"66 Holley carb leaking at idle transfer slots

[Mike Z.]

Re: "66 Holley carb leaking at idle transfer slots

Maybe I am not sure what you mean by "Transfer Tube". I am familiar with the idle transfer circuits slots or holes, which are just above the butterfly at idle position. I thought originally you were talking about what I know as Discharge Nozzles (a common problem)- the round part sitting squarely over the butterfly in the middle of the venturi. However, to follow up on my initial comments and to respond to others, I believe you will find:
1) The bowl needle and seat should hold any pressure from the pump, so I do not believe the issue is the mechanical pump
2) Issue with needle/seat or too high float level adjustment will result in leakage into the venturi area via the vent tube
3) Issue with pump nozzle leakage into venturi is due to faulty accelerator pump nozzle needle, weight or check ball
4) Issue with leakage into venturi from discharge nozzle (primaries or secondaries) is a gasket seal issue (main body to jet plate), as I first indicated and suggested surface check. I would believe if your issue truly is the idle transfer slot, it also is a gasket seal problem.
The above is fundamental but sometimes simply works.
Mike

[Robert B.]

Re: "66 Holley carb leaking at idle transfer slots

Maybe I am not sure what you mean by "Transfer Tube". I am familiar with the idle transfer circuits slots or holes, which are just above the butterfly at idle position. I thought originally you were talking about what I know as Discharge Nozzles (a common problem)- the round part sitting squarely over the butterfly in the middle of the venturi. However, to follow up on my initial comments and to respond to others, I believe you will find:
1) The bowl needle and seat should hold any pressure from the pump, so I do not believe the issue is the mechanical pump
2) Issue with needle/seat or too high float level adjustment will result in leakage into the venturi area via the vent tube
3) Issue with pump nozzle leakage into venturi is due to faulty accelerator pump nozzle needle, weight or check ball
4) Issue with leakage into venturi from discharge nozzle (primaries or secondaries) is a gasket seal issue (main body to jet plate), as I first indicated and suggested surface check. I would believe if your issue truly is the idle transfer slot, it also is a gasket seal problem.
The above is fundamental but sometimes simply works.
Mike

Mike, I agree with your comments. I just couldn't believe that the metering block was warped enough to cause a leak, but in fact it was. Double gaskets have stopped the leak - now the question is do I leave the two gaskets in, or try to file or grind (or machine) the metering block flat?

Bob

[Steve G.]

Re: "66 Holley carb leaking at idle transfer slots

Maybe I am not sure what you mean by "Transfer Tube". I am familiar with the idle transfer circuits slots or holes, which are just above the butterfly at idle position. I thought originally you were talking about what I know as Discharge Nozzles (a common problem)- the round part sitting squarely over the butterfly in the middle of the venturi. However, to follow up on my initial comments and to respond to others, I believe you will find:
1) The bowl needle and seat should hold any pressure from the pump, so I do not believe the issue is the mechanical pump
I think what that poster was referring to was the fuel that's trapped in the line between the needle and seat and the poppet valve in the pump after the engine has been shut off. Fuel pump pressure is regulated on the other side of the poppet. That fluid is trapped and as it heats up will expand and push the needle off it's seat. Very small and insignificant amount of fuel.
2) Issue with needle/seat or too high float level adjustment will result in leakage into the venturi area via the vent tube
True that it will come out the vent tube, but only if the leak into the bowl is greater than what can leak out through every other orifice below the fuel level, all of which are lower than the vent tube. That is not often the case. Usually float/needle issues are smaller leaks and the fuel will never reach the top of the vent, but will be dripping from the idle circuit and main circuit. Real common in the 70's with paper inlet filters and Q-jets.
3) Issue with pump nozzle leakage into venturi is due to faulty accelerator pump nozzle needle, weight or check ball
4) Issue with leakage into venturi from discharge nozzle (primaries or secondaries) is a gasket seal issue (main body to jet plate), as I first indicated and suggested surface check. I would believe if your issue truly is the idle transfer slot, it also is a gasket seal problem.
The above is fundamental but sometimes simply works.
Mike

Just to help avoid misdiagnosis.

[Timothy B.]

Re: "66 Holley carb leaking at idle transfer slots

Robert,

I am hesitant to add any more to this post except to hopefully explain and show where your problem likely originates. If you look at the center picture of the metering block fuel is draining from hole #24 and a little from #25 and because of a bad gasket press seal, it is running to hole #4. The fuel will run into #4 and out the main body transfer slot until the main well #21 (in the bottom picture) is empty. At idle and low speed the main well fuel level is equal to the height of the float level FWIW.

These metering blocks usually warp in the area around and to the left of the #19 in the center picture.

[Mike Z.]

Re: "66 Holley carb leaking at idle transfer slots

Robert, I am glad the double gasket worked for you and it maybe fine for a long duration. However, I believe you will ultimately find; if the jet plate is warped, the main body of the carb probably is also. Actually truing up the surfaces is not difficult, but partial or entire tear down is required and work on it off the car. While you have the carb apart, bet if you check the secondary main body surface and the metering plate, they also need attention-damn near impossible to find anyone that carries metering plates and they ain't cheap, but you can straighten (soft aluminum jaws in a vise worked for me) them and true them (on gasket surface, using same technique as other surfaces)-take your time. Checking these surfaces has become a normal part of rebuilding carbs for me-if they are not a problem at initial start up, they probably will be down the road-I don't like come-backs. Best of luck,
Mike

[Robert B.]

Re: "66 Holley carb leaking at idle transfer slots

Robert,

I am hesitant to add any more to this post except to hopefully explain and show where your problem likely originates. If you look at the center picture of the metering block fuel is draining from hole #24 and a little from #25 and because of a bad gasket press seal, it is running to hole #4. The fuel will run into #4 and out the main body transfer slot until the main well #21 (in the bottom picture) is empty. At idle and low speed the main well fuel level is equal to the height of the float level FWIW.

These metering blocks usually warp in the area around and to the left of the #19 in the center picture.

That picture is very helpful, could you send me a higher resolution copy? My email is bob@behlman.us

Thanks,

Bob

[John H.]

Re: "66 Holley carb leaking at idle transfer slots

Bob -

DO NOT remove (grind, file, etc.) any material from that metering block - the only cure is to flatten the block with a press fixture designed just for that purpose; most of the expert "carb guys" (like Eric Jackson, www.vintagemusclecarparts.com) have that tooling and expertise.

[Steve G.]

Re: "66 Holley carb leaking at idle transfer slots

Robert,

I am hesitant to add any more to this post except to hopefully explain and show where your problem likely originates. If you look at the center picture of the metering block fuel is draining from hole #24 and a little from #25 and because of a bad gasket press seal, it is running to hole #4. The fuel will run into #4 and out the main body transfer slot until the main well #21 (in the bottom picture) is empty. At idle and low speed the main well fuel level is equal to the height of the float level FWIW.

These metering blocks usually warp in the area around and to the left of the #19 in the center picture.

I think you'll find that the pattern of the warpage is concave from the bowl screw holes inwards. It comes from reusing old gaskets and overtightening the bowl screws. Doubling up the gaskets it a pretty sure way to increase the warpage.

[John D.]

Re: "66 Holley carb leaking at idle transfer slots

Have you tried wiring open the heat riser valve temporarily to see if it helps ? It worked wonders on my 67 L79 for hot start and peroclation issues.

[Robert B.]

Re: "66 Holley carb leaking at idle transfer slots

Bob -

DO NOT remove (grind, file, etc.) any material from that metering block - the only cure is to flatten the block with a press fixture designed just for that purpose; most of the expert "carb guys" (like Eric Jackson, www.vintagemusclecarparts.com) have that tooling and expertise.

Thanks, John -

I appreciate your advice - another question - where can I find a reference for what Holley carburetor list numbers and metering blocks were used on which cars? Or is that even available?

Bob

[Robert B.]

Re: "66 Holley carb leaking at idle transfer slots

Have you tried wiring open the heat riser valve temporarily to see if it helps ? It worked wonders on my 67 L79 for hot start and peroclation issues.

No, I haven't tried that, John. My problem was clearly caused by the carb leaking a lot of fuel into the manifold after shutdown, essentially flooding the engine. When I stopped the leak, the problem goes away. It starts immediately whether it's hot or cold.

Bob

[John H.]

Re: "66 Holley carb leaking at idle transfer slots

Thanks, John -

I appreciate your advice - another question - where can I find a reference for what Holley carburetor list numbers and metering blocks were used on which cars? Or is that even available?

Bob

Bob -

Somewhere there's such a carline-specific application cross-reference, but I don't have it.