Intake leak

[Art Ebeling]

My 11 starts but runs rough. Shorting out number Three or number four spark plugs make very little if any difference, numbers one and two make a great difference. Spraying brake cleaner thru a nozzle directly on the rear intake port wants to stall the engine. I put my hand above the carb to stop any spray that might be giving a false reading thru the carb. I have changed manifold gaskets and smeared with ultraseal, no difference. What I have not done is compare the intake and exhaust manifold for flatness. What is the best way to check if the manifolds need planing? Thanks, Art

[Norman Kling]

Two adjacent cylinders out of service could be caused by a sticky intake valve or a blown head gasket between the two cylinders. A compression test would be good to determine either. However since the spray seems to indicate a leak at the manifold. First thing I would check would be whether you had the glands installed between the block and the manifold. If they are not installed, your manifold could be off to one side or lower or higher than the intake port. Or the glands could be too wide and not allowing the manifold to compress the gasket. If the surface of the block and the surface of the manifold are flat you should not have a problem except for the above. The intake is not usually warped or eroded. The exhaust is more likely to be warped or eroded because of the high temperature of operation. But that should not cause rough running, just an exhaust leak.
Norm

[Art Ebeling]

I have the glands installed. I first used the original style copper rings and separate glands, then I switched to the three in one style copper sandwich style gaskets, again with the glands. I used a smear of Permatex ultra both sides each time. I checked that the glands were not too wide and not letting the manifold seat to the block. Same results each time. Number three and four plugs are dry black and sooty, that side of the manifold is dry. Number one and two plugs are brown and clean. Everytime I spray at the rear intake to block it slows or stalls the engine. At a loss here. Art

[Scott_Conger]

There have been some "too-thick" glands in the past. Norman is probably right in that assesment. That's sure where I would check. If this is a rebuilt engine, the port area may have been planed a little to remove rust pitting and exhaust erosion. If this is the case, all the more to suspect the gland rings. It is not easy to continually ding and damage the intake seals after you're aware it can happen. Not hard to do, but my guess is that you're being very careful now and aware of that. Look at the thickness of the gland rings.

As a quick check, you might wish to install a cheap, later manifold and rule out a crack in your original dog-leg manifold.

[Norman Kling]

How about the length of the bolts or studs which hold the manifold? Could they be bottoming out before the gasket is sealed? It could be just the one or two in that area. Norm