Idle speed on choke
#1
I'm sure this is a simple adjustment but I cant think which one!
I have just rebuilt my carb and this is how the engine runs now.

1 - she starts instantly
2 - when she is hot she runs and idles fine

The problem is when she starts the "cold start" speed is low and is on the edge of stalling unless I leave her for a few minutes to warm up.
If I open the primaries then the idle speed is too high when she is warm.
It's an automatic choke and could it be she is a bit rich ( not enough air to burn the fuel?) and if I Lean her off a bit will she run faster on choke?
I've set the A/F screws OK I think as she runs strongly with no hesitancy.

Any ideas?

351 Cleveland / Holley 4150

Thanks
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#2
Look at the choke blade, follow the arm/ link from the choke blade down to where it hooks into the fast idle cam, there should be 2 or 3 steps on the idle cam. I believe there should also be a plastic block with a screw going thru it to adjust the idle speed when it's on fast idle. With the engine cold / overnight. Push the accelerator all the way to the floor to activate the choke. Choke blade should close all by itself, if it doesn't you need to set the choke as well. (Setting the choke) After you pushed the accelerator to the floor, loosen the screws on the choke housing rotate the housing until the choke blade just closes, continuing turning about another 1/8 inch, or one more notch if your housing is marked. Snug the screws, now take you finger, and stick it down the carb pushing the choke open it should open easily with a little resistance, but not much. When you pull your finger out it should close by itself, if it snaps shut, it's to tight. Once you have the choke set correctly. Make sure it is on one of the steps on the idle cam. (You may have to push the accelerator again after setting the choke) Start the car, you can now adjust the fast idle speed probably 8 or 9 hundred rpm. Or what ever sounds good. As long as it's a couple hundred above the regular Idle speed, you should be good. Hope it helps. 

JTS
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#3
There are usually explicit instructions for choke settings.  On these older carbs it typically involves using specific drill bit sizes between the air horn and choke plate to set things like, primary and secondary (if is has one) choke pull-offs, fast idle screw setting on a particular fast idle cam location.  These get is very close to correct. With later model carbs, instead of using drill bits between the air horn and choke plate, and angle measuring tool is used to measure choke plate opening for all those settings.

After your choke settings are made, one simple test is start the motor cold, after running a few seconds to get off the fastest idle setting, put the trans in gear, and with one foot on the brake load the motor a little, it should not die, stumble, etc.  If it does, there are choke settings that are not correct.

I don't know how much help this is.  Choke settings can seem complex the first few times.  For my old cars and trucks I use manual chokes.
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#4
I'm reading all your posts and I'm learning all the time and think the problem I have is due to me changing the fast idle cam to a new Red one.
The old one was not in good nick and looked like it needed replacing, I did place them side by side and they looked the same but who knows.
I've been adjusting the fast idle and now understand how it all works but it's so hard to see any of it and to adjust it especially with the vacuum secondary in the way so I've been using a mirror and am trying to get it onto the middle range (1,100 rpm ish) cam.
It still runs great, no stumbling or hesitation and pulls strongly it is purely the "on choke" startup, when hot it idles perfectly around 7/800 rpm and 600 rpm in D.
I believe the carb jetting etc is perfect as it was set up on a dyno a couple of times ( a long time ago but very little use since) and when I got her it was perfect I reckon, so it can only be things I have done ( rebuilt carb gaskets etc and fitting the red idle cam) but I kept the A/F screw setting ( about 7/8 of a turn out which I know is possibly low according to some settings) so it shouldn't have changed much.

Thanks again
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#5
Sounds like you're in the ballpark a little more fiddling and you should be close to 100%  Cool 

JTS
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#6
(08-05-2021, 07:44 AM)JTS71 Mach1 Wrote: Sounds like you're in the ballpark a little more fiddling and you should be close to 100%  Cool 

JTS
I've got it onto the middle cam so it idles at about 1,100 rpm on choke but it's not as "smooth" as it used to be on choke, if you dont give it a few minutes to warm up it wants to stall.
But again it starts easily and when hot idles lovely so as I'm off on holiday now she's having a rest from me prodding and poking her!
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#7
well I've now put a vacuum gauge on her and have got it up to 17" on an 800 rpm tick over ( 600 rpm in D)
The A/F screws are now 1 1/2 and 1 1/4 out (against the original 7/8 when she  ran great) with a very clean exhaust ( no petrol smell at all)
the choke flap opens about 1/8 - 3/16" straight away so the piston is working fine, my issue is it doesn't "warm up as sweetly" as she did before and will stall if put into D straight away but runs fine no stumbling etc when hot.

I've set the choke flap cold to being "just closed"
New spark plugs as well same gap as before
The "on choke tick over" was low before ( 800 /900 I think  Huh  ) but had no issues with driving off etc that I remember ( colder weather then) and now I've set it to 1,200,  the only thing I've changed is the carb spacer from 0.275" to 0.500" as the old one was cracked and had been repaired a few times, could the small increase in chamber volume make much difference to the required jetting?

All this is after I changed the lifters but I think I've set them correctly as she seems to perform well normally and as before no rattling on start up etc and rebuilt the carb with new gaskets etc.
I'm tempted to shut the A/F screws down and drop the fast idle cam back as well just to see if it get nearer to how she was ( which was very very good)
Am I just being too picky and need to let her warm up for a few minutes first?

Cheers
Jeff
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#8
Every thing you have repaired or replaced has a cause and effect on your runability, idle, warmup time, etc. Everything is interconnected. Change one thing, and it changes another. Change several at once and all bets are off. As you can't figure out which one has had the most effect. Second point, there is a reason manufactures went to electronic fuel injection. The issues you are facing are one of those reasons. As far as being picky. How long is you patience?  Confused

My thought is make it the best your can, starts well, Idles well, so what if it takes a few minutes to warm up. 

JTS
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#9
(08-21-2021, 01:54 PM)JTS71 Mach1 Wrote: Every thing you have repaired or replaced has a cause and effect on your runability, idle, warmup time, etc. Everything is interconnected. Change one thing, and it changes another. Change several at once and all bets are off. As you can't figure out which one has had the most effect. Second point, there is a reason manufactures went to electronic fuel injection. The issues you are facing are one of those reasons. As far as being picky. How long is you patience?  Confused

My thought is make it the best your can, starts well, Idles well, so what if it takes a few minutes to warm up. 

JTS
All good points, and having taken the idle off of the fast idle cam ( as I think it was originally) it seems better, my patience with her is good ( at the moment) and I'm going to leave well alone and get used to it as it is.

On another note we have just now brought in E10 petrol, so I will have to pay extra for the "old E5 super" at $8.77 an imperial gallon from now on, how do you cope with E15 / E30 over there with regards to  -
Solder on the floats
Water absorbtion 
fuel  pipes
We are hearing horror stories over here with the side effects on old cars here with just the E10.
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#10
Most 70's cars will tolerate E10. I had my 71 Mach1 when it first came out mid 70's, and it was a pain, as it plugged the fuel filter 3 times in a week from all the crap it loosened up. Once that was over, never really had an issue.  Now if an old car sets very long with E10, it causes lots more trouble. As it deteriorates the rubber lines, seals, styrofoam, and even some plastics, much quicker when not being driven regularly. The manufactures were pretty quick to correct the problems. But that was about the same time fuel injection was starting to come in the picture so carbs, floats, crappy rubber, and the issues from E10 weren't as big a priority anymore. So they / aftermarket, started suppling Brass, or a hard plastic floats, to replace the styrofoam ones. As sometimes the styrofoam floats would absorb fuel, and become heavy causing the carb to flood over. which really screwed things up.
But all in all, other then a few hiccups, E10 hasn't been that big an issue for the most part.

JTS
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