1972 Thermoquad - seeping fuel

[71_GreenFish]

Greetings fellow E-body enthusiasts-

Newer member to the forum. Still learning many things about fuel system and carbs, so I would consider myself a novice wrencher.

I'm looking to solve an issue with a '72 Thermoquad on my 340. I had the carb rebuilt by a local carb shop about 18 months ago (I re-installed the carb after the rebuild). I'm used the thick gasket for the carb to manifold install. It was a stock rebuild. Car is driven very sparingly and over time I've noticed some fuel seepage in several areas, and the smell of raw gas after shutting car off - within 15 minutes. This past weekend I noticed the most seepage. The main area of seepage is at the bottom of the carb near the throttle shaft on the left side (driver's side). I run ,y finger underneath the base that does not joins the intake manifold and feel gas. It doesn't leak a large amount but it does eventually drip enough (over about an hour) to form a very small puddle in one of he manifold buckets.

As noted, the carb was rebuilt by a reputable ( or at least I thought so) local shop, so I'm not sure if the issue is with the rebuild or the carb, and I don't anyone to be able to diagnose the problems based on the pics that I've uploaded, but if anyone has any ideas/suggestions, I would welcome those.

I'm tempted to have the carb rebuilt, by different carb shop, but not sure if it would sold the issue.

 

[moparlee]

Looks like it could be leaking all over the place. Does it leak at the accelerator pump shaft?
How does the car run?

 

[moparleo]

Throttle shaft leaks are not uncommon. The carb restoration rebuilders can rebush the base and the shafts were Teflon coated when new.
A regular shop doesn't normally do this precise of work. Any carb will seep slightly.
It is not like fuel injection where the throttle body only has air going through it.

Services

 

[71_GreenFish]

Moparlee: It appears there is seeping in several locations. The accelerator pump shaft area does appear to show some staining from dried gas, but the mail seepage appears to come from underneath the base of the card, near to or close to the throttle body shaft on the drivers side of the carb.

Moparleo: I've heard of rebushing the throttle shafts, so I'm assuming that another standard rebuild won't cure the problem if in fact the seepage is coming from the throttle shaft area? Any way to verify that the leak is from the throttle shaft? I've tried moving the shaft fore and aft to see if there is any play, and it seems tight.

 

[Chryco Psycho]

This is actually typical , newers fuels are very different from the fuels these carbs were designed for , the fuel is boiling in the carb from heat off the intake this will cause the fuel to spill out the venturiis & sit on the throttle plates & leak from the base .
My advice is to pull the intake & block the heat crossover in the intake using a piece of stainless or the old intake gasket , Cool carb also makes better heat insulators & can reduce carb temps by 100* or more , I would look into that also .

 

[71_GreenFish]

Chryco Psycho: I suspected this was the issue as I've also experienced a hard start after sitting for more than an hour after it has been run (no issue on cold start - fires right up). So I suspect a heat sock/vapor lock issue with the fuel boiling in the carb. Have you had any success with installing a vented fuel filter with a line going back to the gas tank? Any value is doing something like this, in your experience, to solve this issue? I've come across the suggestion in several online sources....here's a vid I came across.

 

[71_GreenFish]

I meant to say a vapor separator fuel filter

 

[Chryco Psycho]

That might help But if the needle & seat are closed the fuel has nowhere to go & will boil into the engine , my first move would be blocking the crossover port in the intake .

 

[71_GreenFish]

Sounds good ,Chryco. Thanks for your recommendation.

 

[i_taz]

Make sure the vent lever on the front pass side is working.

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