Help! Leaking Holley Carb
 

I have a 750 Holley that has developed a leak through the base of the carb. Fuel is running out though a hole in the base, beside the base screw. This hole goes up into the area behind the power valve. I have change the power valve and changed the power valve gasket and when the fuel goes into the fuel bowl then fuel start to run out this hole. Any idea how to fix this?

Added a photo. This is the front, primary. of the carb. The cavity is where the backside of the metering block, with head of power valve goes. The hole to the right is threaded and is where one of the base plate screws go in. The hole to the left is where the fuel is running through and coming out the base of the carb.

Re: Help! Leaking Holley Carb
 

Next to the middle-front base plate screw?
That sounds like the passage that sometimes has an anti-backfire valve to protect power valves from blow-out. If it's not the power valve or its gasket leaking, only other things I can think of is the metering block gasket or casting issue. Double-check the metering block & main body gasket surfaces for any debris. Wouldn't hurt to check for casting warpage, but I've never seen that problem come up.

Re: Help! Leaking Holley Carb
 

Is this the hole you're talking about, Chris?

It's the vacuum port for the power-valve, so I'd make sure the valve and gasket were good. The metering block itself could have a bad gasket but I agree with Myron that it's unlikely to be warped badly enough to leak.

I also think that the later model Holley's were modified with a o-ringed transfer tube for the accelerator pump shot through the metering block and of course the gasket was changed to accommodate it. If you use that gasket with the older metering block you'll get a leak for sure!

Good Luck finding the problem!

Lew

Re: Help! Leaking Holley Carb
 

Lew, that is exactly where the fuel is running out of the base. I am going to change all of the gaskets, put a power valve block off plug in the metering block instead of a power valve and see what happens. I've never seen this either thanks for the help.

Re: Help! Leaking Holley Carb
 

Someone, I forget who makes a small tube with O rings on both ends of it to be use on the vent hole at the top of the power valve cavity. You would have to drill both the carb body and the power valve block to fit this tube with the O rings. That could possibly be where your having problems?

Re: Help! Leaking Holley Carb
 

I sounds like you have the wrong metering plate gasket.

Re: Help! Leaking Holley Carb
 

I think Phillip has the correct answer here, If it isn't the power valve itself. If you replace the power valve with a plug remember to re jet accordingly. Damn Holley's! Jim

.

Re: Help! Leaking Holley Carb
 

I've seen a few that have had the bowl screws tightend too tight repeatedly and cause the main body to pull in at the screw thread area. It keeps the gasket from sealing in the middle. Run a "new" very fine toothed flat file over the carb body and then a very fine sanding block to make sure the gasket surface is flat. Don't try to "Mill" it with the file, just take out any small imperfections. I have had to put a few in my mill and make a cleanup cut to get them flat.

Re: Help! Leaking Holley Carb
 

I'm with Phil and Jim.....There are several different metering block gaskets.

Carefully inspect Gasket to block for conforming to all Holes and Shapes.