Lean/rich mix on carb

Aug 04, 2004 5 Replies

Does the leaness of the mix on a carb have an effect on the running temperature of an engine. I had my 1600 crossflow in my kit car serviced at the weekend and they played with the mixture. I then noticed that the engine was running warmer than before.



They also welded up a hole on the exhaust manifold.



Cheers Dave


The message from "dht" contains these words:

Yes. Lean mixtures usually run hotter.

How does that work, as I have no idea. I assumed incorrectly that richer (to a point) would mean hotter as there is more fuel to burn and I guess more energy produced wich causes more heat.

Can someone explain.

Cheers D

The message from "dht" contains these words:

Damned if I can remember!

I think it's because there's more air (and therefore oxygen) in a given volume of mixture - a hotter flame will result. Oxyacetylene welding experts may concur with this. Anyone?

Flame temperature increases as you go leaner up until stoichiometric (14.7:1 air/fuel ratio) and then decreases again as you go weaker than this. Richer than stoich runs cooler due to the excess fuel and weaker than stoich run cooler because there's less mixture burning per cycle. However an idle fuel mixture adjustment shouldn't affect anything at higher rpm or general running so probably isn't the cause of overheating.

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