Expert: Brad Sears - 10/17/2011

Question
QUESTION: I have a 1951 Chevrolet 3100 with a 235 ci motor. I have set the timing and idle properly but I cannot get it to idle properly. I need to keep the choke out when I am running the truck both cold and warmed up. When I push the choke all the way in it sputters and dies.

I read a previous post that diagnosed a similar problem with a vacuum leak. Looking at where the intake manifold attaches to the block there are black carbon marks on the gasket. There are similar marks on the exhaust manifold gasket as well but more pronounced on the intake. This problem started after I did a head job a few years ago. Does the carbon on the gasket indicate a potential vacuum leak which could be the root of this problem?

Any other thoughts on the matter would be helpful, I want to make sure I am exploring all options.

I have attached a picture for reference. I hope this helps.

Thank you,

Brandon McGill

ANSWER: I have a question. When you did the head job and re-installed the manifold on the head, did you install the metal rings in the intake runners that help align the head with the intake manifold? If those were not put back in then it is almost impossible to prevent intake vacuum leaks.To check for intake vacuum leaks, run the engine at the best idle that you can get. Then spray carburetor cleaner or either starting fluid around the intake to cylinder head joints. If the idle changes then there is a vacuum leak.

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QUESTION: What do those metal rings look like? Do they come with a gasket set? Do you have a picture?

Thank you,
BM

Answer
I went through all of my reference material and cannot come up with a picture of them. They are more like a sleeve that aligns the head with manifold.  remember buying gasket sets in the past with them included but I just checked with Chev's of the 40's and their gasket set does not include them.