How long does your 401 need to warm up for before you can drive off?

Right.
In the photos see the smaller passages in the head and the intake
(the second passage from the end at each corner of the intake. And on the head, the second passage from the end)
Those are the exhaust (heat) passages.

 

1800 RPM fast idle is much too high. It's outright dangerous, and terribly hard on the transmission. For that matter, it's making life for the distributor gear somewhat miserable trying to spin the oil pump that fast with cold oil. 1200 rpm fast idle may be about right, kicking down to under-1000 rpm when you tap the gas pedal after starting the engine. No wonder you thought you needed upgraded brakes to get down the hill by your home! I wonder if having the fast idle turned up that high is "compensation" for something else that isn't working properly.

Take a look in your service manual for confirmation on idle speeds.

 

Idle speed with the 750 cfm carb needs to be higher than the one 4gc that was something like 525 cfm. According to Edelbrock 1800 rpm for the first notch is in the ballpark and isn't readily adjustable (you have to bend the linkage). It really doesn't matter though because I kick it off of the first notch before it runs 2 or 3 seconds. That drops it down to 1100 rpm which is adjustable with a screw.
Even at 1100 rpm that's still something like 15-20 mph. My road is a 10 mph road as it is rough, narrow, and steep ray:

 

As far as I can tell there is just the one tube running to the choke housing.



It goes out from the bottom there to the manifold. I'm not sure where the filtered air pipe should be.



The piston is present and moves freely. I still haven't picked up my 0.026" wire to set it yet.



It won't go up to this fastest idle position on it's own; I have to set it by hand. Either it's not cold enough or it needs setting. This should be about 1200 rpm and go down the cam from there?

The exhaust crossover got hot much faster than the rest of the engine, although I forgot to check to see if the heat riser valve moved at all during the warm up period. Do they normally still work on old cars?

jeremy

 

Carb CFM has nothing to do with the required fast idle speed.

1. 1800 RPM for a fast idle is INSANE, even if it's "approved" by Edelbrock.
2. I don't understand why the fast idle screw doesn't adjust the fast idle speed. Turn the fast idle screw down a half-turn, see what happens.

If the fast idle on the high step was reasonable, you'd kick it off the high step after two or three seconds, just like you're doing now. You'd then have an idle speed UNDER 1000 rpm, perhaps 900 or so.

WE AGREE: Your current idle speed is too damn fast to safely drive that downhill, narrow road. Additional warm-up isn't the answer. Fix the excessive idle speed, and you're all set.

Of course. The choke housing gets only the HOT air.

If it exists--and I expect it should--it would be on the inlet side of the stove in the manifold. In other words, wherever the manifold is getting "cold" air that it heats and sends to the choke housing. There's perhaps a rusted stub of a pipe stuck in the manifold. That stub would be removed, and a formed-steel tube that probably leads to the air cleaner or to a port on the carburetor would go in it's place.

Don't overlook a paper clip.

That would likely be an adjustment of the choke coil. How far away from the "index" position has the coil been turned? If the choke coil is adjusted properly, you may need to bend the linkage to the fast idle cam so that when the choke blade is totally shut, the cam is rotated so that long stamped line aligns with the fast idle screw, as shown in your photo.

Yup.

Verify that it works. Those things were known for seizing forty years ago. If the manifold gets hot that quickly, there's a good chance that the heat riser valve is stuck closed. You'll enjoy better performance at mid-to-higher rpm if the valve was stuck closed, and you free it up so it works properly.

 

Really? 0.026 seems like such a specific measurement I though it ought to be right on. I'm walking past a guitar store on the way to the barber on Saturday, so I'll pick one up then.

It was two notches rich when I found it but it now at the index mark.

I'm going to have a look and probably take some pictures to see if I can discover where this should be.

It definitely turns freely, I did it just the other day. I'm just not sure which position it is in at which point. I take it the valve is closed when cold and opens up when warm?

jeremy

 

Can't hurt to be exact.

OK. I'm a little surprised.

Good idea.

Yes, closed cold. If you have dual exhaust with no crossover pipe in the exhaust system--like most of the original factory exhaust systems--you will see one tailpipe stop or almost stop flowing when the engine is cold.

 

I pulled the tube off and there is definitely vacuum coming from the choke housing.

 

I'm not able to find such a tube. There is only the rigid tube from the manifold to the choke housing.



I've examined the carb and intake manifold from every angle and cannot find any ports or hook ups that aren't in use.



Is there anything missing or out of place?

 

The heat riser valve definitely turns freely. I have a single exhaust.

It normally sits in this position.



As you can see the thick part is towards the back of the car. I can easily rotate it towards the front about ninety degrees like this.



I can go further but now I'm up against a spring. Sometimes it stays other times it springs back.



Today I started it and it was in the first, rearward position. Manually rotating it to the front seemed to make the heat tube from the manifold to the carb hotter as I held the valve and rotating in back to it's starting position seemed to slow the heating process, making me think that it's normally sitting open.

 

Picture #2 & picture #5 has a piece of vacuum hose that looks like it may go nowhere. This hose attaches to the tube that goes to the bottom of the manifold in the center to supply CLEAN & FRESH air to the choke tube on the rear of the manifold. As you can see the rubber hose/tube is attached to the rear top portion of the carb. which already has filtered air going into it as it had to pass through the air filter 1st.
Understand???

 

I got my wire and adjusted the choke piston linkage. It needed a bit of adjustment but not much. I tried starting the car again and it still needed five minutes before it would go in gear without stalling.

Is there anything else that could be causing this? It feels like nothing I do makes any difference.

jeremy

 

You mean the one on the right here, with the rigid ninety degree elbow?



It goes over the engine and then down to this thing.



What is this thing and what's it doing with vacuum?

jeremy

 

Or do you mean the skinny one coming out of the top of the carb? It goes to the transmission.

 

The one from the top of the carb. You can't be looking at the right/correct hose. There is NO vacuum from the hose coming from the top of the carb. If in actuality that hose was hooked to the trans. modulator line the trans. WOULD NOT SHIFT as it should. The shifts will be REALLY LATE.

 

Is this the one you mean?



It comes out the top rear of the carb and goes down into a rigid line.



The rigid line picks it up in-between the coil and distributor.



Down it goes.



To the transmission. There is a second line leading to the transmission as well, from the intake manifold. Perhaps one operates the pitch switching function?

jeremy