Furtive fuel leak

356 Porsche-related discussions and questions.
Message
Author
Alan Pershing
356 Fan
Posts: 67
Joined: Mon May 08, 2017 4:54 pm
Location: Atlanta

Furtive fuel leak

#1 Post 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!

User avatar
Mike Wilson
Classifieds Monitor
Posts: 11892
Joined: Tue Apr 15, 2008 4:37 pm
Location: SW Los Angeles

Re: Furtive fuel leak

#2 Post 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
Mike Wilson
Lomita, CA
'63 B coupe

Alan Pershing
356 Fan
Posts: 67
Joined: Mon May 08, 2017 4:54 pm
Location: Atlanta

Re: Furtive fuel leak

#3 Post by Alan Pershing »

Weber IDFs 40s.

User avatar
Mike Wilson
Classifieds Monitor
Posts: 11892
Joined: Tue Apr 15, 2008 4:37 pm
Location: SW Los Angeles

Re: Furtive fuel leak

#4 Post 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
Mike Wilson
Lomita, CA
'63 B coupe

User avatar
David Jones
Classifieds Moderator
Posts: 7392
Joined: Tue Mar 25, 2008 6:32 pm
Tag: I wish I knew as much as I think I know.
Location: Kentucky

Re: Furtive fuel leak

#5 Post 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.
If I had known I would live this long I would have pushed the envelope a little harder.
Cymru am byth
David Jones #9715

User avatar
Jim Clement
356 Fan
Posts: 1491
Joined: Tue Oct 26, 2010 10:46 am
Tag: 1957 356 A Coupe
Location: Calgary Alberta

Re: Furtive fuel leak

#6 Post by Jim Clement »

fuel pump / fuel pump gaskets ?
 

Alan Pershing
356 Fan
Posts: 67
Joined: Mon May 08, 2017 4:54 pm
Location: Atlanta

Re: Furtive fuel leak

#7 Post 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.

Alan Pershing
356 Fan
Posts: 67
Joined: Mon May 08, 2017 4:54 pm
Location: Atlanta

Re: Furtive fuel leak

#8 Post 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

User avatar
David Jones
Classifieds Moderator
Posts: 7392
Joined: Tue Mar 25, 2008 6:32 pm
Tag: I wish I knew as much as I think I know.
Location: Kentucky

Re: Furtive fuel leak

#9 Post 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.
If I had known I would live this long I would have pushed the envelope a little harder.
Cymru am byth
David Jones #9715

Alan Pershing
356 Fan
Posts: 67
Joined: Mon May 08, 2017 4:54 pm
Location: Atlanta

Re: Furtive fuel leak

#10 Post by Alan Pershing »

Great idea, I'll try that tomorrow after work.

User avatar
Doug McDonnell
356 Fan
Posts: 6108
Joined: Sat Apr 05, 2008 8:21 am
Location: Augusta,Michigan

Re: Furtive fuel leak

#11 Post by Doug McDonnell »

Out of sight - out of mind. Check the short piece of fuel line behind the fan housing.
1965 356C 2000 BMW 740i Sport 1967 Honda CL77 There is never enough time to do it right, but always enough time to do it over.

Alan Pershing
356 Fan
Posts: 67
Joined: Mon May 08, 2017 4:54 pm
Location: Atlanta

Re: Furtive fuel leak

#12 Post 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.

User avatar
Martin Benade
356 Fan
Posts: 12663
Joined: Wed Nov 23, 2011 10:52 am
Location: Cleveland, Ohio

Re: Furtive fuel leak

#13 Post 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.
Cleveland Ohio
62 Cabriolet
56 VW
02 IS 300
04 Sienna

Alan Pershing
356 Fan
Posts: 67
Joined: Mon May 08, 2017 4:54 pm
Location: Atlanta

Re: Furtive fuel leak

#14 Post 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.

User avatar
Wes Bender
356 Fan
Posts: 5066
Joined: Wed Aug 27, 2008 10:54 am
Location: Somewhere in the Gadsden Purchase, USA

Re: Furtive fuel leak

#15 Post 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.
Some days it's just not worth chewing through the restraints.....

Post Reply