Hello, new to register to the forum,
This is my first post but I read for tech information.

I have a exhaust leak on the manifold of my 71 truck.
I removed the intake/exhaust manifold and the gasket is in good condition with no signs of leakage.

When looking at the choke riser on the exhaust manifold from inside the manifold about 1/3 of the factory cast material is missing.

This appears strange to me because all choke thermostats should be enclosed.

It appears that all that is sealing the exhaust is the is the choke thermostate inner sheild.

I reassembled the truck and still have the same leak so....

I can place my hand at the rear of the choke thermostat and feel exhaust pressure with the obious signs of a leak.

I believe this is an failed casting on the exhaust mainfold, and there is no cracks or black signs of leakage on any of the exhaust runners.
I painted the motor 1 year ago so the intake is still blue but the exhaust is a flat white so any cracks should be real obivous.

Thanks for any help I think that I need to start hunting a exhaust manifold.

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1971 D100 SWB Step side, 225, 3 on the tree, 3.91 gear

Welcome onboard.
For 1970, 1971 and 1972, the slant-6 exhaust manifold had an actual hole in the casting instead of the cast-in iron "well" or "cup" area where the choke thermostat goes. There is a sheetmetal cup (officially "stove") that gets dropped atop this hole, with a gasket, then the choke thermostat goes on, and two bolts hold the whole thermostat-cup-gasket sandwich onto the manifold.

After awhile, the gaskets go away and leak. With extremely long service, the inner cup (stove) itself can fail and leak. Thermostats can still be had new; gaskets can be made by hand if needed, but the actual cups are getting a little tough to find.

'60-'69 and '73-up exhaust manifolds use a cast-in-place well, the type you're used to seeing.

You may want to make a blockoff plate and install it with a gasket, then bolt one of the electric chokes atop the new blockoff plate.

I believe this is an failed casting on the exhaust mainfold, and there is no cracks or black signs of leakage on any of the exhaust runners.
I painted the motor 1 year ago so the intake is still blue but the exhaust is a flat white so any cracks should be real obivous.

Thanks for any help I think that I need to start hunting a exhaust manifold.[/quote]

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

I may still have my old choke pocket and choke assembly from my old '72 manifold. The gasket is toast. I'll check for you and let you know if intrested. This will be a good time to find a '73 up manifold that does not have the choke hole in the exhaust runner, and is a stronger casting as well.

Welcome onboard.

For 1970, 1971 and 1972, the slant-6 exhaust manifold had an actual hole in the casting instead of the cast-in iron "well" or "cup" area where the choke thermostat goes. There is a sheetmetal cup (officially "stove") that gets dropped atop this hole, with a gasket, then the choke thermostat goes on, and two bolts hold the whole thermostat-cup-gasket sandwich onto the manifold.

After awhile, the gaskets go away and leak. With extremely long service, the inner cup (stove) itself can fail and leak. Thermostats can still be had new; gaskets can be made by hand if needed, but the actual cups are getting a little tough to find.

'60-'69 and '73-up exhaust manifolds use a cast-in-place well, the type you're used to seeing.

You may want to make a blockoff plate and install it with a gasket, then bolt one of the electric chokes atop the new blockoff plate.

Actual source for electric choke kits is Randy Rymal, and he can be reached at rymals@chartermi.net .

Thanks for the tip on the choke kit, but the manual thermostate actually works real good,

It must be because 1/3 of the manifold apperars to be missing, there is not a hole.
I am serious when I say that the entire front portion of the "stove is exposed to exhaust gas.

The "cup" is excellent condition and the choke thermost is new works fine.

With this problems with this manifold I assume have fabricat a 1/8 plate and either put an electric or a manual choke on it.

But the question is has anybody seen such a large hole over the choke?

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1971 D100 SWB Step side, 225, 3 on the tree, 3.91 gear

So what that manifold is just to have a small hole?

What size? Just curious.

Thanks for the help, I think I can find one locally.

I want to keep my old truck as original as it came because I promised it to the original gentlemen, that I would not V-8 it.

P.S. My Dad tought me to drive on a identical 70 but he traded in 78 for a power wagon (which he still has 260,000 miles).

I will teach my 5 year old on on the 71 when he is old enough.

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1971 D100 SWB Step side, 225, 3 on the tree, 3.91 gear