I have a stock 1972 with base engine and the previous owner disconnected the heat riser by removing the curved end of the bimetal spring and leaving it hanging down due to the weight on it. He told me he did it because it was making the car run rich on startup. Well, it was running way rich on choke anyway and I discovered it was because the choke pull off wasn't functioning. I corrected that, it doesn't run rich, and am now looking at how the heat riser should be connected, but cant find any information.
As installed, the weight on the heat riser is oriented hanging downward (open I assume) and will swing upward by hand. When it swings it is facing the front of the car. In other words it swings up parallel to the side of the exhaust manifold. If I rotate the spring to make it looser and connect it to the post on the riser, the valve is down in the open position and would be open when cold. If I rotate the spring to make it tighter and connect it, then the weight of the riser rotates all the way up and over to face the rear of the car, meaning (I think) that it would be mostly closed since the weight is almost horizontal. So this seems right and would mean that as the spring heats and expands it would push the weight up to vertical (which would be open). I guess my question (or concern) is will the spring push it past the vertical point, and is there enough combination of spring and weight to allow the weight to fall all the way down to ensure that it is fully open. Is this correct? I would not want it to close when hot. Thanks for any help/comments!

 

This is the only photo of the heat riser that I have. The weight is to the rear and up, if that answers your question.





Donnie

 

The heat riser should be oriented so that the weight points towards the passenger side fender.

With the spring attached, the weight will be up (kind of parallel with the floor/pointing towards the inner fender.)

When the spring heats up, it only allows the weight to move when the engine is under load. It will not open/point down on it's own. In fact, with the engine completely warmed up, sitting in your driveway, you could rev the engine to redline and the heat riser may not even move because there's no load on the engine.

Unless you live or drive in a cold location, there's really no need for the heat riser. All it does is speed up the heating process for the manifold/carb and to get the choke to open sooner, but by default it also forces most of the exhaust gases out the single drivers side exhaust pipe.

While I have my heat riser installed, I have it wired to the open position all of the time. It just takes a few extra minutes for the choke to warm up enough to open. In Texas, not so much of a problem.

 

Hi L,
If you decide to install the heat riser and have it function you need to orient it as Donnie and Revi indicate but be careful when installing the spark plug heat shield and radio shielding so the motion of the counterweight isn't blocked.
Regards,
Alan