This one has me stumped- Carburetor leak🤷*♂️

[Anthony C.]

Hi , this is the situation guys .. I drive my 70 with a rebuilt carb and she runs absolutely great no problems . However when I park the car in my garage everything is fine . Strangely after about 2 weeks gas starts to leak from what seems to be from the top horn gasket but no sure . I guess my question is why would it take 2 weeks or so for it to start leaking and not right away 🤷*♂️ . Also this is the 2nd time it had happened over a 6 month period . Any help would be appreciated.

[Mark E.]

Re: This one has me stumped- Carburetor leak🤷*♂️

What carburetor do you have?

Assuming a Quadrajet, it is odd it leaks from the airhorn gasket since it's normally above the fuel level.

You might check float level and make sure the airhorn is flat. They often warp from over tightening.

A photo would help.

[Anthony C.]

Re: This one has me stumped- Carburetor leak🤷*♂️

What carburetor do you have?<br />
<br />
Assuming a Quadrajet, it is odd it leaks from the airhorn gasket since it's normally above the fuel level.<br />
<br />
You might check float level and make sure the airhorn is flat. They often warp from over tightening.<br />
<br />
A photo would help.

thanks mark airhorn looks tight but I will check .. Is there a torque spec for it. Thanks

[Mark E.]

Re: This one has me stumped- Carburetor leak🤷*♂️

thanks mark airhorn looks tight but I will check .. Is there a torque spec for it. Thanks

Much more than 5 mil from flat is a problem. Also check for a saturated float and leaking needle/seat.

The 4 hold down bolts are 14 ft-lbs. Over tightening the front bolts is a common cause of a warped airhorn and damaged body. Be sure to tighten the airhorn screws in the proper sequence and always use a new gasket. I don't know of a specified torque for these, but just a bit more than barely snug. The airhorn easily warps so use kid gloves. Recheck after a couple of heat cycles.

[Edward J.]

Re: This one has me stumped- Carburetor leak🤷*♂️

Anthony, is it possible that your fuel tank is pressurized after sitting? Cannot remember If your 70 has a vented gas cap.either way I would loosen gas cap and let the cap just sit on top of fuel tank loose. To see if this helps.

[Owen L.]

Re: This one has me stumped- Carburetor leak🤷*♂️

Anthony, is it possible that your fuel tank is pressurized after sitting? Cannot remember If your 70 has a vented gas cap.either way I would loosen gas cap and let the cap just sit on top of fuel tank loose. To see if this helps.

A pressurized system is where my mind went too. A leak that appears ~2 weeks after running seems really odd to me. I was wondering if the car has an electric fuel pump that might be getting voltage after the ignition is off. I believe the general rule on vented vs. non-vented (sealed) is if the car has a charcoal evap canister: canister= sealed cap, no canister = vented cap.

[Brett W.]

Re: This one has me stumped- Carburetor leak🤷*♂️

I have a 70 with a similar issue. I do not have a canister or a vent valve on the tank. Its a very original car but the previous owner did replace the tank. Not sure if he deleted canister and the vent valve as the new tank does not have the bracket. Has an original sealed gas cap and there is a lot of pressure build up after driving. Will be interested in the resolution.

[Owen L.]

Re: This one has me stumped- Carburetor leak🤷*♂️

I have a 70 with a similar issue. I do not have a canister or a vent valve on the tank. Its a very original car but the previous owner did replace the tank. Not sure if he deleted canister and the vent valve as the new tank does not have the bracket. Has an original sealed gas cap and there is a lot of pressure build up after driving. Will be interested in the resolution.

As I understand it, if there is no vent valve and canister then you should have a "vented" gas cap. The sealed caps were installed when the valve and canisters were put in as a vapor capture system to eliminate raw fuel evaporation directly to atmosphere.

[Anthony C.]

Re: This one has me stumped- Carburetor leak🤷*♂️

Much more than 5 mil from flat is a problem. Also check for a saturated float and leaking needle/seat.

The 4 hold down bolts are 14 ft-lbs. Over tightening the front bolts is a common cause of a warped airhorn and damaged body. Be sure to tighten the airhorn screws in the proper sequence and always use a new gasket. I don't know of a specified torque for these, but just a bit more than barely snug. The airhorn easily warps so use kid gloves. Recheck after a couple of heat cycles.

thanks mark i torqued hold down bolts I 14ft pounds and snugged all screws . Just have to wait and see if she leaks again thanks

[Anthony C.]

Re: This one has me stumped- Carburetor leak🤷*♂️

Anthony, is it possible that your fuel tank is pressurized after sitting? Cannot remember If your 70 has a vented gas cap.either way I would loosen gas cap and let the cap just sit on top of fuel tank loose. To see if this helps.

thanks Ed , I have non vented cap with charcoal canister .. I did loosen the cap after driving and a lot of pressure was released .. so far 4 days after driving and no smell. 🤞 however I do want to find this problem

[Anthony C.]

Re: This one has me stumped- Carburetor leak🤷*♂️

A pressurized system is where my mind went too. A leak that appears ~2 weeks after running seems really odd to me. I was wondering if the car has an electric fuel pump that might be getting voltage after the ignition is off. I believe the general rule on vented vs. non-vented (sealed) is if the car has a charcoal evap canister: canister= sealed cap, no canister = vented cap.

thanks Ed I ruled any electrical part because I have a battery delete with I engage when I park

[Anthony C.]

Re: This one has me stumped- Carburetor leak🤷*♂️

I have a 70 with a similar issue. I do not have a canister or a vent valve on the tank. Its a very original car but the previous owner did replace the tank. Not sure if he deleted canister and the vent valve as the new tank does not have the bracket. Has an original sealed gas cap and there is a lot of pressure build up after driving. Will be interested in the resolution.

thanks Brett , I have a non vented cap and canister , so I released the pressure 4 days ago and I am waiting to see if gas drips again 🤞

[Anthony C.]

Re: This one has me stumped- Carburetor leak🤷*♂️

As I understand it, if there is no vent valve and canister then you should have a "vented" gas cap. The sealed caps were installed when the valve and canisters were put in as a vapor capture system to eliminate raw fuel evaporation directly to atmosphere.

thanks Owen , I have a non vented cap with a canister. However I can understand smelling fumes , but dripping gas after 2 wks of being parked is very confusing