In response to an inquiry on another post;


Anybody messed with choke spring heaters on a six-pack set up? The Edelbrock heads I used on my project don’t have passages for heat crossover to the intake manifold creating a situation of insufficient heat at the choke well (choke never comes off completely). Even with passages through the heads the fact that I’m running headers and not the factory exhaust manifolds with a heat riser flap would create a colder than factory intake. Only way to have a functional automatic choke and have it come off completely is to heat it electrically. The 74’ motor, I picked up while back for its block, had a heated divorced choke set up for the Thermoquad(sp). I mated this heater with the holley choke spring and installed a choke heater timer/control unit from a late 70s Chrysler. The timer/control basically provides the 1.6 amps of current the heater pulls for about 6 minutes on a cold motor and then dropping down to about .5 amps necessary to keep the choke completely open through warm running.


Update 2/05/2009, since I originally posted this over on the roadrunnernest.com last year I went through two deferent NOS choke heater controls. Both appeared to have failed due to burned internal contacts. I recall when I worked on these cars back in the day; they didn’t last long when the cars were new. I built my own control based on a Bosch relay and a solid state timer circuit. It is holding up much better as of now.

I don,t have a 6 pack or live up north but thats a clean setup with e-heads.

that would work on my rr. the heat passages are blocked off. could i get more info on this.

thanks clem

More info?
These cars/engines were built originally to be daily drivers and were set-up to have decent cold running drivability from cold start up and on thru complete warm-up. Putting a thermostatically controlled heat riser valve in the passenger exhaust manifold to divert exhaust heat under the intake manifold improved cold running drivability and allowed for a divorced type choke system. As we all know, a colder denser air fuel mixture for a warm motor improves performance in most cases. Blocking the heat to the intake may help performance but it completely changes the way the original choke functions. The correct choke function is dependent on the tension created by a bi-metal coil spring. The choke spring is mounted in the choke well directly above the heat crossover passage in the intake manifold. As it heats the coil expands and releases tension on the carb’s choke system at a set rate determined by the heat present in the coke well. Without this heat the spring, set for proper cold running, will continue to choke the carb well into the warn-up cycle and may not release all its tension at all. After market street carbs will have a completely electrical choke system not dependant on crossover heat. Not an option for the original six-pack center carb.
Mid 70’s and up motors usually came with a divorced choke with built in electrical heating elements to have the choke come off even quicker than would be normal with only crossover heat, mainly for exhaust emissions requirements. This heating element ran quite hot and pulled more current than would normally be acceptable powered up thru a complete run cycle. A temperature sensitive timer (choke heater control) was used to shut off current flow to it after about 10 mins or so. As mentioned in the first post, these original choke heater controls were troublesome from the beginning. Tended to burn the contacts internally and stop current flow to the heater.
So I took a heated choke spring assembly from a mid 70’s big block, trimmed the spring mount, that includes the heating element, and riveted in place of the mount on the Holley six-pack choke assembly. After going through 2 NOS choke controls ended up building a relay based IC controlled timer to shut off full voltage to element after about 6 mins. at which time current continues, at a much reduced rate, through a high power resister to keep the spring from cooling down. Found that at my 180` normal operating temp, after mainly cruising conditions, the choke spring wouldn’t stay completely relaxed without some additional heat.
End result, although this car is not a daily driver, with the Edelbrock heads and headers, it starts up perfectly when cold and is off fast idle in about 4-5 mins.

Doug

Wow, good info! Where did you get this IC timer, and does it have a part number?

Quote:

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building a relay based IC controlled timer to shut off full voltage to element after about 6 mins.

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I would like to do this on my car. Did you run the supply voltage through a relay? What circuit under the hood did you hook it to? Could you show a wiring diagram?
Thanks
Jess in ky

those of us electronically challenged need part #s and a diagram. This is backyard engineering at its best. Destined for the archives.
Ron

The IC timer is a LM555, sourced mine from Radio Shack. Do a search on LM555 you find many schematics, the values of a resister and a capacitor determine the timing. I experimented on my bench to come up with about 5mins after ignition “on”. The timer controls a simple Bosch type relay to handle the heater current. Power comes from the ignition “run” circuit at the ballast resister. The original application for the heated choke spring I used was a 74’ big block thermoquad like this one.

The original choke control looks like this. Again, should you go this route it will likely fail pretty quickly. I did take the power resister off and used it on my home built timer control.

Pictures borrowed from currently running ebay auctions BTW.

I will post more pics and a diagram of what I did next week, I have much work to do on my car this weekend as it is off to the body shop next week for final paint.

On my six pack set up I use the original stove type choke with the exh crossover blocked. I have the choke spring adjusted (yes, there is an adj screw) to just barely engage when cold. This coupled with the fact that I don't drive it in the winter (much) seems to work OK. I have to tickle the throttle for about 30-60 seconds before it will idle on it's own. Then I stay out of the throttle for the first mile or so and after that it's good to go!

Some of the original choke springs had the ability to adjust, the one came with my MP reissue six-pack hardware is not adjustable. Besides, backing off on the initial spring tension just leans out the choke or de-tunes it. There are plenty of these cars running around with their chokes de-tuned or disabled. Fact is, blocked crossovers or not, a properly street tuned six-pack set-up will be quite cold blooded without a fully functional choke. Some parts of the country worse than others no doubt. A lot of people seem to just accept poor cold drivability, that’s fine by me, I choose not to. Not preaching here, someone inquired about my choke mod, I provided the info.

There is always the venerable cable-operated manual choke conversion. It's old school, but it can work great.

I had the choke horn milled off on my center carb on my '70 sixpack car, but the fast idle cam is still functional. It can at least keep the engine fast idling for those first few minutes without having to do it by foot with the accelerator pedal.

For my '68 slant six, I bought an electric choke conversion that uses a small temperature sensor that bolts to the motor to help time the choke's closed/open cycle. It works great.

It's a little hard to see in this pic, but look where the old style choke stove was and you can see the new electronic choke. There's also a small black sensor bolted to the head near the center intake manifold runners that modulates the openning timing as it senses the heat from the engine.

This is where I got mine after learning about it on Slantsix.org
http://www.carbsonly.com/carbs/carbschoke1.htm

i have 6k on my car with eddy heads, cold climate. i had same problem. not enough heat to pull off choke. disconnected the vacuum line to the pod on the choke to see if this would allow the choke spring to pull off the choke, and to did. choke works fine now.

Would be interested in this setup also. Especially with the Electric timer. Any suppliers/ and or parts list are greatly appreciated, along with more close up, clear pictures.

Would rather buy one of these, then cuss at my non working factory setup. Anyone want to (or willing) make up a few of these? Thanks!

BTW, could we "sticky" this? I'm sure there are more of us that would like to refer to this later that have Eddy or aftermarket alluminum heads.

On some of the spring assemblys there is a 'set' screw for lack of a better term that you can adjust to determine when the lever engages the hook in the snail spring. It actually has some marks or graduations on it. If your spring assy is rusty, etc you will need to wire brush it to clean it up enough to see the marks.

It doesn't take much to change the adjustment and put a small mary on the starting point incase you want to return to it.

The older and original choke spring assemblies had a lock nut where the pivot shaft mounted to its bracket. Rotating the slotted shaft the spring was mounted to would allow for slight adjustments to cold running spring tension. Later versions of the divorced chokes had the shaft pressed into a fixed position to prevent adjustment. The reissue choke that came with my MP six-pack hardware kit was fixed and non-adjustable. If you are careful you can force this shaft to pivot thereby relaxing the spring tension. Again you would be de-tuning the choke to allow the choke to be fully open at operating temperature. When cold there will be insufficient spring tension to provide a fully functional choke. It would be only slightly better that wiring the choke open or disabling the choke all together.

As for installing a Holley or aftermarket choke assembly to the center carb, the limited space available in that area rules that out. The fuel line to the rear carb and the front carb’s vacuum actuator directly conflict with this space. The mounting points cast into aftermarket Holley’s to mount the aftermarket choke are not present on the six-pack center carb. In my case, I also wanted to keep the original appearance.

Removing the vacuum line from the “pod”? The “choke pull-off”, is there to open the choke slightly after start-up to allow air for the cold mix. I can’t see how blocking off that vacuum line would resolve anything, would make matters worse I suspect.

This is my home built timer/choke heater control.