Hi everyone

I just rebuilt my engine but the old 1920 on it has me scratching my head. I took it apart curiously when I first had the engine off and then put it back together again. I think I got everything right, as it idles cold fine and there is a stumble off idle (flooding or too lean) but that is corrected more easily than what I am about to ask.

The thing that bothers me is that before I had the 1920 off the manifold it had that action where you would stomp on the accelerator pedal and the choke would turn on for easy cold starting (I have the automatic choke). Then you could stomp on the throttle again and it would snap back to normal. Now it doesn't have any action at all. I can manipulate the choke plate by hand, and it has resistance like its spring is still working, but I think I forgot to connect something. I've looked at a bunch of the Holley 1920 diagrams floating around on the search engine but nothing seemed out of the ordinary. A bunch of the linkages are loose, so I am wondering if I have some bending to do (even though the carb had this action before I took it off with no linkage bending).

So, how does the snap-action on/off work? What connections enable it? I can't give you much information because I don't know how to describe what's happening. I can place the fast idle cam on the fast idle screw by hand, moving the choke mechanism until its flap is fully closed (on). Then I can move the throttle until the hammer at its tip hits the fast idle cam and opens the flap (choke turning off), albeit with less force than I remember it doing.

So, would anyone be able to tell me what needs to be connected or adjusted?

Also, I am missing the stainless steel cup that goes underneath the thermostatic element that mounts to the exhaust manifold (and its gasket). Would I be able to get this from a place like NAPA?

Thanks for any reply. Runs nice otherwise (have to defeat that stumble, maybe my float is set too low)

"Also, I am missing the stainless steel cup that goes underneath the thermostatic element that mounts to the exhaust manifold (and its gasket)."

You're gonna need that cup to make the thermostatic element work.

You've got the "snap" action thing a little wrong in your head.

Here is a better explaination of what happens. With the engine completely cold, the choke is typically open from the last time it was driven. A properly adjusted thermostatic element is trying to pull it closed, but there is the fast idle cam holding it open.

Pressing the pedal to the floor releases the fast idle cam and the thermosatic element should "snap" the choke closed. There is no system which makes it "snap" back open cold, but the vacuum choke pull off should partially open the choke plate once the engine starts. The thormostatic element will open the choke the rest of the way as it warms up.

For Bog, Check for vacuum leaks and main jet size.

A stumble could also be timing related. Lots to learn.

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1980 Aspen 225 super six

Yeah, I accidentally did my timing with the vacuum advance connected!

It just makes me wonder what is misadjusted because it worked fine before. Maybe I just need that cup, and the extra width will shim out the choke for me. I hope Napa has it, I am stopping by there today.

The vacuum pull-off never worked, its linkage was spread way too wide for it to effect the small choke pivot everything else is connected to.

In the end, I'm thinking my thermostatic choke has lost its spring action somewhere along the line when it was off the engine.

Just wanted to make sure I wasn't missing something crucial, like an extra spring. (Turns out I might be--the bimetal element)

But let me clarify something; when the choke is on, the choke flap is closed (to "choke" the engine with more fuel than usual), correct?

Yes, on = closed; or at least in my descriptions. I don't expect you'll find the cup at napa, but it's worth a try. Perhaps someone has an extra that they'll sell you in the parts section.

Getting the choke thermostat fixed and the pull-off adjusted will help with starting quite a bit.

Let us know when you get that far, and someone will offer more direction in correcting the bog.

You'll collect info over time if you just keep reading and tinkering and eventually you'll "see" problems that where always there but overlooked

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1980 Aspen 225 super six

I want to replace the thermostatic choke (electric) but I can't find a reference online. The part number is CV129, the brand is Standard (Hygrade etc). Even Standard itself doesn't have it in its parts database! Is it out of production?

Another view of the choke operation. I got a good one and looked at it closely as I never had a mechanical one that ever worked. The choke element itself that bolts into the manifold well is extended when its cold (seems like it would be the opposite, eh ) Anyway, that springy extended state pushes the choke valve closed and it is with a snap once you press the accelerator once on a cold morning, that snap also moves the fast idle cam up into the throttle lever, kicking it open a little. When the car is started, the well starts to heat up and the spring starts to relax, but it doesnt pull the choke open, the choke itself is under light spring pressure to open itself so the spring only pulls away from the choke rod, the choke spring on the carb body actually pulls itself open. It can only pull itself as fast as the bimetallic spring relaxes, and that is where you tap the gas again , releasing the fast idle cam gravitationally and it drops a notch or 2 setting the idle closer to basline idle. Pretty cool to watch it happen. Same idea with the riser on the manifold. I looked at that thing for a few minutes until I realized the spring only does one function, and that is to raise the diverter into carb heat position. It keeps it there under tension until it gets warm enough and starts to "unwind" and then the exhaust gas flow pushes the diverter back to where it likes it to be, doverting the gas toward the exhaust flange. I was under the impression that the bimetallic springs were more like the ones in a "stove" setting like on the side of a carb. Those are a captive type whereas the spring actually pushes open and pulls a rod through the bimetallic spring heating action to manipulate the . The divorced choke we have and the exhaust riser use an opposing force (main body spring and gas flow) to reset to normal operating temperature. The non operational bi metallinc springs on my friends car both didnt do anything when heated, no movement, or very small weak movement.