JoeCool66

I have a problem. The iron intake on my ’66 327/300 keeps getting what looks like exhaust burn marks on the left side between the carb and the valve cover. To the best I can deduct, the black ash marks are coming from under the carb. I’m guessing my downshifting and using the engine to slow down the car isn’t helping the situation.

The "hot-slot" slit under the carb has had the holes tapped and sealed with allen-head NPT plugs…not leaking there. What’s under the carb is as follows: paper gasket on the manifold; thin metal gasket; 1/4” isolation spacer then aluminum heat shield (both from Holley); paper gasket then the carb.

I’ve had the car a few yeas and this seems to be a recent development. I’m getting tired of cleaning and repainting the manifold (you can see the cracks in the paint are from heat and too many layers)…. Any suggestions?

Joe

Plasticman

Is your heat riser stuck closed (passenger side at bottom of exhaust manifold)?

If not, then you might want to wire it so it is "always" open (since you are in FL, you really don't need it "closed").

What you are seeing is hot exhaust gases flowing across from one side of the engine to the other via the exhaust crossover. That crossover was for quicker engine warmup. Very common problem of burning paint off the intake on that area.

Plasticman

Mike Geary

Joe:

for what it's worth, I recently discovered that the iron manifold on my '65 was severely warped on the carb mounting surface.

The sides had shrunk down from all the heat cycles through the exhaust crossover. So much so that the gasket was not sealing on the sides.

Might be related to your symptom.....

ps: The head mating surfaces were also warped up in the middle, which is why I was getting oil pooling at the manifold edge. It wasn't the bolts not being sealed or fully torqued.

Mike

66since71

Tapping and plugging the hot slot at the carburetor flange doesn't keep the air between those plugs and the exhaust manifold from heating up. You can get a little more protection by closing off the passage at the intake manifold gasket. They used to sell specialty gaskets to do the job (try Summit). Or you can mask it with some stainless steel shim stock. Beer cans used to be thick enough to do it, although aluminum. (you can guess How I know that?) Bend a slight L shape to it to keep the shim from dropping into the lifter valley.

Edit. You know on that manifold, I think there is still a passage UNDER the bottom surface of the manifold, that remains open even with the hot slot plugs. It's protected from oil splash and coking by a heat shield? The only solution for that one is the shim. Be sure to block the heat riser on the right side open.

Harry

MikeM

I believe you are using the wrong carburetor base gasket against the manifold. The right gasket covers the end of the heat slot, unlike your picture.

JoeCool66

Wow...thanks for the quick replies..


Plasticman - My heat riser is wired open... but I haven't check in a while. I'll confirm.


Mike - I'm getting the same oil pooling at the manifold edge. Hummmm.... Need to look into this

Harry - I have a feeling this manifold id coming off soon. I'll look into blocking those passages.

Thanks guys!! I'll let you know

JoeCool66

Mike, you mean that thicker, heat resistant gasket? ...has the opening for the heat slot? Mine had worn down and had a section missing. Didn't replace it thinking it wasn't needed since I plugged the slot. Did I do bad?

66since71

I should have mentioned that blocking the passages will affect choke operation. You may have to adjust it to "always open", and accept some cold weather starting issues.

Harry

JoeCool66

Good tip but no issues here.. I'm running an electric choke
BTW .. I live in Florida. Cold weather starting is not exactly a concern

MikeM

I don't know what kind of Dagwood stack of gaskets you have on there but I believe the correct gasket should not show any of the manifold casting containing a heat slot. Looks like your gaskets are for a manifold without the heat slot. There is a difference.

It has been about 50 years since I made the mistake once of using the wrong gasket because that all I had and I got an exhaust leak at that point.

Yes, I do realize you said you had the ports into the exhaust plugged.

MikeM

Now that I'm on a different computer screen, I can see much better the stain you're talking about. That looks like maybe gasoline dripping out of the throttle shaft? Is it?

JoeCool66

Now that's funny!!

JoeCool66

Okay, let me see if a gas leak is happening here. The dark, burned stains made me think exhaust but let me do some tests.

Can someone enlighten me on a recommended gasket stack? This is not stock since I would like to retain the 1/4" block and heat shield since I drive this thing and I believe that helped on peculation and hot restarts.

Thanks.... Joe

MikeM

If you're having hot restart problems, your carb may be boiling over inside the throat and running down to the throttle shaft and seeping out there. The gaskets have nothing to do with causing this problem.

So the hot restarts and the stains on the manifold could very well be related.

JoeCool66

Thanks Mike, I appreciate the feedback.. I got rid of my hard starts by adding the shield and gaskets and all was good for a couple of years. Now the burn marks appear. Maybe my leak is getting worse after 2 years of wear....

If I take the carb off would I feel play in the shaft? How can I tell I have a leak? Can it be sleeved?

JoeCool66

Forgot to mention that in my earlier checking, I put a bit of tape along the seam of the carb to the manifold (also the valve cover seam). After driving a bit I saw the tape along the valve cover intact but the tape under the carb had blown off. Made me thing I'm getting back pressure coming out under the carb. I'll check further.

thanks, Joe