59 Pontiac choke problem

[dl456]

Hello,

59 Pontiac 389 with Rochester 2GC carb. Will not pull heat to the choke housing from the stove pipe. Has good vacuum at the housing , coil spring is tested and good, crossover is plenty hot.

I do notice a screw in the edge of the intake manifold that threads into the side of the hole where the stove pipe goes.

Could this be a vacuum jet of some sort or simply a plug.Thanks for any help.

Dennis

Choke is set two notches lean and does not fully open when warm.

Edited September 21, 2022 by dl456 (see edit history)

[carbking]

Have you checked the heat tube to be certain it is not clogged with rust?

 

Jon

[dl456]

Jon,

It was clogged. I caught that during the rebuild and it is clean.

Thanks,

Dennis

Also cleaned and vacuumed the hole in the intake

Edited September 22, 2022 by dl456
Added info (see edit history)

[Bloo]

If you have verified that the port on the choke draws air, the choke stove must be plugged up. There really isn't anything else.

[Oldtech]

Not sure the position of the screw that you mentioned but the pipe to the choke must be open to draw air into the choke stove.  How hot is the stove on the carb? maybe bimetal spring is not working.

[dl456]

The port at the choke has good vacuum and the stove pipe is perfectly clean.

Oldtech,

I also question how this pulls hot air with vacuum. The hole for the stove pipe in the manifold is a blind hole.

The screw(plug) comes in from the side at a right angle to the hole. If the hole was open on the bottom it would pull exhaust gasses from the crossover.

Never had this issue and have never noticed the screw in the intake before.

Thermostatic spring is tested and working fine,just not getting heat.

Edited September 22, 2022 by dl456 (see edit history)

[Bloo]

This cannot be right. A choke stove has to have an air inlet. Air flows through it getting heated. This is clean air, not exhaust. Maybe post pictures?

 

 

Edited September 22, 2022 by Bloo (see edit history)

[dl456]

Bloo,

I agree. I suppose it’s possible that the screw in the side of the intake has been installed at some time but it does not appear to be added. If removed,it would provide an inlet. I suppose it could have a hole in it to provide a “jet” for vacuum,

To remove and investigate I will have to remove the valve cover and likely the intake.

Thanks

Dennis

[Bloo]

They don't typically have a jet. The restriction that meters airflow is in the choke housing or the carburetor. By the 1970s they were usually using filtered air, usually from the main air filter, but in the 1950s, probably just an inverted "U" of tubing to keep crap from falling in. It is very important that it not be allowed to suck exhaust, only hot air. See if you can find pictures of another engine like yours on google images. It might solve a lot of mysteries.

[carbking]

The early Pontiac tripower intakes had a single tube from the choke to a heat stove in the heat crossover in the intake. The tube was simply pressed into the intake. There was a plug on the side of the heat crossover that plugged an access hole. There was a steel tube also connecting to the intake heat stove that passed completely through the exhaust crossover to the driver's side, and it was open on the drivers side. This tube was maybe 10 inches long from memory. Inside the tube was a piece of twisted flat steel that slowed the air flow through the tube.

 

So: unfiltered air entered the tube on the drivers side of the heat crossover, was heated as it passed through the tube in the exhaust, entered the heat stove (integral in the casting on the passenger side) and then was pulled via vacuum through the tube from the manifold to the carburetor choke housing.

 

Somewhere around 1961 or so, the single choke tube was changed to two tubes: one from the air intake of the carburetor to supply FILTERED air, and the other connecting to the choke housing. Both were connected to a bracket with a U-tube that was inserted into the heat crossover, sealed with an asbestos gasket, and secured with either one or two screws, depending on year. The long tube going from side to side was eliminated.

 

Jon

[dl456]

Thanks guys,

Screw refuses to be removed at this point. Still no heat.

Is it possible that the two barrel intake has a system similar to the tri-power?

I’ve never seen a plug in the side of the heat crossover in the intake and this is the screw that refuses to come out.

If it has a tube that runs to the drivers side of the intake, I may find obstruction there.

currently it acts as a blind hole.

Thanks again,

Dennis

[Frank DuVal]

No flow = no heat to choke coil. Find the path and open it. Do you see a hole in the choke stove that could lead to air? Either that screw needs to be removed, or it is the red herring and the hole is not what the screw is in. Scrape around inside the stove housing.

[carbking]

You may have to remove the manifold and apply heat to remove the screw.

 

If you do not wish to do that, here is a "work-around":  Heat stove fabrication

 

Jon

[dl456]

Thanks for all the comments and suggestions.

I’m still baffled by this issue.

At 4 notches lean the car starts quickly and the choke will completely open in about 4 minutes. Still very little heat at the top of the stove pipe.

I will live with this until winter and pull the intake.

There is a simple solution and we will figure it out.

Will report back.

Thanks again 

Dennis