66, L-79 Carb problems

[Gary N.]

I have the original 4160 Holley on my L-79 66 coupe. I had it restore some years ago and it still looks new. I recently started having problem when I started it. It ran very rough until it completely warmed up. I pulled it apart and found that it had a bad power valve so I replace it and also replaced the accelerator pump while it was apart. I put in new metering gasket and a new bowl gasket also. The inside of the carb was spotless. I also noticed that there was a lot of gas setting in the intake manifold when I took the carb off. I also noticed the front bowl was empty. I started it up and it ran better, but when it set overnight the front bowl would be empty the next morning and the gas had emptied out of the front bowl into the intake manifold again. I had no visible leaks on the outside, all the gas was leaking to the inside. I did not pull off the base plate and replace it's gasket or any parts associated with it. Is there anything there that might cause the gas to drain out of the front bowl into the intake? I have a rebuild kit for it if needed, but I was just wondering if anyone has ever had a similar problem and what caused it and how to fix it. I know that the methanol gas also causes problems.
Thanks

[Keith B.]

Re: 66, L-79 Carb problems

I would double check the transfer tube and the well plug on the front bowl

[Larry M.]

Re: 66, L-79 Carb problems

That was one of the issues I had on my 1967 L79 with Holley #3810 carb. Engine would run fine, but on the rich side. After sitting overnight the fuel from the front bowl would drain onto the intake manifold. I ASSUMED that the accelerator pump screws were loose or perhaps a cut/tear in the front bowl gasket.

During the rebuild I found a pin hole in the accelerator pump diaphragm due to age and wear. Maybe also from using some ethanol gas over the years. But it has been 25+ years without touching the carb.....so I knew it needed some help. I also found what I believe were one or two of the small vents plugged or restricted from sludge and dirt build-up over time.

I completely rebuilt the carb a few weeks ago. Everything rebuilt or replaced and everything checked out. All problems appear to be fixed and car runs the best I remember it.

Larry

[Gary N.]

Re: 66, L-79 Carb problems

Larry, Thanks for answering. As stated, I replaced the accelerator pump diaphragm but that didn't help. I would also think that if the accelerator pump diaphragm had a hole in it that gas would leak externally from the pump cover. Did you soak your carb in cleaner when you rebuilt it? Mine is leaking internally down into the intake manifold and when I try to start it, it is almost flooded with gas that has leaked down in to the manifold. It appears that the front bowl is loosing all its gas thru the carb when it sits overnight. The rear bowl is retaining it's gas as when I take out a bottom rear bowl screw gas comes out.

Keith, The transfer tube is not leaking, I put new O-rings on both ends and if you are referring to the lead plug on the front bowl, it is not leaking. As I stated I am loosing gas internally.

[Larry M.]

Re: 66, L-79 Carb problems

Gary:

This is a mystery to me...........but I am very interested in the solution. It may have been my problem as well.

As stated, the carb ran rich, and had starting issues when warm/hot with (partial) flooding. When I pulled my carb I had raw fuel in both runners of the intake manifold. But I could also see fuel dripping from the front and rear boosters.........but much more from the front. I assume that this happened due to one or more of the small venting plugging and creating some internal pressure, pushing the fuel thru the boosters.

No, I did not dip the carb or any of the parts into carb cleaner. I used raw gas for cleaning as best I could, and then used Berryman carb cleaner in a spray can to spot clean as needed.......always doing a final rinse in raw gas. I had very little gasket material that did not easily remove, so I was lucky in that regard. A small brass wire brush and a few new razor blades took care of the stubborn gaskets. The rebuild instructions I had said do not dip the carb body and throttle plate in carb cleaner due to soft throttle shaft bushings/seals (i.e. polyethlyene/polyproplyene, or perhaps a version of teflon)

Now, after the rebuild and rodding out all the vents with thin wires, I have no more fuel visible at the boosters. Car starts and re-starts easily at this time.

I purchased the spray cans of electronic duster with the thin red straws to help blow thru all the passages in the carb. Having the thin straw really helped with this. I also would that if I invert the can, it will discharge a bit of liquid.......which quickly vaporizes.........and it really blows out the internal passages. But it also gets very cold due to the vaporization, so I limit this to about 1 second bursts. These electronic duster cans contain a refrigerant similar to R134a........that is all they are.

Larry

[Gary N.]

Re: 66, L-79 Carb problems

Larry,
Our problems sound very similar with the raw gas in the intake runners and the rich burning. It was burning my eyes in the garage. I did notice the top of the throttle plates were also a little wet, but did not see dripping. I also had very little sticking gasket material to contend with. Did you notice that the front bowl was completely drained after setting for a long period? I will get a can of Berryman carb cleaner and do the same with the metering block vents. Where did you get the electronic cleaner, I may try to get some also. I'm going to replace the front inlet valve and also the idle mixture screws since I have new one in the rebuild kit. I will have replaced all the parts in the front bowl and metering block at this point. My rear bowl seems to be holding its gas ok so I'm not going to take it apart again. I also noticed raw gas on top of and under the intake to carb gasket. Not sure why that is happening. The carb to intake bolts were tight? Thanks for your input, I'll keep trying. I also found some good pictures of the Holley metering block and bowl on the Holley web page and they helped me understand how and where the gas goes.

[Larry M.]

Re: 66, L-79 Carb problems

The electronic duster is available at hardware stores, and probably Lowes and Home Depot. A computer store should also have. Mine is called CRC DUSTER.........dust and lint remover.

The secret I found was inverting the can to get the liquid and give 1 sec bursts. It really provides a good powerful purge that you can see (due to the cold temp and vaporization). Not cheap at about $7-8 a can.....but effective.

Larry