Buffalo Dude

My car has a problem when it's real cold in the morning. It stops running :cry Some guys were saying the carb might be coming off the choke too quickly so the block isn't warm enough to keep running and my problem might be a bad thermo (in the carb that is). I just had the carb rebuilt last feb and on the bill it looks like they put in a new thermo. So can the thermo fail prematurely? My car only has another 1000 or so miles since the rebuild.

'75 coupe, L48, TH400, original carb


[Modified by Buffalo Dude, 9:42 PM 12/20/2001]

rainman69

:confused: :confused:

You had the carb rebuilt and they put a new thermostat in your engine? That makes no sense. (Not being harsh on you...I'm just confused).

The easy way to tell what is happening is have two people. One starts car "normally" and the other watches what happens with the carb. That way, he/she can see the choke operation. If the choke is working right, might want to check air/fuel ratio...or see if your heat riser (passenger exhaust manifold) is messed up. It's a start. :smash:


[Modified by rainman69, 10:45 PM 12/20/2001]

Buffalo Dude

Supposedly there's a thermostat in the carb to tell it when to come off the choke. I'm looking at the bill and it says they replaced the thermo when they did the rebuild, so I'm assuming it's the carb and not the thermostat that regulates engine temp.

If I take the air filter off to watch the carb, do I have to worry about "burping" and a big engine fire? Cause not running right is a whole lot better than torched.

Thanks for you input rainman69 :chevy

Rockn-Roll

They don't really go bad. It's just a coiled spring which opens up when heated. I've seen choke springs from the 50's that still work fine. I think the problem is the adjustment screw for the fast idle located behind the choke housing acessed from the front of the carb...you probably just need to turn the screw out a turn to lower the rpms of the engine while it's warming up. There's a couple of steps on the choke idle cam that keeps the throttle cracked open the right amount to keep the rpms up while the engine is warming up, then there is a drop off for when the engine is at operating temp. There should be a choke pull-off vacuum actuated solenoid which will pull the choke open when the engine reaches the right rpms. I think maybe your engine gets to the "right rpm" too soon which causes the choke pull-off to open the choke and thus killing the engine.

Personally, I removed my choke pull-off cause it was leaking and didn't care to put another one in; but, it's usually better to install a choke pull-off cause sometimes the choke idle cam doesn't kick down so I sit at traffic lights with an 1100 rpm idle.

mrvette

I'ts been a few years, so bear with me, there are two differant types of those black 2" dia. round thermostat housings, first to appear was the type with a 1/4 inch dia tube running into the housing, from the manifold, that draws air from the air cleaner into the exhaust xover, where it is heated and then heats that thermostat spring to open up and relax the choke closing.....other one appearing later, and is common enough now, goes to +12 with a wire to heat the spring electrically, either one should work well.....
so when engine is cold, remove air cleaner and watch choke action when accelerator is pressed, or primaries opened, engine off.....
the choke should snap shut like a bear trap....and you should see/hear a good accelerator pump squirt....now hit the starter, it should fire off allmost immediately, if not, the choke is NOT closing all the way, and there are 3 screws on that black round housing to loosten and adjust/turn the black housing to close that choke further....turning the housing counter clockwise as looking at it...will put more spring pressure from the t-stat onto the choke closing linkage....
as the engine starts, vacuum is rapidly formed in the manifold and in turn actuates that 'pull off dash pot'....that pulls the top choke plate open about 3/8 inch worth on edge of butterfly flapper to carb top...roughly....
thermostat spring is still cold opviously, trying to close choke flapper, when it's HOT, the engine should be up to temp and choke opens all the way by itself and a small weight on the passenger's side....mounted in there with a sloopy type linkage....you need study that real hard to get what's happening, words can't describe it adequately....
at any rate, the cold idle speed is the screw on the DRIVER's side....on the 'fast idle cam'.....watch the choke action and it's apparent what happens....the HOT running idle speed is controlled by a well hidden screw on the Passengers' side of carb, down under all that linkage/weight area......

GENE

Gary79

it just might need an adjustment. i put a new edelbrock quad on my vette after rebuild in the summer of 2000,had a friend dial the quad in for me, and then later when it got cold out i adjusted the settings on the choke to the 1979 settings and he dialed it in, & kept it a couple of days so he could start it from dead cold in the morning and check it.

Techno

The fast idle screw adjusts the idle, do this if its too high or low.
The electric choke or mechanical choke adjustment screw adjusts the temp range it works in.- How hot the engine gets before the choke system is completely out of the picture. And depending on that how much spring pressure it supplies when cold.

The bend in the top of the choke linkage is what adjusts the choke. There is a specified distance between the carb intake and choke blade when closed. This is probably the problem. Usually they mention a number sized drill bit to set it.(every one has one of those!) When the engine starts the choke opens slightly from the start position. You can see the slop in the slot for the linkage arm for this or just wiggle the blade, its supposed to be there.
The choke should not be completely closed, at least when the engine is running.
You can start the car as previosly mentioned and with your hand on the blade or linkage close the choke more when it starts. This should keep it running. Slightly bend this arm to adjust. You probably have the electric choke, these heat up when the ignition is on. whether or not the engine is running.

If your engine back fires this would be the fire problem your thinking of. Your car can start on fire if you have fuel leaking out of the fuel line. Both are problems you should address instead of the choke.

daily_driver

thermostats can come bad outta the package.....

Larry B.

I bought a new choke coil that was put on the post BACKWARDS from Eckler's. They do go bad over time.. They come on ok but won't go off or vise versa. :crazy: