Automatic choke adjustment problems on a 4GC carb.

[Peter Greenway]

I have a 63 Series 62 with a Rochester 4GC carb and I'm having problems adjusting the automatic choke. I have read the workshop manual and Rochester set up manual and tried all that is written but I either get the choke to set ok but then won't come off fast idle to a slow idle or I get a good slow idle with a hot engine but when it's cold the choke won't set. I've adjusted the thermostatic spring to one notch rich from the middle position and when hot the choke valve is vertical and just "twitches" slightly when the throttle is opened.
I have tried bending the choke rod slightly either way to move the fast idle cam up or down and tried adjusting the fast idle screw to set the choke when cold, but when the engine starts either the fast idle cam won't drop to the second notch or if it does then it won't drop to the slow idle position when hot.
It seems I can't find the happy medium where the choke sets, then comes off to a slow idle when hot.
Any suggestions on how to adjust it please?

[2danreed]

I had this problem on my '64 series 62 sedan (mine has the Carter ABF). The heat tube that runs from under the intake manifold to the choke housing is probably shot (corrosion eats them up). This past year I installed an electric choke and I've had much better performance.

Dan

[Peter Greenway]

Thanks for your suggestions Dan & Steve, but unfortunately I know that is not the problem as I have replaced the heat tube as it was broken, and I have cleaned out the thermostatic housing and piston and made sure it is working correctly which it does by pulling the choke valve fully vertical when the engine is hot.
My problem seems to be when the fast idle screw is correctly adjusted to hold against the fast idle cam at the bottom to set the choke, when the engine starts and the cam drops to the fast idle position as the engine warms up the screw holds the cam and stops it dropping to the slow idle position. If I adjust the screw back then I can't get the choke to set when cold.

[fishnjim]

Partly due to operation.  One must step on the pedal once fully to "set" the choke linkage before starting and not pump it during starting or heat up.   This is where a well functioning ignition system plays in.  ie starts on the first turn.
If you don't do that, it just starts in whatever position it was left and won't idle properly.   
The carb idle speed has to be adjusted in concert with the timing to get the base idle/timing correct.   If you don't, they both can be off.
Visual inspection: I like to compare the linkage to the pictures to make sure it's all installed correct.   Easy to turn one piece over, bind, or miss something.   
The choke plate has to open fully/properly for the linkage to drop off the idle cam.  So if that adjustment is off, it won't work right.   The parts are "linked" so all work in concert.   If one just starts adjusting one w/o the others chaos ensues.
It could be a number of "wear" factors adding up, but no way to know from the internet.   Vacuum leaks, etc.
If the carb is gummy & outside/linkage is dirty it might be best to pull it, give it a soak in carb cleaner and rebuild.
I wouldn't mess with bending or other tweaks, until the condition can be assessed.  May do more harm than good at this point.   That all has to be done in a methodical order.
Sometimes we expect too much from a 50+ year old machine/technology in less than stellar order and with less than complete repair knowledge.   Are expectations are also "spoiled" by the modern electronic systems.   

[Dave Shepherd]

To add, vacuum pulls the heat up the heat tube, if that passage is plugged the choke will not open all the way, it can be checked by feeling for vacuum  with the line disconnected at the choke.

[Peter Greenway]

Thanks for your replies. I definitely set the choke the right way with one step on the pedal, then leave it alone and it will set, engine starts and cam falls but then fast idle screw holds cam on fast idle and stops it dropping off fully.
I have adjusted the timing and set the low speed idle correctly all with the choke valve in the fully open position.
As far as I can see all the linkage is correct to the pictures in the workshop manual.
I know all about "chaos" as I've been there several times! More than once I've reset everything and started again learning a bit more each time.
You could be right about "wear" in the parts. All the linkage is clean, free to move and I've lightly lubed it. I've run carb cleaner through with the engine running, but not taken it apart.
I'm just baffled by the fact that if I adjust the fast idle screw so that it drops off the cam when hot, then the choke will not set when cold as the fast idle screw will not touch the cam with enough pressure?

[2danreed]

Well...I'm at a loss as to what additional to add, but I was wondering if it were possible to add a couple photos of your carb linkage. That may help readers evaluate the situation.

[Peter Greenway]

Good idea about the photos.
I have attached showing;1. Fast idle screw dropped off cam; 2.Screw off cam and showing choke valve open; 3.Choke set with my finger holding throttle open; 4.Fast idle screw at fast idle position on cam.
Hope these help.

[Peter Greenway]

Well, a little progress. I've just invented the world's first (probably not!), "semi-automatic" choke. I've found with the slight adjustments made that if I press the throttle pedal down slightly to open the throttle and allow the fast idle cam to come up and choke valve to close, l then crank the engine and when it fires with high revs immediately start to slowly release the pedal until I hear the revs are on fast idle with the screw on the cam in that position, hold it there for a few seconds, then take my foot off the pedal and the engine will warm up. Then when the spring is hot enough the choke valve will open fully and the fast idle cam will drop and the engine will then go to slow idle.
So far it's worked OK for a couple of times, so I'll use that method until I can work out (or you clever guys out there can tell me!) how to get it to work "fully automatically". 

[Peter Greenway]

Well since June until now October, I've been working on the choke system (although not all the time), and have finally found out what the problem was. It was me! I thought the second notch on the fast idle cam was at the bottom, but it's not. It's at the top. After reading the manual for the hundreth time I finally figured out how it's supposed to work. I straightened out the choke rod, (which I had bent to get the cam to sit higher) so that with the fast idle screw adjusted to rest on the second notch, the choke valve had a clearance of 40 thou at the top with the carb back plate. (Actually I could only get 80 thou, but I think that is because of wear in the linkage and rods). After one full press down on the throttle pedal to set the fast idle cam in this position, the engine fired up first time and kept running at an approximate speed of 900 to 1200 rpm whilst it was warming up. Once the engine is warm enough the choke valve opens and takes pressure off the choke rod. When the throttle pedal is pressed to drive off this takes the fast idle screw off the cam and allows it to drop so that when the throttle pedal is released to slow down the fast idle screw is off the cam at the top and the throttle closes to a slow idle position. I have left the engine to cool down for 24 hours then pressed the throttle to set the choke and it fired up first time. I then left it for 7 days, but found that the throttle needed to be pressed down twice (I guess to operate the accelerator pump more), and then it fired up first time again and kept running on fast idle.
So I think the choke setup is 90% automatic, but with a 10% manual input at the end to get onto the slow idle speed.
I'm now adjusting the fast idle screw by very small amounts to get it set it to the best overall position.
I hope this information helps anybody else with similar problems. Moral of the story; keep at it. Don't let it beat you!

[Big Fins]

It only beats you if you give in to it, or give up!

[Daryl Chesterman]

Once the engine is warm enough the choke valve opens and takes pressure off the choke rod. When the throttle pedal is pressed to drive off this takes the fast idle screw off the cam and allows it to drop so that when the throttle pedal is released to slow down the fast idle screw is off the cam at the top and the throttle closes to a slow idle position.

This really should say: "Once the engine is warm enough the choke valve opens and takes pressure off thefast idle cam linkage.

When the throttle pedal is pressed to drive off this takes the fast idle screw off the cam and allows it to drop

...

This is true, but if you give the throttle a little "blip" before putting the transmission in gear, the fast idle cam will drop down and the engine will be at hot idle speed, and you can engage the transmission at a reduced engine speed and not get the jerk that you will get if the transmission is put in gear at the fast idle speed.  The automatic choke is "automatic" in that with a cold engine, pressing the throttle automatically closes the choke butterfly and sets the fast idle cam.  Then as the engine warms up, the choke butterfly "automatically" opens and takes pressure off of the linkage for the fast idle cam.  That is the end of the "automatic".  Then, as you found, you have to release the fast idle cam by pressing the throttle to allow the fast idle cam to drop down—the "manual" part.  Glad you figured it out!

It is normal to have to "pump" the throttle a couple of times when the engine has not operated for a week or more.  If you are using ethanol gas, the volatility of it causes it to evaporate and that results in a lower fuel level in the float bowl, and you do not get a full stream of fuel with just one pump of the throttle.

Daryl Chesterman

[Peter Greenway]

Daryl, Thanks for the correction and additional bit of information.
Always good to know and worth remembering.
Cheers.

[fishnjim]

Looks like to me that one linkage is badly bent, source of your ills(?).
I'll have to see if I can get you a picture of mine/or one and what it should look like.   Sorry, I haven't been following.   
I think I have the 4GC manual, but clean talk has been interfering with posting some pdfs.   I'm pretty sure i posted a copy before all this so if you search the forum, you might find it faster.
If this was me, I'd have pulled that carb at the outset and rebuilt it.   Taht way you know it's right, not someone's attempts.

[Peter Greenway]

Yes the choke rod was bent because I bent it thinking that was the right thing to do. I now realise my mistake and bent it back to where it should be to get clearance at the top of the choke valve and drop the cam correctly.
Thanks.

[Peter Greenway]

I'm going to end this topic now and I will not be monitoring it any further.
Many thanks for all the helpful advice and information.

Drive safe!