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MG MGA - Carburetter Spacer

The carburetter spacers I have always used are 0.372" thick and I have always assumed they are the standard for the MGA. The pair I recently fitted with vacuum off-takes are only 0.30" thick. Interestingly I have never suffered vapour lock re-starting issues until I went for these slightly narrower ones, so I am left wondering if these small variations make a difference to carburetter heat soak. Then on Sunday I noticed that John Bray has a pair about 0.80" thick that he uses with his MGB carbs.

Question. Would fitting a pair of these extra thick ones make a difference to some of our problems we have been talking about recently?

I presume these thicker ones are readily available. Are they MGB standard?

Steve Gyles

My thermo spacer blocks are the thinner ones, about 0.3" thick, originally one inboard of the heat shield and one outboard of the heart shield. Some years ago I installed an addition one inboard, so now three total for each carburetor. The additional thermo block didn't help much. A much improved heat shield helped some, but still doesn't stop the fuel boiling in very hot conditions. The turbo blower fixed it entirely, so I figure to remove the extra spacer block next time the carbs are detached.
Barney Gaylord

You probably get more heat conduction via the studs than through the spacer.
Art Pearse

Hi Steve the inlet manifold and stud arrangement are different between the MGB and MGA so I don;t think the MGB spacers will fit on the MGA manifold.

Barnney's idea of increasing the number of spacers is an easy option if the existing studs are long enough to accomodate them.

Art's view about heat conduction is an interesting one.

It would be interesting to know why the MGB has the thicker blocks, it it just for heat reduction or is there a potential improvement with a longer inlet tract.

J Bray

Art is probably correct, and the more surfaces of gaskets you have the less heat transfer, Also, gaskets and spacers used to be asbestos. MGB needs the thicker spacers for clearance from the much better exhaust manifold besides, they had more room. Longer inlet tends to give better low end.

FR Millmore

Are the MGB inlet and exhaust manifolds a straight swap? i.e. are they compatible with the standard MGA carbs and exhaust?

Steve Gyles

MGA and MGB cylinder heads are physically interchangeable, so the manifolds will bolt up. MGB exhaust manifold will not clear the steering column on LHD MGA. To install MGB carbs on MGA you must use MGB intake manifold.

MGB intake and exhaust manifolds have two different thicknesses for the mounting ears. If you have a mismatch the heavy flat washers will not seat squarely. In that case you can machine washers with a step, or machine down the thicker manifold ears to match the thinner ones.
Barney Gaylord

Thanks Barney. I guess part of my query in my last post was based on the fact that I am using the 5-bearing 1800 but with All external MGA bits. I just wondered if perhaps I was limiting some of the benefits of that engine and maybe I should hang a few appropriate MGB bits!

Steve Gyles

Be aware that you cannot use an MGB exhaust manifold with an MGA intake manifold (and vice-versa)as they are different thickneses.
G T Foster

Meet Barney!

"MGA Exhaust" is a nebulous term. If you have a "stock MGA" exhaust you are loosing. See the discussion with my comments in the MGE thread Neil just revived in J Bray's manifold thread:,2069687,2069687%23msg-2069687

People generally use MGA manifold and carbs for the OE look, and it does not give much away. Best stock match is to use the 1622 needles etc., but any of them work fairly well for starters.
HS4 flow a tad better but that can be corrected by massaging the carb insides a bit. You already have most of the difference and maybe a bit more with you stub stacks.

FR Millmore

This thread was discussed between 14/08/2012 and 15/08/2012

MG MGA index

This thread is from the archive. The Live MG MGA BBS is active now.