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Author Topic: Correct Bi-metal choke kit  (Read 1108 times)
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« on: May 07, 2014, 09:34:15 PM »

Getting my car back together now except for one problem. I cant seem to find the correct bi-metal choke kit for my carb, Q-jet 7027210. I have gone through 4 different vendors, and cant seem to get the right kit. On this carb, the choke spring needs to retract instead of unwinding, and it has an off set choke rod. Anyone know where I might find the right kit? Lots of bucks sitting in a box on the shelf.   Angry   
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Ed Bertrand
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« Reply #1 on: May 08, 2014, 09:30:29 AM »

While there are exceptions to the rule (yours is not one of them), Q-Jet chokes "pull down" when they're cold, and (factory) Holley chokes "push up" when they're cold (see below).

One of the few exception is the 68 Corvette 427/390, but your carb isn't that one.

Unless someone has changed the choke pivot on your carb (very possible), you should be using the choke that pulls down when it's cold and pushes up as the engine warms up.

Ed

« Last Edit: May 08, 2014, 10:17:30 AM by Ed Bertrand » Logged
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« Reply #2 on: May 08, 2014, 10:08:52 AM »

Thanks Ed

Im going to get a hold of Custom Rebuilt Carbs, where I purchased the carb and try to get some answers.
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Ed Bertrand
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« Reply #3 on: May 08, 2014, 10:18:23 AM »

post a picture of your choke pivot and I can tell you if you have the right one or not.

It should look like (or similar to), the picture I've attached. Also, are you using a stock intake manifold or aftermarket?

Ed

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« Reply #4 on: May 08, 2014, 11:08:15 AM »

I will try and get a picture up. (May need Grandson's help). The intake manifold is stock.
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Mike S
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« Reply #5 on: May 08, 2014, 11:18:38 AM »

 On my one 67 BB, I had a replacement choke coil and it was opposite in operation.
You can slide the coiled ribbon spring off its shaft and reverse it on the and get it to work opposite.
It's a snug fit but it does slide off.

Mike
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« Reply #6 on: May 08, 2014, 12:20:36 PM »

On my one 67 BB, I had a replacement choke coil and it was opposite in operation.
You can slide the coiled ribbon spring off its shaft and reverse it on the and get it to work opposite.
It's a snug fit but it does slide off.

I recently replaced mine and after installing it correctly it was moving the wrong way as it heated up.  I compared it to the one I replaced and warmed each with a lighter and one contracted with heat and one expanded even though they were oriented the same way.  I corrected the new one I had by doing exactly what you did but I did have to bend open the frame a bit to get it out.  BTW, I've studied those drawings in Ed's post above and something's not right because both the Q'Jet and Holley springs are reversed in the hot position compared to the cold exactly as if they had been removed and flipped over like we did.  (look at the curl on the end of the spring in the drawing to see what I mean.) I didn't know about the Holley vs. Q'Jet difference so thanks Ed for explaining my mysterious reverse spring. But clearly there's two issues here.  One is the Holley vs Q'Jet difference which is solved by the spring orientation but the other is that the bi-metallic spring, depending on how it's made can either expand or contract with heat. So you have to know both to get the spring moving in the right way for the application.
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Mike in Northern Illinois
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Ed Bertrand
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« Reply #7 on: May 08, 2014, 12:26:53 PM »

Quote
BTW, I've studied those drawings in Ed's post above and something's not right because both the Q'Jet and Holley springs are reversed in the hot position compared to the cold exactly as if they had been removed and flipped over like we did.

That's because I just used Photoshop to copy and edit the two drawings. It's not "true to life", just a representation showing the movement of the coils.

Ed
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« Reply #8 on: May 08, 2014, 12:48:38 PM »

That's because I just used Photoshop to copy and edit the two drawings. It's not "true to life", just a representation showing the movement of the coils.

Ed

OK.  I'm sure I overanalyzed them because of my mysterious reversing coil.  Any idea why some contract and some expand with heat or is there a manufacturer out there selling reverse contracting springs?  I guess I could speculate that some manufacturers solve the Holley vs Q'Jet difference with the spring orientation and some with the spring movement direction when heat is applied.  I checked and I did buy a Q'Jet spring and it was clearly on backwards.  It now matches the first drawing on the left side.
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Mike in Northern Illinois
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Ed Bertrand
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« Reply #9 on: May 08, 2014, 01:18:02 PM »

I'm no mechanical engineer, but I do know that ALL bi-metal springs contract with cold and expand with heat. As a matter of fact, everything in the universe contracts with cold and expands with heat. That's just physics.

I believe the differences between the two types of springs (Rochester -vs- Holley) is the way their made (?)

Bi-metal coils consist of two strips of different metals, which expand (or contract) at different rates as they are heated (or cooled), welded together back to back. (That part I'm positive on!)

(Here's the part I'm not so sure of) The metal that expands faster is on one side of the strip for one type of coil and on the other side of the strip for the other type of coil (?) This would make one coil move down when heated and the other move up when heated and vice versa, but again, I'm not sure if this is actually correct.

I'll see if John or any of the other guys can add anything to this.

Ed
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« Reply #10 on: May 08, 2014, 02:17:02 PM »

I'm no mechanical engineer, but I do know that ALL bi-metal springs contract with cold and expand with heat. As a matter of fact, everything in the universe contracts with cold and expands with heat. That's just physics.

I believe the differences between the two types of springs (Rochester -vs- Holley) is the way their made (?)

Bi-metal coils consist of two strips of different metals, which expand (or contract) at different rates as they are heated (or cooled), welded together back to back. (That part I'm positive on!)

(Here's the part I'm not so sure of) The metal that expands faster is on one side of the strip for one type of coil and on the other side of the strip for the other type of coil (?) This would make one coil move down when heated and the other move up when heated and vice versa, but again, I'm not sure if this is actually correct.

I'll see if John or any of the other guys can add anything to this.

Ed


Ed, I guess I phrased my question wrong.  I was wondering why a manufacturer would make a spring that would contract with heat rather than expand, not why that would occur.  I understand that everything expands with heat but when you bend a piece of bi-metal into a coil it depends on the direction it is bent (with or against the metal that expands more with heat) that determines how the coil behaves when heat is applied.  With respect to the end of the coil (which is all we care about here in moving the choke linkage) the up or down direction with heat can be controlled by just flipping the spring over as in either of your Q-Jet vs Holley drawings.  If either of those springs is wound the other direction they will behave the wrong way unless flipped over again.  As I posted above, I have 2 springs that act differently when heat is applied. Both could be made to work for either a Q-Jet or Holley simply by removing them from the bracket and re-installing in the opposite orientation as Mike S. and I did.  The only reason, I'm belaboring this is because, like the original poster, I was scratching my head when I bought and installed the new spring because I assumed they all expanded when heated.
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Mike in Northern Illinois
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« Reply #11 on: May 08, 2014, 02:22:04 PM »

I'm no mechanical engineer, but I do know that ALL bi-metal springs contract with cold and expand with heat. As a matter of fact, everything in the universe contracts with cold and expands with heat. That's just physics.
....

Except for the common H2O which expands when it gets cold enough to freeze; but of course that's a change of state... from liquid to solid.
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Gary W.  /  69Z28-RS, 72 B 720 cowl console rosewood all tint
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Ed Bertrand
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« Reply #12 on: May 08, 2014, 02:33:47 PM »

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As a matter of fact, everything in the universe contracts with cold and expands with heat. That's just physics.

Well, I was informed by Rich that my answer was right enough, but I was wrong about everything in the universe contracting when cold and expanding when hot!!! There are materials that shrink when heated (i.e. Carbon fiber in the axial direction being one of them), so now my universe it turned upside down!!!

But as for why the factory used two different styles of coil when one would work just as well for both types of carbs just by flipping it over? No clue, but there must have been a reason. The General didn't do things just to do them. If they could save 1 cent on each car by using one coil they would have.

Ed
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« Reply #13 on: May 11, 2014, 03:16:24 PM »

Here is a shot of the carb
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« Reply #14 on: May 11, 2014, 03:28:07 PM »

Hope this is a better picture.
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