C1 (1960) Choke issue

[Donald H.]

This is a dual quad setup, so it has the choke assembly with the tube out the rear edge. Also, the carbs were restored by Bob Kunz and just now getting everything up and running.

First question is regarding parts configuration. The picture below is with the plastic/bakelite cover removed. You can see the baffle. This is made of some sort of gasket type material. There was nothing else between this baffle and the outside cover. I see that the suppliers sell a gasket and have seen exploded diagram of the other type choke assembly that has a round/thin gasket between the cover and the baffle. I have not found any diagrams of the type of choke I have.

Do I need the gasket between the cover and the baffle?

Choke baffle.jpg

Now for my problem. The choke engages fine on cold start. Idle is 1,800 to 2,000 RPM. However, after the engine reaches temperature and I punch the throttle, the choke does not fully disengage. The butterfly is not vertical and the cam at the idle lever does not complete release to slow idle (sorry for the description), but here is another picture

Fast Idle cam.jpg

With the choke cover off, the arm that moves the butterfly and the piston in the choke housing all move very freely. I have read that the piston can get junked up, but mine seems to all move fine. I have tried rotating the cover to the full lean direction, but still doesn't help. It seems that the spring is not compressing enough to fully disengage the choke.

I have tested the spring off the car with a heat gun, and it seems to move enough. From cold 40 degree temperature the spring compresses 90 degrees radius at about 100 degree temperature. I guess my question is, how hot is it supposed to get at the choke area through the tube? That's the only think I haven't check, i.e. how hot it is where the tube goes into the choke at operating temperature.

I will try that next and then remove the tube and make sure the tube from the choke to the exhaust manifold is clear, and the tube inside the exhaust is also clear.

Any other suggestions?

Also, I not sure what the small piston in the choke really does?

[Timothy B.]

Re: C1 (1960) Choke issue

Donald,

If Bob Kunz overhauled the carburetor I am sure the hot air choke adjustments are correct.

The hot air choke assembly is attached to the carburetor and there is a small vacuum hole that pulls a vacuum against the choke vacuum break piston. When everything is adjusted correctly, the pull of the vacuum against and through the sides of the piston balances against the choke coil spring and allows the choke to partially open and as the engine warms and the spring expands the vacuum opens the choke full. When the choke coil spring cools, the butterfly closes depending on how much the spring contracts.

Vacuum also pulls through slots in sides of the piston creating a vacuum through the choke coil and pulls the heated air from the attached tube that goes to the exhaust manifold. The bottom of the exhaust manifold should have another tube that attaches to the carburetor air horn this allows the vacuum to pull filtered air through the tube and exhaust manifold up through the top tube and into the hot air choke assembly.

In order for all to work properly separate adjustments are made to the choke coil, vacuum break piston and fast idle cam position, hopefully you only turned the choke coil. Make sure the coil spring is capturing the lever correctly, the best way to adjust the coil is a 68* the coil should be moved to the rich side enough to fully close the butterfly. If you have a service manual it's best to read and understand how all this works.

[Donald H.]

Re: C1 (1960) Choke issue

I have the ST-12 which references to 61 Chevrolet manual, which I also have. The problem I am having is that all the adjustments are for the choke with the heat tube coming out of the center of the housing. It references adjusting the intermediate choke rod which the dual carb setup does not have. The piston and housing is much different, and there is no intermediate choke rod to adjust. I'll keep reading to see if I can get anything from it.

Thanks,

Don

[Dennis C.]

Re: C1 (1960) Choke issue

Don,

There might be more information in the Chevy passenger car shop manual. I am not near mine to check.

Dennis

[Donald H.]

Re: C1 (1960) Choke issue

Don,

There might be more information in the Chevy passenger car shop manual. I am not near mine to check.

Dennis

Really isn't much in the ST-12. And per my post #3 above, there is so much difference in the two chokes that the info in the 61 Passenger Car Manual doesn't make sense to me. But I will keep reading to see if I can figure it out.

Thanks,

Don

[Joe M.]

Re: C1 (1960) Choke issue

Donald, I have the same problem with my single carb set up. I honed the inside of the piston chamber and everything appears to move freely, but when I tap the gas pedal, it will not drop to the proper idle. I will be interested in finding out if someone has a solution to this problem. It is a problem that is way over my head; so I have been living with it for years.

[Gordon W.]

Re: C1 (1960) Choke issue

Donald, I have the same problem with my single carb set up. I honed the inside of the piston chamber and everything appears to move freely, but when I tap the gas pedal, it will not drop to the proper idle. I will be interested in finding out if someone has a solution to this problem. It is a problem that is way over my head; so I have been living with it for years.

When the engine is warm can you turn the Bakelite choke cover a tad further and see the choke fully open?
i had a similar problem and instead of setting the choke when cold I set it when hot so that the choke was fully open and my problem was solved.

[Dennis C.]

Re: C1 (1960) Choke issue

Don,

i would suggest you call the restorer of your carbs and ask his opinion of your problem.

Dennis

[Donald H.]

Re: C1 (1960) Choke issue

Thanks all,

i did try turning the cover with the engine warn, but may not have turned it enough. The book says that the mark on the cover normally lines up with the center mark on the housing. Mine is way to the right (lean).

bob Kunz did the restoration so I am confident that the carbs are set up correctly. I'm going to take the tube off and make sure there is not any blockage.

Don

[Pat H.]

Re: C1 (1960) Choke issue

Check the spring in the bakelite housing. The current reproductions they sell are for later AFB and not WCFB's. I bought one from Paragon and it wasn't right for the carb. I finally found a decent one at a swap meet. That's why the mark doesn't line up

[Stuart F.]

Re: C1 (1960) Choke issue

Believe there is a manual method for setting the choke based on ambient temperatures, but I don't have it handy (been mostly bedridden for the last number of weeks). When you arrive at a good setting which provides full closure when cold, and full open when rearly warm, then you can file a little notch in the baklite to "re-index' it. May not be best for judging though.

As for the housings; the're still out there at swap meets, but not many folks will "part out" a good and correct model AFB that can be restored. I have one myself, but want to keep it with the carburetor which I too use for parts (top plate used on my correctly dated 3461S), but intend to use it as an experimental unit some day when I can get back in my garage (already bored the primary venturis).

Hope this answers a previous PM sent to me by perhaps you that I printed and then misplaced.


Stu Fox

Stu Fox

[Donald H.]

Re: C1 (1960) Choke issue

Thanks all, I think I have it working now.