Just completed replacing/resealing the intake/exhaust manifold, with less than desirable results…

1968 Barracuda with 225 that is completely stock---Holley 1920, Auto Trans, Petronix conversion.
Background: Valves adjusted to spec last fall, timing checked, tune-up complete

Decided to do this job because I had an exhaust leak and a frozen heat riser with a broken spring. Car ran well prior – 60 mile trip just before I dismantled it. It had a slight cold drivability issue…very minor, not work chasing. It had been running very well.

Dismantled everything carefully.
Following some of the advise from a previous post…I ordered a new Dorman exhaust manifold (its so-so..) and the existing factory 1bbl intake. The Dorman unit comes with most new hardware
Ordered Remflex gaskets for the exhaust and the used the Dorman gasket with HyMar sealer for the intake. (I regret this now...:>)
Cleaned everything and followed the procedure(s) posted here as closely as possible. All bolts torqued to spec.
Reassembled.
Everything looks great---alignment of the intake and exhaust looks good.
Go to fire it up…kicks right on fast idle…touch the gas and it dies.

Will NOT idle at all----stalls has soon has you let off the gas.
Over an hour of attempts and getting the motor to operating temp did nothing.
Will only run at about 2000 RPM.
Checked torque on all bolts.
Checked/Replaced the vacuum hoses
Not a fuel issue
Ignition system is strong
Tried two different ‘working’ carburetors---same result. Using a known good carburetor.

At this point I have only to assume that intake did not seal somehow and I have a vacuum leak?

It’s difficult to diagnose as its almost impossible to keep running.

On the bright side, I think the exhaust leak is fixed…..

What am I missing?

Prior to ordering the REMFLEX intake gasket and dismantling it again (FUN!), I would like to verify the gasket is the issue.
Any other thoughts or suggestions are appreciated.

thanks

I sounds as though the exhaust manifold flange may be thicker than the intake manifold flange putting more clamping force on the exhaust manifold. The intake manifold needs to be thicker at the flange and receive more clamping force than the exhaust manifold. You should be able to see this if it's bad enough. Yes, I have had this happen to me. The quick fix is to find or make small shims (small flat washers may do) to go between the bridge washers and the intake manifold.

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Joshua

Plug pvc hose, that should slow it down some.

https://www.slantsix.org/forum/viewtopi ... it=exhaust This was bulletin about replacement manifolds. Instructions say to check hole in intake manifold, 27/64 drill bit.

Following this thread with great interest because I have the exact same issue.
Will start and idle really high and is pulling 18-19" of vacuum but will absolutely not idle below (at best guess) 2000 rpm. So to me the carb is fine (rebuilt Holley 2280) and the HEI upgrade is working as well.
Funny thing is I had it running and idling even with a stuck valve (as best as it would on 5 cylinders!).

By any chance did you tighten the intake to exhaust through bolts before you bolted them to the head? I did that once and got the same issue you're seeing. I leave the bolts loose until the manifolds are torqued to the head, then tighten them.

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Official Cookie and Mater Tormentor.

I know I did not do this. I drilled it 3/8. It had very little slop. I assembled everything finger tight. Installed the assembly to the engine. Installed all of the nuts/washers finger tight.

First I torqued the 3 exhaust to intake bolts to 22 ft lbs.
Second, I torqued the stud/nuts to approx 12-14 ft lbs.

Did I do this backwards?
I cannot see anything that visible.

Should I try loosening everything and re-torque in a different sequence prior to doing a full removal?

I am leaning toward dismantling it all, re-drilling the one hole and using a Remflex gasket....but if i can salvage this install, I would like to.

Thanks for all the reply's. So much knowledge here!

Yes and yes.

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Official Cookie and Mater Tormentor.

Yup, this is regrettable. It is very much worth your while to get the Remflex gaskets for the manifolds-to-head and intake-to-exhaust junctions. Hylomar (or other goop) is not a good idea with the Remflex gaskets.

If the single inboard stud for the intake-to-exhaust manifold junction fit through the intake manifold on your first install, then there is no clearance issue and no need to redrill anything.

Do you find evidence of a vacuum leak at the higher RPMs the engine will run at? Sputter/poof sound effects at the exhaust? An intake leak big enough to prevent idling should be big enough to make itself evident at the speeds the engine will run at. Have you tried spraying carburetor cleaner at the intake runner-to-head junctions to see if the way the engine runs changes at all (indicating cleaner getting sucked in)?

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

Slightly off center,top drill bit number 52 bottom bit 53. Room for movement any direction.