Help! Leaking Holley Carb

chris3racing · 01-29-2012, 09:57 AM

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.

Myron Piatek · 01-29-2012, 10:42 AM

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.

Lew Silverman · 01-29-2012, 11:07 AM

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

chris3racing · 01-29-2012, 11:12 AM

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.

Terry Cain · 01-29-2012, 11:38 AM

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?

Phillip marvetz · 01-29-2012, 12:36 PM

I sounds like you have the wrong metering plate gasket.

Jim Wahl · 01-29-2012, 01:51 PM

Quote:

Originally Posted by Phillip marvetz

I sounds like you have the wrong metering plate gasket.

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

.

Adger Smith · 01-29-2012, 03:23 PM

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.

GTX JOHN · 01-29-2012, 09:18 PM

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.

01-29-2012, 09:57 AM	#1
chris3racing Senior Member Join Date: Mar 2008 Posts: 528 Likes: 0 Liked 0 Times in 0 Posts	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. Attached Thumbnails Last edited by chris3racing; 01-29-2012 at 11:05 AM. Reason: add photo

01-29-2012, 10:42 AM	#2
Myron Piatek VIP Member Join Date: Nov 2001 Location: Florida Posts: 1,542 Likes: 34 Liked 138 Times in 51 Posts	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.

01-29-2012, 11:07 AM	#3
Lew Silverman VIP Member Join Date: Mar 2010 Location: Newport News, VA Posts: 1,435 Likes: 371 Liked 129 Times in 59 Posts	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 Attached Thumbnails __________________ Lew Silverman #2070 "The Wagon Master" N/SA Last edited by Lew Silverman; 01-30-2012 at 12:57 AM. Reason: added another possible cause

01-29-2012, 11:12 AM	#4
chris3racing Senior Member Join Date: Mar 2008 Posts: 528 Likes: 0 Liked 0 Times in 0 Posts	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.

01-29-2012, 11:38 AM	#5
Terry Cain Senior Member Join Date: Feb 2008 Location: Georgetown, Indiana (close to Louisville, KY) Posts: 778 Likes: 530 Liked 231 Times in 107 Posts	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? __________________ Terry Cain ???? STK tcain19689585@gmail.com

01-29-2012, 12:36 PM	#6
Phillip marvetz Senior Member Join Date: Oct 2008 Location: Lynden ,WA Posts: 820 Likes: 0 Liked 3 Times in 3 Posts	Re: Help! Leaking Holley Carb I sounds like you have the wrong metering plate gasket. __________________ 2009 V/SA Record Holder

01-29-2012, 03:23 PM	#8
Adger Smith VIP Member Join Date: Dec 2001 Location: Texarkana Ark/TX Posts: 2,446 Likes: 575 Liked 880 Times in 311 Posts	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. __________________ Adger Smith (Former SS)

01-29-2012, 09:18 PM	#9
GTX JOHN VIP Member Join Date: Jun 2009 Location: Boulder City, Nevada 89005 Posts: 2,736 Likes: 2,808 Liked 2,488 Times in 698 Posts	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.