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Cd150 autochoke adjustment 79 Midget

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neilh

neilh

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Single Stromberg CD150 carb on 79 Midget - I replaced the air mass unit on the carb, Haynes says to align the mark on the air mass to the datum on the main assy - the new part from Moss has no mark on it, niether has the old one. Anyone know how to set it correctly.
- my engine when cold idles - if you can call it that! at 4,000 until warm, then dies to about 1,000. All other adjustments are per haynes and correct.
 
Hi Neil, are you talking about the bimetal unit that has the coolant going through it? Not sure what you meant by "air mass". There should be a line scribed on the outside of the bimetal housing, which aligns with a matching scribe mark on the plastic spacer and on the carburetor body. If the marks really aren't on the bimetal part (the one that has the coiled up strip that moves with temperature), then the service manuals say to put the bimetal into a pan of boiling water and make a mark that aligns with the tip of the bimetal strip once it's fully warmed up. Unfortunately, it doesn't clarify which edge of that tip you were supposed to go by, but maybe it's just supposed to be in the ballpark. Hope this helps!
 
<div class="ubbcode-block"><div class="ubbcode-header">Quote:] Unfortunately, it doesn't clarify which edge of that tip you were supposed to go by, but maybe it's just supposed to be in the ballpark.[/QUOTE]

It is the "outer edge" the one that is directly after bend from the coil shape. The continuation is just a loop.
 
If you are running 4000rpm cold, you may need to adjust your fast idle screw. There are two idle adjust screws on the late CD150. One is the stop screw and it is a small screw inside a set nut. The other is a spring loaded screw that sits just aft of the stop screw. This one is the fast idle set. Once you have the spring aligned, if you still have a high cold idle, you can try backing out the fast idle screw until you get it where you want it. Then adjust the stop screw to compensate once the car warms up.
 
Sparky - I tried the hot water trick, made a mark - no difference. I ran the car until it got to temp, then rotated the bimetal strip assy to ensure it was fully in the hot position, no difference. The until appears to be operating correctly, it does open the throttle when cold, close it when hot - just not enough.
Morris- the stop screw is correctly set and the cold start unit does go all the way to the correct postion when hot - its the throttle that is still held open to far, and the fast idle screw when backed out still does not close it enough!

So .. still looking for the problem.
 
The only thing I can think of now that you say the fast idle screw will not shut it down is a air leak at the carb or manifold.
 
Does sound like a strange one for sure. Do keep in mind that changing the fast idle screw changes idle speed no matter what the auto choke is doing. The slow idle screw only comes into play once the fast idle cam is fully off.
 
When the fast idle cam is fully off - i.e the water jacket is hot, i can adjust the slow idle to around 900 rpm, when i blip the throttle it will usually come back to around the same, sometimes less. I'll mess with teh fast idle again and see what happens.
 
sparkydave, thanks for teh link - that really helps - now to remove the sob one more time!
 
I have been thinking about this problem... and here is what I came up with. Maybe all you need to do is turn the heat mass assembly. It sounds like your getting full engagement of choke, which you might need if it were 20 below, but not at this time of year. After all, you want your to choke shut off BEFORE full operating temp, right?
 
Morris, i tried that, but the design of the cam assembly seems to want to always apply full choke if the water jacket is cold. But I'm going to give it another try, just in case!
 
You may try loosening the three screws that hold the mass assembly to the chokes assembly and slowly turn the mass assembly counter clockwise, blipping the throttle along the way until you get a reasonable cold start idle level (@1200 rpm). May take a few tries if the car warms up too much during the process.
 
Morris - tried that but could not get below 3,000. I found a great article that talks about the water choke

https://www.paulbunyan.net/~jasko/choke/

and i'm going to work through it line by line!
 
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