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MG MGA - Intake Manifold and Carburetor Heat Shield

I recently had a problem with symptoms similar to Barry Bridgens. She would idle fine, but spit, sputter and hesitate under any load. Since I was planning to clean up the carbs in anticipation of adding my Gyles designed/Ash produced stub stacks I went ahead and pulled the carbs. It looks like my problem is just a cracked fuel float (fingers crossed).

In the process of getting ready to reassemble everything I happened to take a closer look at the carburetor heat shield and the mounting gaskets. Turns out that on my car the intake holes in the heat shield are not all that well aligned with the intake manifold. The bottom of the heat shield holes line up well but the top of the holes overhangs the manifold opening by a noticeable amount (very roughly 1/16 inch). Some of the mounting gaskets also have noticeable overhangs.

Before I pull the heat shield to do a bit of grinding to open the intake holes, does anyone have any thoughts regarding the potential impact of the overhang? Other than an electronic ignition, she is a stock 1500 with the original carbs.

John



John Backman

John,

The 1500 has a gasket on the back of the heat shield also. Does yours have them? See the tech article by Mike Ash in MGA! magazine this month for full details on this.

Peter.
P. Tilbury

Peter,

Yes, I have a gasket between the manifold and the heat shield, then gasket, spacer, gasket and finally carbs. All stacked in the correct order per Mike Ash’s tech article in MGA!. For those without access to the article, the writer was responding to an inquiry about seeing numerous cars with the spacer between the manifold and heat shield. This arrangement puts the heat shield in nearly direct contact with the carb bodies and the hot surface of the heat shield all that much closer to the float bowls.

It was the fact that the first gasket I put on the manifold was very clearly shading the intake that prompted me to look at the rest of the pieces. Don’t know the source of this particular gasket, but none of the new Moss gaskets I used shaded the intake. A razor blade made quick work of the odd gasket.

I used a felt tipped marker to indicate where the heat shield was overhanging the intake manifold. Then gently relived the area with an air grinder (not while on the car of course). It only took a few minutes. Now the intake bore is smooth all the way round. No idea if this will make any noticeable difference but it cannot hurt either.

John
John Backman

John, many, many years ago GPO (General Post Office) telephones used 5 hundredweight Morris Minor vans as part of their fleet for small works and line maintenance engineers. These vehicles were 'governed' by fitting a steel plate between the carburetor and manifold which had a hole in it much smaller than the bore of the carburetor. This plate also served as the anchor for the throttle cable, so it couldn't be removed. With this form of governing in place it would take half an hour to struggle up to 45 mph!
One Christmas period I was covering a colleague's call-out load for him while he spent the holiday with his family, and as his van had all the necessary tools on-board, I used that rather than my own van which was only equipped for maintaining telephone exchanges. On arriving home with the van on the first day, I was so sickened by the lack of anything resembling performance, I removed the restrictor plate and filed the hole in it out to the correct diameter. Boy was my friend surprised when he drove his van for the first time after his holiday!
Lindsay Sampford

Lindsay,

Great story! When I was in high school my Dad had a '68 midget with its own form of speed control. One cylinder had virtually no compression. No worries in southern California - it wasn't about going fast as it was being seen. No small feat in a midget.

These days we are obsessing over imperfections in 50 year old cars that were designed to only last 3 or 4 years.

John
John Backman

This thread was discussed between 05/11/2014 and 21/11/2014

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