).Came back out later into the garage and I smelled [COLOR=green! important][COLOR=green! important]gas[/color][/color]!! Not overpowering, not even strong, but a noticable smell. I checked all the usual places---gas filler cap, sending unit, all the gas line from the tank to the fuel pump, inside the trunk, and from the fuel pump to the carb. No leak, everything is bone dry. The carb itself is bone dry, BUT---I noticed that the manifold to riser gasket was wet. I checked the riser to carb gasket, that seems to be dry also. The manifold itself showed dampness, so I wiped at the dampness with a rag. There wasn't enough dampness to even wet the rag, not enough for me even to smell gas on the rag. However it seems the manifold to carb gasket is definitely weeping. This is strange; I had removed the carb SEVERAL months ago to replace the power valve, and changed that gasket at that a time. I've been [COLOR=green! important][COLOR=green! important]checking[/color][/color]
http://kona.kontera.com/javascript/l...rey_loader.gif
periodically, and haven't had the slightest sign of a leak till the other nite. I wiped the area thoughly, checked the next day, and sure enough, the gasket was damp again. During this time I DID NOT run the engine at all. In fact it's been shut down since Saturday nite.
TWO QUESTONS:
1) It's no problem changing the gasket again, I have spare gaskets, but I got to wondering---- where is the gas coming from in the first place? With the engine not having been run, where is the gas leaking from?
2) would it be OK to use Permatex #2 gasket sealant on both sides of the mantfold to riser gasket to stop the seepage of gas? The gaskets are very [COLOR=green! important][COLOR=green! important]thin[/color][/color], so perhaps some sealant would be called for.
I don't want to mask the problem by sealing the gasket, because I'm not sure what the problem really is, and I don't want to cause other problems.
Can anyone shed some light on this?
Thanks in advance,
Jay67fast
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Old 04-03-2009   #2 (permalink)
The Greek is offline Senior Member

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Did you replace the power valve gasket with one made of nylon? I did and the power valve worked lose. This allowed fuel to drain into the manifold from the now open vacuum side. A ruptured power valve diaphram will cause fuel leakage the same way. It will drain from the fuel bowl and exit the vacuum port located in the underside of the carb's base.

The power valve's vacuum source is located forward of the primary venturies, tucked up inside of the base on the 4100. You probably won't be able to see the source of the leak by looking down into the carb. I replaced that nylon gasket with the usual fiber type, by the way.
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