Type 3 heat riser butterfly?

I changed out the exhaust system on my type 3 square on Sunday as it was falling apart, and put in a EMPI single muffler extractor with J tubes. (Even in July I couldn't convince myself I needed heating in Brisbane)

First of all, what a ##### of a job getting the original muffler and heat exchangers off! I'm used to working on stale-air 36 and 40HPs, so the room around a fresh-air type 3 system was a bit less than I'm used to.

However my question is this: it's a single-carb early motor, and on the drivers side heat-riser tube there was a spacer piece with a butterfly valve a bit like a choke butterfly. It had a drive shaft (not connected to anything). Presumably used to regulate heating to the inlet manifold, but why and why only one side?

Idle curiosity really, as although I've kept the heat exchangers I doubt they'll go back on.

Cheers

Angus

It would have had a bi-metalic spring on the shaft like you find on a carby(automatic choke). Its only on one side as it goes from a high pressure area(#2 exhaust port) through the butterfly, then heats the inlet manifold and ends up porting into the muffler(low pressure). As the engine bay temperatue rises the butterfly closes.

Thanks for that, although I can't imagine it worked very well - even before it was blocked up with gunk.

Angus