Interesting experience with heat riser

[Joe Flanagan]

I noticed that my Plymouth was idling rough when hot and I got to thinking maybe my heat riser wasn't functioning. I kept putting off checking it until last night when I was driving and the car really struggled and stumbled when taking off from first gear. This morning I discovered that the heat riser wasn't moving at all once the car got warm. I was able to move it with my hand and what a difference. The car idles nicely and taking off from first is as smooth as can be. It turns out that the heat riser was just stuck after sitting for so long during the rebuild. I ran the engine once every few weeks but apparently it wasn't enough. It took rotating the counterweight by hand for several minutes to really free it up so that it moves easily. Anyway, I can't believe what a big difference this makes in the driving experience.

Edited September 20, 2014 by Joe Flanagan

[55 Fargo]

Hot exhaust gases being channeled under the carb base, so super hot carb, then restricted exhaust flow= the symptoms you experienced.

The heatriser, really is a useless/problematic item some of the time....

[TodFitch]

. . . The heatriser, really is a useless/problematic item some of the time....

Perhaps if you live in a dry climate. It definitely helps on cool weather cold start drivability where I live.

[55 Fargo]

Tod yes it does help on cool weather initial start-up, but it sure don't help if stuck in the wrong position when the weather is either warm, or the engine is at operating temp.

Personally I would rather have no Heatriser, than 1 that is not functioning correctly.

So yes the engineers designed them for a purpose, but if they do not function, they can be a bit of a problem for either a) cold start initial operation, temps at or near 32f/0c especially wet conditions leading to carb icing, c) warm/hot engine operation,leading to issues as the OP has described.

Next time, will be more speciifc in my comments..

[Joe Flanagan]

I thought I had this all settled but apparently not. The counterweight moves freely now and springs back when you release it. It moves freely forward and backward with no sticking at all. But what's happening now is that the counterweight remains in the cold position at all times. It doesn't matter how long I've been driving. You can move it clockwise (toward the front of the car) and it won't stay. It just springs back to the cold position. Is it possible I have the spring in backwards? According to the manual, with the engine cold, you should be able to rotate the counterweight clockwise, toward the front of the car about 90 degrees. When you let it go it should snap back under spring pressure. My heat riser does all that, but it does it when the engine is cold AND when it's hot. Apparently it is not responding to heat. Any ideas what the trouble is?

Edited September 21, 2014 by Joe Flanagan

[Niel Hoback]

Maybe you have too many wraps on the spring.  Don't wind it around the pin, just hook the end on without wrapping it.

[Joe Flanagan]

Thanks, Niel. I'll take a look at that. I also discovered that the counterweight doesn't move when I rev the engine, which would support the idea that it's under too much spring tension. 

[Young Ed]

I believe when I did mine the directions were specific on how to wind the spring.

[Joe Flanagan]

Yes, they are specific in the manual, too. I just can't remember how I did it. Looks like I'll have to take the counterweight off and recheck everything which ought to be a lot of fun since everything is pretty tight in there. The thing that seems to be most in the way is the heater duct and I'll be damned if I'm taking that thing out. Unless, of course, I have to. 

[Don Coatney]

Can you post a photo of the spring? While rooting through my old parts box I found this spring pictured below and I do not have a clue where it came from. Zippo for sizing.

 

[wdoland]

I never knew those springs were so big!

[Don Coatney]

I never knew those springs were so big!

They come in all sizes.

 

[Joe Flanagan]

That sure looks like a heat riser spring, Don. 

[Don Coatney]

Thanks Joe.

[Joe Flanagan]

I just unhooked the spring and reattached it with the minimal possible amount of tension. The result is it still won't move from the cold position. Again, it moves freely if you move it by hand, but the spring itself, if it's expanding with the heat, won't move the counterweight. Maybe I have the spring in wrong. In any case, I can't get the counterweight off without launching a major production, so I'm going to wire it shut for the time being. With an extra set of hands, I might be able to get the counterweight off and experiment further. It's difficult getting a socket on the small bolt that attaches it to the shaft. 

And it just occurred to me: Is it possible I have the counterweight attached wrong? As in, in a position where it can't be overcome by the expanding spring? I seem to recall on my truck that the counterweight, in its cold position, had to be right near the tipping point. 

[_shel_ny]

Joe, you probably have all these pics, but just in case.

[Joe Flanagan]

Thanks a lot for posting those, Shel. It looks like I have the spring installed correctly. My counterweight might be tilted a little too far toward the back of the car, I don't know. I just drove it for a while with the heat riser fixed in the warmed-up position (so no hot air can get up into the intake). It's better, but I can't say the difference is drastic. I don't know what accounted for the big difference I felt the first time I moved the heat riser into the hot position. That was when the bushings were sticky and I could get it to stay in place by itself. The car idles better but is still a little uneven and it seems to want to stall when taking off in first. It's not really bad but it's there. I need to recheck my idle speed and mixture because I haven't done that since I got the engine running a few years ago. 

[Niel Hoback]

   It doesn't sound like the heat riser valve is your problem.  I would be looking at the float level and the accelerator pump . You describe a "too lean" situation. There's a tiny chance its timed too late also.

[Joe Flanagan]

Wouldn't a vacuum leak also create a too lean situation? 

[Niel Hoback]

YES.  Good call.

[Joe Flanagan]

So I think what I'm going to do is put a vacuum gauge on it tomorrow just to see what that tells me. I would like to try all the possibilities that do not involve taking the carburetor apart. If none of those are the fix, I'll dig into the carburetor. I will also check the timing. 

[Niel Hoback]

   Check the manifold nuts and bolts, carb base nuts, cap off the wiper connection.  Tighten the carb bowl cover screw next to the choke lever.  Spray carb cleaner, penetrating oil, starting fluid, stuff like that along the manifold while its idling and listen to the rpms. Sometimes you can hear a leak through a length of heater hose.  Mine once actually made a perfect whistling noise only when it idled, but it was as if it was saying,  "Hey stupid, I'm over here!"  

[Lloyd]

The spring should be moving the counter weight as the engine warms up. Plus the counter weight usually moves back and forth while the engine is idling unless the spring is so tight it will not allow any movement.

Perhaps the valve has separated from the shaft.

[TodFitch]

The spring should be moving the counter weight as the engine warms up. Plus the counter weight usually moves back and forth while the engine is idling unless the spring is so tight it will not allow any movement.

Perhaps the valve has separated from the shaft.

 

On my car the force of the exhaust will move the heat riser to the hot position once the RPM is high enough. You can readily see this when the engine is cold by blipping the throttle while watching the counter weight.

 

Also on my car, it has to get fully warmed up (like driving the car for more than a few miles on a warm day) before the counterweight stays in the hot position when the engine is idling.

 

Looking at it, I think it works by having the spring weaken when it gets hot. Then gravity acting on the counterweight and the flow of exhaust against the flapper valve in the manifold move the assembly to the hot position. When it cools off the spring regains its strength and pulls the flapper to the cold position against the force of gravity on the weight.

[Joe Flanagan]

At one time, the counterweight did move when revving the engine. But then I had to rebuild the engine for a second time (that's a long story) and I might have removed the counterweight, then done something wrong when I reinstalled it. But I don't remember ever taking it off. That doesn't mean I didn't. I just don't remember doing it. But now, the counterweight does not move when I rev the engine. I've confirmed that much. As I mentioned in an earlier post, I might have the weight set back a little too far toward the back of the engine and the spring can't move it. My 56 Chevy pickup has a very similar arrangement. I experimented with it when I had the manifold off. I took a hair drier and heated the spring so I could see how it worked. If the counterweight was too far back, the spring couldn't move it. It took several tries to get it in the correct position, which wound up being right near the tipping point. Once the spring started expanding, the weight would tip and between gravity and the force of the expanding spring, the valve would change position. 
Someone suggested the valve maybe got separated from the shaft. This occurred to me also and I sure hope it's not the case. I guess the only way to tell is to pull everything apart but that would be a last resort. Seems to me I can hear the valve scuffing slightly inside the manifold when I turn the counterweight so my guess is it's still attached. 

I'll report on what the vacuum gauge says later.