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  #1  
Old 09-21-2008, 04:52 PM
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Question 67' 250S Carb Rebuild question choke

I have the carbs apart, and on the rear carb the choke has a triangle diaphram. The gasket on it doesn't line up over the holes, and without it lining up, the ''flat'' spot on the metal part of the the shaft of the diaphram doesn't go over the ''loop'' metal part on the spring tension inside the choke area. I can't move the gasket any at all. I think the gasket is put on wrong, or am I not seeing something here that I should be seeing?? Any help? In addition, how do you adjust the diaphram?? Is it suppose to move a little? a lot? the center screw and nut do what? make it go up or down further?? I'm not sure I understand the exact way to get the choke set up correctly. any help. Thanks.

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Old 09-22-2008, 03:37 PM
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I believe the triangle thing you are talking about is the choke pull-off. The way it works, is when your car is dead cold and your choke flap is totally shut to give maximum fuel enrichment when the car is starting, the choke pull-off is disengaged and doesn't effect anything. Once the car fires and starts, the engine pulls a vacuum on the choke pull-off which pulls open the choke a hair to allow some air in and keep the car from loading up on fuel and stalling. All this happens within a second or so and it's hard to see unless you have a remote-starter button or a patient helper.

It's a tuning device. Your car will work without it functioning, especially if your fast idle is set higher and your chokes don't close entirely. It allows you to get the lowest fast-idle without stalling on the first crank of a cold engine (which is good for engine life, you don't want her screaming when she's dead cold with extra fuel pumping in and all if you can help it)
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Last edited by todds; 09-22-2008 at 03:51 PM.
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Old 09-22-2008, 05:45 PM
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Wow, thanks. That pretty much answers it. You mean, that plunger and the heating element and all of that adjustment is not nessesary in the cars overall performance? I've got it hooked up, but I was just wanted to make sure.
In addition to that, the vacuum pot on the side of the engine where the throttle linkage is at has a canister. Is that needed? It says it's to help keep the car from dying when you let off on the gas. Mine has a piece missing, and after rebuilding them, I noticed something wasn't right on it. I'm not sure if it has to be there or not.

Since I have you here.....the secondaries ...do they open with a vacuum too? I noticed on the linkage that it doesn't move at all when I open the throttle. Prior to rebuidling, it was froze......now it moves, but only when I push it over by hand. ???? Thanks again.
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Old 09-23-2008, 02:44 PM
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The answer is yes to all your questions. The plunger/heater/springs/etc are all there just to make the choke flap stay at the proper angles when the car is warming up. Once it's warmed, the flap should be wide open and none of that stuff will effect the way it runs. The flap itself will move around a little against the pressure of the little springs in there when the engine is revving when cold, this enrichens the mixture slightly as the extra air sucks it closed. It's a complicated little dance it all does, in addition, the fast idle cam is in there too. In addition to all THAT the heat risers do their thing too.

The vac pot on the side is another tuning device which also helps in getting a nice smooth low idle without stalling. You'll find that without it, the car tends to either bang into gear or stall when going from P to D and soforth. It also helps on offramps or long decels down a hill that end in a traffic light when the engine wants to die from an overrich mixture due to all that vacuum. (This is horribly annoying - been there) The engine starts to sputter and die, loses vaccuum, and that thing kicks in. All it does is goose the throttle a little to keep things happy. I'm not sure about a reservoir canister as mine just goes straight into the side of the carb base. One side effect of this thing which I find a little weird is that it also gooses it a little when first starting on a warm engine.

The secondaries are vacuum too, you got it. They are almost pseudo-mechanical however due to that long ramp that prevents them from opening on the primary throttle. I think there may be a lockout from the choke too, so that they don't open when the engine is frigid also as a protective measure. When you're not moving fast and suddenly floor it, the secondaries take their time opening so that they don't outpace the actual needs of the engine (as measured by the heavy vacuum). When you're hauling and floor it, it almost acts like a mechanical secondary because it's more or less following that long ramp on the throttle because there's less vacuum. It's another thing that you wouldn't notice unless it wasn't working and you were getting sputtering when flooring it from low speeds or the opposite was happening and flooring it was kinda lackluster. It's all a bit harder to notice in reality due to the cars' tendencies to lurch into that stump-pulling first gear anyway. If only they came with taller gears...
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Old 09-24-2008, 12:58 PM
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Smile

Wow, Todd. This is good stuff. Thanks. You're helping a lot. I'm starting to understand more and more now. I have 2 more questions as I am done with the rebuild, but have found a few ''issues'' that I am concerned about.
First is the fuel return line. There is a flap on the bottom, that pushed that little pin up, and then there is a ......feeler gauge looking thing in the back that pushes it back down when the gas pedal moves up and down. Mine is tight. Seems to be sticky, and doesn't move a lot. How important is that for the return fuel line? Does it have to move freely? How can I get it to move?

Another issue, is the Vents on the carbs.. Hot start vents. The one spring is worn, and is bent. I don't see any way of getting it out to change, or replace it. Without it I can see where hot starts would be an issue.
Further, I'm missing that bottom spring, and long screw that goes into the vaccuum pot, so someone prior took that part off, and now it doesn't want to push that vent spring up anymore, and the adjustment is all the way out.

Do I change the entire section to fix it? Where can I just get the spring and bolt for that vac pot? I need to address these issues before I put the carbs back on the car. I want the carbs fixed correctly before I got slapping them back on.

Thanks again, for all your help. I'm starting to catch on.

Dave
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Old 09-24-2008, 05:11 PM
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You can clean the return valve but be very gentle! There is a diaphragm inside which is usually brittle. I'd suggest spraying the outside plunger with a non aggressive cleaner/lube once a week and gently pressing on the plunger. It should loosen up over time.

Have I mentioned "gently" often enough to make my point?
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Old 09-27-2008, 12:26 PM
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Ok, the car starts, and idles REALLY HIGH, AND FAST. I think the high idle screws are off. How do you adjust those? I know the gold screw is the idle mixure, and it's 1 and 1/2 turns out to start, but the high idle is inside of the heat sensor unit. Where do you start off with it? Thanks.
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Old 10-20-2008, 03:07 PM
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Put the metal shaft in a vice, and slowly twist the stainless steel round disc on the top, this should rotate the gasket so that it lines up with your old one.
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Old 10-20-2008, 03:27 PM
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Well, in reference to the fast idle screw, I basically start with mine barely holding the highest step of the cam, there are 3 or 4 steps. If that is not fast enough, turn it in little by little until it is. Another adjustment that goes hand-in-hand with the fast idle screw is the gap acquired via the choke pull-off. Once it starts, the choke pull off helps dictate the mixture. This stuff can only be set when the car is stone-cold. You can play with the choke flap with your finger to see what closing or opening it does with the car running when it is cold and first started.

Before you get into all that however, you want to warm it up to the point where none of that is even effecting it. If your car is fully warmed and the fast idle screw is still increasing your idle, you have to back it out ALOT (totally out of contact) Also, I'd make sure the vacuum dashpot to boost the idle speed isn't effecting it either. When warmed, the ONLY thing that should be dictating your idle speed should be ONE of your idle speed screws and the balance screw in the linkage. If your carb-carb balance is off that will throw everything else off, set the airflow there first.

Note that the fast idle only applies to ONE carb, (the throttle linkage keeps it open on the other) whereas the choke pull-off needs to be set on both. On the other carb the fast idle screw should be fully backed out or removed.

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Last edited by todds; 10-20-2008 at 03:34 PM.
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