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MG Midget and Sprite Technical - Show me your carb heat shields

...please! The Frog is occasionally afflicted by a refusal to start when hot having sat for a little while. I'm guessing this is due to fuel vaporisation in the Weber 45, so I need to make a heat shield.

I can just about work this out for myself, but if anyone has any pics to inspire me as to the best shape to try for then feel free to show them.

Oh and does anyone know where's the cheapest place to get a couple of carb-to-manifold gaskets?

Thanks :)

Jordan Gibson

I'd be interested in that as well, my Sprite does the same yesterday actually.
I do have a diagram of a DHLA face if that would help you Jordon.
Brad (Sprite IV 1380)

Thanks Brad - I should be fine using a gasket as the face template (if that's what you were thinking of).
Jordan Gibson

I can never see the point in a heat sheild as it's simpler, neater and more effective to get a thermal barrier coating applied to the inlet manifold and say goodbye to the problem for ever.
Daniel Thirteen-Twelve

Apparently Maniflow specifically say do not coat their manifolds as it raises their temperature above design and shortens life. Or so I have read.
Jordan Gibson

ceramic coating the exhaust manifolds may help reduce some underhood temperatures. It actually prolongs the life of the manifold too because it puts a thermal barrier between the exhaust gasses and the manifold as well as between the engine bay and the manifold. Wrapping it in insulation will cause the manifold to overheat. What daniel was suggesting should be fine. We are talking intake manifolds here right? An intake manifold draws cool air into it. It doesnt heat up except by heat transferred to it from the cylinder head or through radiant heat comming off the exhaust manifold.

Regarless of what you think, coating the intake manifold would potentially reduce the temperature of the intake a few degrees. and would cause no harm to the intake manifold. I cant see how it would be bossible to cause an intake manifold to get so hot that it would "exceed the design levels and shorten it's life". In the exhaust manifold what this means is a phenominon known as thermal fatigue. To get to a state of thermal fatigue would require that your intake manifolds get cherry red hot on a regular basis. If your intake manifolds ever got THAT hot, your fuel mixture would burn up long before getting to the engine, backfire out the carbs and even cause the engine to stall.

The real downside to coating the intake manifold with jet hot or something like that is that it may make the inside bore of the manifold too smooth. The inside walls need to be just a litle rough in order for the air to flow freely into the engine and to preserve the fuel atomization. It works kinda like the dimples on a golf ball. Now if you coat the inside and make it REALLY smooth you will notice a loss in horsepower as a result. what may be better is to take some "header wrap" which is designed to be used on exhaust manifolds (but should never be used on exhaust manifolds as it promotes premature thermal fatigue) and wrap the intake manifolds with it.

That way you maintain the proper surface while still reducing the temperature a bit. What I think is equally critical is reducing the temparature of the carburettors, if your float bowls are getting really hot, it makes the fuel boil and causes vapor lock. Thats one reason why heat shilds are used. they are an all in one solution. You can even add reflective insulation to the underside of the sheild.
S.A. Jones

I was skimming and read over the word 'inlet' in Daniel's post. I was referring to the exhaust manifold, led by suggestion I'd read in the archive to wrap it to reduce vapour lock in the carb. Sorry Daniel.
Jordan Gibson

Have a look on Denis Welch motorsport website and type heat shield on the MGC cataloge. Have one on my midget and it seems to work well.

http://www.bighealey.co.uk/search.php?keyword=heat+shield&Search=Search&cat=3
brian s

Yes Inlet/Intake.

S.A. Jones post is very informative but then again he is from the USA and they do seem to be a long way ahead of the UK in the use of thermal barrier coatings.

I currently have had the exhaust manifold coated inside and outside and so will be interested to see how long it will last.

The coating on the inlet manifold made a dramatic difference to my Sprite that really suffered with fuel vaporisation.
Daniel Thirteen-Twelve

This thread was discussed on 08/03/2009

MG Midget and Sprite Technical index

This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.