Heat riser in a '64 Dodge Dart

Just bought a new old Dart. It is having issues when taking off. If it warms up for 10 minutes or more it seems pretty good, but is still very sensitive when taking off. I have to lightly feather the gas pedal or the engine cuts out on me. The guy I got it from said he went through carburator adjustments and it didn’t help, and that maybe it was the heat riser. Any thoughts about it?

What engine do you have in the Dart? Some engines of that vintage had a heat riser valve that directed exhaust gasses through a passage in the intake manifold. This heated up the manifold to insure vaporization of the fuel in cold weather. The heat risers I recall were operated by a bimettallic spring that opened it on cold temperatures. There is a good chance that yours does not work since they tend to jam or rust to pieces after a few years.

Also check if you have a hot air inlet for the air cleaner. I have seen them cause similar problems.

The engine is a slant six, the 170. How to go about checking if it is the spring? I’m not too sure where to find the heat riser.

It sounds like a faulty or misadjusted accelerator pump. Has anyone checked it? Look down the carb with the engine off and move the throttle by hand. You should be able to see a squirt of gas as you open the throttle.

The heat riser is located below the carburetor. Look where the intake manifold is bolted to the exhaust manifold before they branch off to the cylinders. Most of the valve is inside, but you should be able to see a coiled up spring attached to a rotating shaft with a small counter weight. You may need to stand on you head in the engine compartment to see it.

I forgot to mention that a basic check of the riser is to rotate the counterweight on the shaft and see if the spring returns it to it’s original position. It is only supposed to rotate about 90 degrees.

My Dodge Dart was a 273 V8, but it also had a hear riser. When these things get stuck open, they keep directing hot exhaust gasses against the intake manifold, thus leaning out the mixture. This makes the car stall and idle irregularly. Mine had to be constantly freed up; there was aspecial spray to get rid of the rust and deposits. A worst case scenario is if the thing is installed backwards; then it is always heating up the incoming mixture.

Best find an older mechanic who has worked on cras with heat risers.

Good luck!

This sounds exactly like the 6-cylinder '63 Plymouth that my father bought in…1963. And, everyone else whom we knew with 6-cylinder Chrysler products back in those days used to report the exact same symptoms.

Based on what the wacky service manager at the dealership said, as well as what every independent mechanic to whom we brought the car also said, we finally concluded that the automatic choke on that era 6-cylinder Chrysler products just did not work very well. The only solution was to allow the car to warm up for at least 15 minutes before driving it on a cold morning. Other than that quirk, it was a very reliable car.

Hmmm, the heat risers on my Dodge and Pontiac of that vintage were in the passenger side exhaust manifold. Spray a lot of penetrating oil and bang on it to free it up, but might be better off putting in a manual choke and be done with it. Never heard of a heat riser being on the intake manifold.

The float level could be low. Some accelerator pumps had a slot near the top of the well where the gasoline passed through. If the fuel level is too low, no gasoline gets to the accelerator pump. At the exhaust manifold to the air cleaner housing, there should be some kind of large tube for the choke stove. Without hot air going to the intake, some engines will stall when you step on the gas. A broken carb gasket could have that effect too. Vacuum advance could be shot. You may have too many vacuum hose leaks. PCV or advance. There weren’t many hoses in those days.

I put a manual choke on a 225 slant six one time. In retrospect, it might have been better to try to get the system working the way it was designed to.

The heat riser is a heat actuated butterfly valve that sits in the neck of the manifold. The shaft has a bi-metallic spiral spring and circular damping weight attached on one end and an an anti rattle spring on the other end.

When the engine is cold the spring is at it’s shortest and closes the butterfly restricting the exhaust manifold, the hot exhaust gases are directed by the obstruction into a heat tunnel that passes under the carb to heat the fuel air mixture.

As the spiral spring heats up it pushes the butterfly open and allows more exhaust gases to flow through the downpipe and into the exhaust, a stop pin is pressed into the manifold to stop the butterfly at the fully open position.

Like most exhaust parts, heat risers rust. and both the stop pin and spring lever pins wear rapidly if not maintained. Easiest check is try to rutn the damper disk, if it’s siezed you can try penetrating fluid to free it up, the shaft is bushed and might free up. More likely is the spring is shot or the pin is worn away. If you can swing the damper with no resistance at all, this is the problem.

Repair kits are available, but the butterfly is welded to the shaft and has to be carefully ground free. The new bushes have to be reamed and there is a setup procedure to set the spring and shaft position with the butterfly before welding the new butterfly to the shaft. I’ve just done one on my 73 New Yorker, not my favourite job.

The 6 pot manifold is shown here (though a different year) you can see the heat riser in the manifold nexk.


Good luck.

You don’t have it on the intake of a V8 but on the six, the intakes were stacked with the exhaust manifold right under the intake. I think this engine had them bolted together at the carb base right below the carburetor so it looked as if the heat riser valve was attached to the intake. Close to it anyway. I hated tuning that type of engine because the distributor was under the slant and was usually dirty and greasy. Memories best forgotten until these new nightmares were created.