Page 1 of 2

Furtive fuel leak

Posted: Sun Apr 14, 2024 12:21 pm
by Alan Pershing
I've been chasing this for two weekends and thought I'd reach out to the group for suggestions.

I have a fuel leak ONLY when the car is running and ONLY on the driver's side of the engine. The car will run for a few minutes seemingly fine and then I'll start seeing small droplets (I put down paper towels to see the pattern). It drips down the pushrod tubes and right on top of the flapper box. I removed the flapper box and ran the test again with a paper towel under to car and there is a series of drops under the pushrods. It's not a gush, just a slow water torture kind of dripping.

In one of the pictures you can see a drop getting ready to fall and some dampness above it. The two lower pictures are sideways.
IMG_3020.jpg
IMG_3023.jpg
IMG_3024.jpg

I've replaced the gaskets on the carburetor and the intake manifold, changed out all the washers to the ones spec'd and even torqued all the nuts and bolts to no more than 15 lbs (per Al Zim) and it is still leaking. I don't feel any dampness on any fuel lines and nothing around the carburetor or the intake manifold. I have the engine tin removed and the edges of the gaskets look dry to me (I checked with a boroscope as much as I could).

So I'm definitely at a loss. If anyone can point me towards possibilities I'd appreciate it. I have a lift so getting access to everything is pretty straightforward. And I'm getting sadly proficient at removing the carburetor and intake manifold and reinstalling them (over and over and over).

Many thanks!

Re: Furtive fuel leak

Posted: Sun Apr 14, 2024 12:34 pm
by Mike Wilson
Alan: what type of carbs? If Zeniths, I would suspect a faulty float needle valve, a bad float or a leaky soft plug on the body of the carb. If Solex, I'd suspect a sinking float. Others more knowledgeable will certainly weigh in.

Mike

Re: Furtive fuel leak

Posted: Sun Apr 14, 2024 12:44 pm
by Alan Pershing
Weber IDFs 40s.

Re: Furtive fuel leak

Posted: Sun Apr 14, 2024 12:55 pm
by Mike Wilson
Maybe an incorrect float level or maybe the fuel line attachment point on the carb? Did this just start or has it been a problem?

Mike

Re: Furtive fuel leak

Posted: Sun Apr 14, 2024 2:17 pm
by David Jones
Place the paper towel under the fuel line and move it along until you see the leak. From where you are seeing the leak I would suspect the "T" between the shroud and left carb.

Re: Furtive fuel leak

Posted: Sun Apr 14, 2024 2:41 pm
by Jim Clement
fuel pump / fuel pump gaskets ?

Re: Furtive fuel leak

Posted: Sun Apr 14, 2024 3:04 pm
by Alan Pershing
No, they all appear to be fine. I found a carb rebuild kit that I had unused so I'm going to replace the washers in the float mechanism and recheck the float level, then see what happens. The needle valve seems to be working fine, the ball bearing moves up and down easily with no issues.

Re: Furtive fuel leak

Posted: Sun Apr 14, 2024 4:00 pm
by Alan Pershing
Ok, replaced various gaskets on the float mechanism and reset it to the correct height but no difference, still leaking.

I took dry paper towels while it was running (and leaking) and ran them all around the carb body, the intake manifold body and all the way down to the spark plugs. No dampness anywhere.

Here's a picture of the pattern of drips (pictures keep loading sideways, sorry):
IMG_3025.jpg
Then while the car was running (and dripping) I lifted it up and got underneath it. All the drips seem to be originating at the last long fin where I have the long screwdriver pointed and then rolling off the tubes and onto the paper towel:
IMG_3027.jpg

Re: Furtive fuel leak

Posted: Sun Apr 14, 2024 5:03 pm
by David Jones
Swap carbs side to side, no need to hook up throttle linkage as it will run on idle, then see if leak persists on same side or moves with carb.

Re: Furtive fuel leak

Posted: Sun Apr 14, 2024 9:50 pm
by Alan Pershing
Great idea, I'll try that tomorrow after work.

Re: Furtive fuel leak

Posted: Mon Apr 15, 2024 10:50 am
by Doug McDonnell
Out of sight - out of mind. Check the short piece of fuel line behind the fan housing.

Re: Furtive fuel leak

Posted: Mon Apr 15, 2024 10:59 am
by Alan Pershing
Nope, the lines are all in good shape and dry as a bone. I had a thought last night and I'm going to swap the floats between the carbs today to see if the leak moves to the other side. If it does, the float is the culprit; if not, it could be the carb body.

Re: Furtive fuel leak

Posted: Mon Apr 15, 2024 1:46 pm
by Martin Benade
If it’s running reasonably well while dripping I’d guess that the float is functioning. If it’s not you’d be getting terrible running, stalling, and hydrolock. I’d go right to swapping the carbs.

Re: Furtive fuel leak

Posted: Mon Apr 15, 2024 2:15 pm
by Alan Pershing
Swapped the floats at lunch and the leak stayed on the driver's side. There was more gas in the float bowl on the side that's leaking so before I did the test, I evened that out and double-checked the float levels side by side to make sure they were the same (they appeared to be). I don't know enough about carbs to know why one side would have more gas in the bowl; it wasn't crazy different but it was different.

I'll take the driver's side carb body off after work and see if anything jumps out at me as obviously out of whack.

Re: Furtive fuel leak

Posted: Mon Apr 15, 2024 2:34 pm
by Wes Bender
I'm with David and Martin. Swap the carbs. Problems are solved more quickly when you can cut the possibilities in half.