'64 choke problems

[Dad]

Time to get the '64 out and ready to go. Tried to start it and no go, opened the hood and removed the breather and set the choke. That's the reason I'm posting this. The piston in the choke stove was frozen up again with carbon/black soot. After I set the coke it started right up.

By the way it is stored with no fuel additive or battery charger. All I have ever tried to control while storing a car is moisture and mice. I did
start it and take if for a drive sometime in November on a nice day.

I've had the choke apart a dozen times, even blocked the runners in
the manifold. Also took the right side manifold off and bored out the
stainless steel heat tube and replaced that. Old one was ok but
changed it anyhow. New hose and heat tube to the choke bimetal spring
housing. Polished the brass piston and honed the pot metal bore in the
housing. Put it back together and it works fine for about 100 miles
and then it locks up from soot. The way I see this thing working is to
suck fresh air from the top of the carb down through the exhaust
manifold to heat it for the bimetal spring to release the choke at
running temperature.

Somewhere in the world of one Carter WCFB gasket fits all, there must
be a port that is being left open or closed that is running exhaust
soot into the choke housing and I'm at a loss to know how to ask for
or get the right one if that is the problem. That is if there really is one that is correct. Tried three or four so far which all are about the same and it still plugs up way to fast.

Then again is it the way our new fuels burn? I've never seen this much
soot in an engine before. Any first hand experience that might help
would be appreciated.

 

[vetzs]

I could be wrong but I believe your choke tube (carb to manifold) has bruned through and is allowing soot into the choke housing. It could also be that someone has installed standard tubing. I believe the choke tube is meant to be blocked off inside the manifold.

 

[Dad]

I could be wrong but I believe your choke tube (carb to manifold) has bruned through and is allowing soot into the choke housing. It could also be that someone has installed standard tubing. I believe the choke tube is meant to be blocked off inside the manifold.

Not sure I follow your thinking, as I said I've had the choke apart a dozen times, even blocked the runners in the manifold. Also took the right side manifold off and bored out the stainless steel heat tube and replaced that. Old one was ok but changed it anyhow. New hose and heat tube to the choke bimetal spring housing.

 

[vetzs]

Getting soot in the choke houseing in my mind can only come from the tube inside the manifold being open allowing soot to travel up the choke tube to the choke housing.

I suspect the tube that you drilled out of the manifold and replaced is open and not sealed as it should be. Then when the tube from carb is inserted it sucks soot.

I assume that when you say you replaced the heat tube parts you got replacements from a vendor rather then making them up yourself. If that is the case, my theory as to your problem would not apply.

I would like to know the final outcome on your problem and it's cure.

 

[67l36driver]

Getting soot in the choke houseing in my mind can only come from the tube inside the manifold being open allowing soot to travel up the choke tube to the choke housing.

I suspect the tube that you drilled out of the manifold and replaced is open and not sealed as it should be. Then when the tube from carb is inserted it sucks soot.

I assume that when you say you replaced the heat tube parts you got replacements from a vendor rather then making them up yourself. If that is the case, my theory as to your problem would not apply.

I would like to know the final outcome on your problem and it's cure.

Yup, That tube goes thru the manifold and is there to provide hot, clean air to the choke coil.

It is sucking sooty exhaust gasses at present.

 

[JohnZ]

There's a constant vacuum draw through the choke housing to keep the heated air moving through the heat tube circuit, and the air on the intake side is drawn from the clean side of the air cleaner element. If you have that kind of soot buildup in the choke housing, somehow exhaust gases are getting into the tube that runs through the exhaust manifold - there's no other way exhaust gases can get into the choke housing.

 

[Dad]

There's a constant vacuum draw through the choke housing to keep the heated air moving through the heat tube circuit, and the air on the intake side is drawn from the clean side of the air cleaner element. If you have that kind of soot buildup in the choke housing, somehow exhaust gases are getting into the tube that runs through the exhaust manifold - there's no other way exhaust gases can get into the choke housing.

Not sure I follow your thinking either, as I said I've had the choke apart a dozen times, even blocked the runners in the manifold. Also took the right side manifold off and bored out the stainless steel heat tube and replaced that. Old one was ok but changed it anyhow. New hose and heat tube to the choke bimetal spring housing.

I drew a vacuum on the new tube in the exhaust manifold and it held, the tube from under the exhaust manifold to the choke is new and holds a vacuum. Didn't do that with the tube from the top of the carb to the one in the manifold but then it has nowhere to draw soot from.

As I said when I ask the question the tube has a known path to work in and it is getting soot in the choke piston. I have checked all the reasons for soot you have guessed at and they are correct, if it had been that simple I would have had it fixed already. Since they are correct I ask here to see if anyone else has had first hand experience in that area, my guess is now that it is beyond the knowledge here.

Thanks anyway, I’ll keep looking and let you know when and if I do find the problem.

 

[Tom Bryant]

Hi David,

So both upper and lower choke tubes are new and you have vacuum checked them for leaks so no carbon is entering through tubes from the exhaust manifold. You have also blocked off the heat riser passages to the intake manifold from the heads so no carbon can possibly enter the carb from below. Vacuum has no choice then but to be drawn into the bottom of the lower choke tube that is open to atmosphere.

The only place around the bottom of the tube to get any carbon would be:

1) an exhaust leak at the exhaust pipe packing.

2) the lower end of the choke tube is loose in the manifold allowing exhaust to blow out around the tube and be sucked back in through the choke tube.

Other than that your car must be possessed. We should get Cliff and Craig together for lunch Monday and do an exorcism.

Tom

 

[Dad]

Fixed?

Thinking that if Tom was going to do an exorcism on my ’64 I needed to get to work and figure out what was wrong. After some more thought on why the choke was seized up again and the guesses I read on here I decided to tear it down again and retest everything. Each part I removed I cleaned with cotton swabs and pipe cleaners to see where the most soot was traveling to and from where it came.

Although there was some soot in the tube I wasn’t sure if that was left over from the other times that I had just cleaned the piston and bimetal spring housing. None, or very little was inside the housing, that’s different. My guess now is that the soot that had plugged things up came for breaking loose the 40 years of crap in the tubes and manifolds. Tried to move the piston and it wouldn’t budge. Removed the housing and took it to the bench to clean it and check it out closer. Finely popped the piston out and it was clean.

While doing close inspection I remember a Chevy guy telling me that the housing sometimes warp. He is also the same one that told me the tube in the manifold was bad 2 years ago. Sure enough the brass piston was galled on opposite sides. Miked round and so it has to be the housing. Borrowed a telescoping bore gage and the housing checked round. While puzzling over that I noticed the seal on the face was not quite flat. Pushed it back in and it was still not flat, being so small I didn’t think it mattered.

Reason told me to mount the housing and recheck the bore, sure enough it was now out of round and smaller in one place than the .490 diameter piston. Removed it and checked the mounting face and there was the problem. Flat filed it until all three screw holes and the port were flat but still had some raw die cast surface in the middle. I didn’t sweep the face to see how much it bowed but the bore now checked round when mounted.

Also did a pressure test on the bore and the freeze plug leaked like a sieve. One correction at a time if I ever want to know which one corrected the problem. After everything was put back together the choke set, backed off of high idle in steps and ran fine. Time will tell if the first correction was enough.