What Causes This?
 

Some of you may remember that I was "given" this 750 CFM Holley by my original paint/body man. (Is it really a gift if he's taken the agreed money and done 1/2 the work, and that poorly? :-down) And then recently I found a guy on CL wanting to swap a 600 CFM Summit "4100" for a Holley 750, but he wanted a bolt & go carb, so today I pulled the Holley apart to put a kit in it. (Jim - If you've not answered the PM re Holley #'s don't bother. That's a moot point.) And, I was appalled at what I found.

Basically, the main body is delaminating as is one of the bowls. Here's one side of the main body, but the other side looked the same:


https://cimg3.ibsrv.net/gimg/www.for...eb966347bc.jpg


So, with nothing to lose I put it on the mill and took about .050" off, leaving it looking like this. But, the metal "feels" awful when milling it. There are spots that mill like they should and others that feel "loose", like the metal I'm milling isn't truly part of the body.

https://cimg4.ibsrv.net/gimg/www.for...15f4860e54.jpg


Obviously this body is well and truly junk. But my question is why? What happened to it? What could cause the metal to delaminate? Is this basically unheard of or???

Looks like there is a "coating" applied to the aluminium, is that what is peeling?

I don't think it is just a coating as it went pretty deep. At .050" down there was still crumbly metal below. It is like the casting is badly flawed. My first thought was water and freezing, but then I realized that freezing a bowl full of water would just cause the bowls to be warped. But it wouldn't hurt the integrity of the metal itself.

I have milled and filed several of these, and have never seen that before. I do know you need a fly-cutter to do it right and get a good finish. Do you have one? If you don't do you know about Enco? They are a good place to get machining tools cheap.

That's the one "flaw" with the Holleys and why they get a bad reputation sometimes. That surface in the picture has a tendency to warp, causing the gaskets not to seal.

I used to have a jig I made, a flat piece of thick aluminum with 4 countersunk holes that matched the threaded fuel bowl holes. I would bolt that to the opposite side of the carb(bowl off of course) and then use that to clamp it in the mill.

I do have a fly-cutter and toyed with using it. But just wanted to see what an end mill would do since I didn't make the plate you are talking about to clamp it to the table. However, even if I get the thing cleaned up there's still the scaling going on in the recesses. So even if I get the faces cleaned up there's still the possibility (probability?) of it flaking off and causing all sorts of problems.

Back to the question - what causes this? Is it a bad casting, and if so will it continue to do this? Or is it a surface issue caused by something caustic that was run into the bowls? (The latter doesn't seem possible since the faces shouldn't have been seeing any liquid as there's the gasket and metering plate sealing them off.) If this is just a one-off thing then maybe I could buy a used carb or body off ebay and fix it. But, if this is normal for this particular series of carb then buying another one might have the same problem.

Gary,
I have yet to figure out how to get to PM's and userCP on mobile. :o

I think this is due to the blend of pot metal used by Holley.
I know the newer -SA (Shined Aluminum) carbs don't do this, under the surface.
Look into the intra granular corrosion being caused by magnesium and zinc content, not the aluminum.

I have a lot of old holley carbs, and have worked with a lot of them. I have never seen this before, and I don't know what the cause might be. You should be able to get another body and be good.

Why put the time and $ into a carb that is eaten up on the inside?

Holley 750's are a everywhere.

This carb's metal is mealy. Very similar to the plastic on our door panels that are UV damaged. I think I could spend a lot of time milling the faces and still have ugly, and potentially serious cracks elsewhere. So, I might look into a new body, but that leaves one of the bowls having similar, although less severe, problems.

And that raises a question: Can I mix and match Holley bowls? This carb has the dual-inlet bowls, but I have a few single-inlet bowls that use the transfer tube. Can those be used? I might be able to cobble together a carb that way, although the other body I have is a spread bore design and those are VERY different.

Having said all that, Bruce/The Okie has offered me a 750 carb (thank you, Bruce!), and the guy with the Summit version of the 4100 is still looking, so I might still make that swap. I'm curious how that carb would perform on Rusty, and now that I have the AFR meter I might play with the three 600 carbs I would have (Holley, Summit, and Edelbrock) and see which one I can get to perform the best. And, by "perform" I don't mean just WOT. And Rusty should be a fair test bed as his C6 will provide consistent shifts and my trips up to see Dad provide a consistent environment - save for wind.

Yes, I agree. I put it on the mill more from curiosity than any plan to fix it since I could see places scaling that I can't get to.

But I am curious also about the idea of using different style bowls on Holley carbs since I now have an assortment of them. There are those that really seem to like the dual-inlet bowls and they might think a little 600 with those bowls is a huge carb.

I'm not sure if the transfer tube will pass a 750 body.
Holley uses single inlet up to 650cfm, and a 'log' for anything bigger.
I guess the transfer tube is limiting delivery to the secondaries, and Holley expects a 750 or larger carb is going to be run WFO.

I have heard that carb cleaner will attack the metal if you leave it in the carb cleaner too long.


Maybe that's what happened.

The dual inlet bowls are usually center hung floats. The transfer tube type bowls are usually side hung floats. Some people prefer one or the other depending on what they are doing with the car or truck they are going in.

I do think they make different length transfer tubes. I seem to remember a kit somewhere to convert the carb from one type bowl to the other. Let me look a little bit.

Looking at this link Holley Conversion Kits, Metering Blocks & Accessories - Free Shipping on All Orders @ JEGS

I remember now, some of the tubes are longer for carbs when the secondary metering block is installed. Some of the simpler carbs (4160) don't use secondary jets and a metering block, so that makes the tube shorter. Don't see why you can't interchange bowls, but I have never done it before.

Some race fuels will do this too.
Back in the day, there was an ELF fuel that would eat the bottom right out of an aluminum tank if you left it in overnight.

We would drain the tank, add a splash of 100LL and run the bike until it showed signs of poor running because it was not tuned for the Avgas.

At least we felt the system was purged of the devil's own cocktail.