1957, carbon build up in Holley choke housing

[vernz]

I have some problems with carbon buildup inside the choke housing on my Holley 4 barrel carburetor. I replaced the carburetor two years ago with a rebuilt original. At the time I did not realize I was having this carbon buildup issue. Right now my current choke pull off piston is frozen in its bore due to the carbon buildup (in full open position). I pulled my old carburetor choke housing apart to see what that one looked like and that piston is completely frozen as well with no solvents, cleaners, or oils doing anything to release it. My current carburetor choke piston was free in the fall, but not now. I'm guessing that I must be burning some oil (not visible when driving) which must be the source of the carbon. Are there any suggestions on what I can do about loosening up the frozen piston and preventing future problems like this? Is retrofitting the Holley with an electric choke an answer? Thanks, Vern

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[cokefirst]

Your heat tube in the intake manifold needs to be replaced. It is a simple job once you take off the intake manifold. You will need the following part numbers, available from most parts suppliers. The tube is B6A 9890-A it is about 7" long and mounts in the exhaust crossover section of the intake manifold. The other part you need is the deflector which goes into the where it terminated on the left side of the intake manifold, opposite from the side from the choke. You can probably get the rest of the parts cleaned up to be reused. Disconnect the tube and fitting from the choke housing as continued use may damage the choke housing. You can hook everything back up once you get the tube in the manifold replaced.

They do make a removal tool, but I find it unnecessary. A punch and a hammer with some light tapping will remove the tube from the manifold. I have replaced several of these and have never had a problem removing them from the manifold. A simple tap with the hammer will install the new tube.

I hope this helps.

 

[Ward 57]

Your heat tube in the intake manifold needs to be replaced. It is a simple job once you take off the intake manifold. You will need the following part numbers, available from most parts suppliers. The tube is B6A 9890-A it is about 7" long and mounts in the exhaust crossover section of the intake manifold. The other part you need is the deflector which goes into the where it terminated on the left side of the intake manifold, opposite from the side from the choke. You can probably get the rest of the parts cleaned up to be reused. Disconnect the tube and fitting from the choke housing as continued use may damage the choke housing. You can hook everything back up once you get the tube in the manifold replaced.

They do make a removal tool, but I find it unnecessary. A punch and a hammer with some light tapping will remove the tube from the manifold. I have replaced several of these and have never had a problem removing them from the manifold. A simple tap with the hammer will install the new tube.

I hope this helps.

This is sound advice. The generic number that all the suppliers use instead of the engineering number for the choke heat tube is # 9890 and is a stainless steel replacement. The mushroom shaped deflector on the passenger side is # 9492.

 

[cokefirst]

Ward 57 is correct except that is not the engineering number but the basic number. It is the prefix and suffix that identified a particular application.. An example is the carburetor. The part number for any Ford carburetor is 9510 but one for a Model A is not the same as one for a Thunderbird. The prefix and suffix will identify the particular part for your year make and model.

 

[jimntempe]

I have some problems with carbon buildup inside the choke housing on my Holley 4 barrel carburetor. I replaced the carburetor two years ago with a rebuilt original. At the time I did not realize I was having this carbon buildup issue. Right now my current choke pull off piston is frozen in its bore due to the carbon buildup (in full open position). I pulled my old carburetor choke housing apart to see what that one looked like and that piston is completely frozen as well with no solvents, cleaners, or oils doing anything to release it. My current carburetor choke piston was free in the fall, but not now. I'm guessing that I must be burning some oil (not visible when driving) which must be the source of the carbon. Are there any suggestions on what I can do about loosening up the frozen piston and preventing future problems like this? Is retrofitting the Holley with an electric choke an answer? Thanks, Vern

As long as you stick with the OEM heat tube system I think you will have that problem, perhaps not as bad with all new parts but years ago when I was driving cars of this era as regular "new" cars this was a very common problem, seems to be the nature of the system. If you are ok with the loss of originality switching to an electric choke heater will take care of the issue. You'll still need to free up the piston so you have a working choke pull-off.

 

[vernz]

Thank you for the responses! Here is a picture of my heat tube assembly. What is the mechanism that results in carbon deposits in the choke housing? I would think that, if anything, the choke tube is clogged with carbon and that would prevent carbon from making it into the housing. Obviously I'm wrong. I'll get a new choke assembly if I can't free up the piston and also replace the choke tube. Thanks again! Vern

 

[Ward 57]

The exhaust is routed up through the intake manifold to heat it up and help vaporize the fuel mixture going to the cylinders. That's why the intake manifold gets dark from baking the paint.
The heat tube runs through that exhaust flow and when rotted or broken it sucks that raw exhaust into the choke housing instead of clean air.

 

[cokefirst]

That tube bring warm air up from the tube in the manifold through a light suction in the carburetor and heats the coil which opens the choke plate. The tube we are talking about is inside the manifold. To repair the system, you will need to remove the intake manifold. Once it is off, you remove what is left of the old tube in the manifold, then install the new one. You can also replace the little button that attaches to the tube on the other side as it keeps debris from being sucked up into the tube and into the choke housing. if you replace the tube in the manifold it will likely be good for 20-30 years or more depending on how much you drive the car. You can put an electric choke, different carburetor, fuel injection or any of the other modifications that may be suggested. It is YOUR car and you should do what makes you happy. I prefer to keep the original system because it is reliable but nothing was designed to last 60 years. you can fix the problem by retaining the original system or you can do any modifications you like. Do not let anyone tell you that what you are doing is wrong.

 

[doug7740]

https://www.Thunderbirdforum.com/**********/preventing-paint-burn-off-on-the-intake-manifold/

Gasket Set - Intake Manifold - 1 Per car-classictbird.com

Metal reinforced at the center - designed to extend life where exhaust gases pass through heat tube.

www.classictbird.com

doug7740
1955 Thunderbird Blue

 

[vernz]

Thanks cokefirst and everyone else. Now I understand what heat tube we are talking about. I want to keep the car close to original so I guess It is time to remove the intake manifold. Vern

 

[Ward 57]

Thanks cokefirst and everyone else. Now I understand what heat tube we are talking about. I want to keep the car close to original so I guess It is time to remove the intake manifold. Vern

Have fun. At least it's not as involved as replacing a head gasket. Hope you can save the choke housing. I've got mine working great as original but if you have to go electric so be it.