what does this do and do I need it?

[dmtinker]

I have a 1967 250S. While I had the carbs off for a conversion, I noticed the manifold on which they sit have 2 rotating cylinders on them with what looks like a temperature operated coil. I'll post a picture tomorrow. But does anyone know what they are, what they do and how critical they are? I ask because the one that is toward the firewall has a coiled spring which is broken....

So, anyone have clue?

[Mike D]

Manifold heat risers. They were meant to transfer heat from the exhaust manifold by induction to warm the intake flow when the air temperature is cold. Mainly they serve to warp the carb bases by sticking open and cooking the manifold.

Most people weld or secure them in the closed position to prevent this event. They can be repaired but why? Seal them shut and live with the slower warm-ups on cold mornings.

[nhdoc]

I have found that you can put a medium sized binder clip on the pin under the weight which will keep the weight up and the riser closed. It's not permanent like welding but works fine. That way, if you had a reason you want the risers to work again you can simply remove them as I have now that the weather has cooled and I can use a little heat.

FWIW I removed the springs as they serve to hold the risers in the "heat" position until the manifold is hot, and sometimes beyond that. I think they are most responsible for overheating the carbs. Without the springs the weights will counter the flow of exhaust to put the risers to the "cool" or "closed" position more easily and right from the start, which is fine, it provides some heat during initial warm-up and none once you are under way. The risers only open then at idle from there on out.