MG Car Repair: 79 MGB Stromberg carb, vacuum leak, infrared themometer

Question
QUESTION: How hot should this carb be to the touch after engine warm up and 1/2 hour ride or so in 90 degree heat in light traffic? Recently, mine was hot enough after warming car up that I couldn't touch the top but for an instant. I found/fixed a vacuum leak and the carb doesn't seem to be as hot. A friend had an infrared themometer and got 160 degrees at hottest before vacuum fix. The cat converter is not red hot and the cooling system and fans are fine. Prior to the vacuum leak spark plugs one and two showed slightly lean and plugs for 3 and 4 showed rich. Vacuum before leak fixed was 15 inches and 28 inches after fix. The car seems to be running very nicely. Is the carb temperature a concern?

ANSWER: Hi Mark,
A vacuum leak makes an engine lean on mixture and a lean mixture causes an engine to over heat the combustion chamber and that can cause everything to get hotter. Why it effected 1 and 2 and not 3 and 4 means something else may be also wrong. The 79 B only has one Stromberg here in the US. Unless the vacuum leak you found was close to 1 and 2 and someone trying to smooth out the lean running engine richened up the carb mixture and the vacuum leak was mainly effecting only 1 and 2 cylinders and the over rich mixture of the carb was effecting 3 and 4.
Howard

---------- FOLLOW-UP ----------

QUESTION: Howard,

Thanks very much for your quick response.

This is my most immediate concern: Can you give me an idea of how hot the carb should be running with the car warmed up and if this is a safety concern if it's extremely hot on top to the touch? At it's hottest, I'd say it was about equal to the water temp of the hose feeding the water/auto choke (the choke does have the black heat insulator installed).

I'll see what happens to the plugs now after I've stopped the vacuum leak, which was on top of the inlet manifold at the right angle tube seat that connects to the gulp valve.

Thanks again.

Answer
Mark, I've never measured the temperature of a carburetor but I would guess they get almost as hot as everything else under the hood. It is a problem on some cars as some manufactures have taken steps to cool them down a little with a well made heat shield between the carb and the exhaust manifold and some fresh air ducted from the front. Some cars had electric radiator fans stay on after you shut the engine down so as to cool the engine down and keep an air flow across the carburetor.
Howard