So i got my 51 out today and drove about 10 miles and when i came home i decided to get out the Non contact temp gauge and was taking readings from all over the engine and when i put it on the intake manifold just below the carb, it showed over 300 degrees! I checked both side and they were the same. I don't think that is how its supposed to be. Any ideas Why?

 

The heat risers on a Flathead run up through the block, into passages in the intake to prevent carb icing, and to help warm the motor. Most carbureted vehicles are like this. P.S., exhaust temps run about 1,200 degrees, so 300 in those riser passages doesn't sound abnormal, just keep the motor around 160. Flatheads forever !

 

What engine do you have?

The flat six or eight?
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The heating exhaust passages in the V8's are about the size of a penny. Hot-rodders in the '50's used to put pennies in the holes to block them, it is surprising how much it changes the exhaust note! (makes it crackle)

I tried running with SS shims over the passages, with 1/4" holes drilled in them, to reduce the amount of heating, but not eliminate it. Even in mild (70 deg) weather the engine took 5 minutes on the road to eliminate bogging, it was just too cold. I pulled the shims out after a couple weeks. Put your hand on the back of the carb after a cold start, you'll be surprised how cold it gets! I saw frost once.