choke thermostat?

[pinkfuzzibunnies]

Hi, just a quick question...is it pretty easy and straight forward to replace the choke thermostat on a 75 dodge dart? I'm pretty sure mine needs it cause it's starting to get cooler and now it's acting up, and it seems a pretty easy fix but I just want to ask so there are no surprises, cause I'm no expert with cars, just learning as things go wrong. If there is some kind of tutorial or something I could be linked to that would be great, Thank you!

 

[TrailBeast]

What carb?

 

[PocketAces]

There are several adjustments to be made that could affect cold weather driveability. I would check them all before spending money on a new choke.
The factory service manual for my 65 was excellent at explaining all the adjustments. You can also find them in a carburetor rebuild kit for you car.

The old mechanical chokes are pretty simple. Just a bimetallic spring. Unless it's all corroded, there's not much to go wrong. Yours has an electric heating element that could fail. If it did, the choke would not come off quite as fast as it warmed up so you would be running rich until the engine got fully warmed up. If that's not your symptom the problem probably lies elsewhere.

Other than adjustments, I would say the vacuum unloader is a more likely failure point. It has a rubber diaphram inside that can fail. You can check that by sucking on the hose with your mouth. It should move when you suck on the hose and it should not leak air.

If you could be more specific about how it's acting, we could give you better advice.

 

[pinkfuzzibunnies]

i believe my carb is a holley 1935 or 45? something like that.....basically now that the weathers getting cooler when I go to start in the morning it takes quite a few times to get it going and then needs a lot of warming up or it'll stall when i pull out. I checked the symptoms with a couple mechanics and saw a video on utube of an old dodge truck with same problem and it was the choke thermostat....we got the part (only 15 bucks) and it looks pretty simple, just unhook and rehook i guess....Thank you very much though

 

[2 Darts]

The other thing that will affect cold drivability is the exhaust damper on the exhaust manifold. It frequently corrodes, make sure it operates freely. Likewise, check the EGR valve. It can stick, too.

 

[BillGrissom]

Ditto on checking the vacuum "choke pull-off" or "unloader". It is at the top of the carb and its job is to pop open the choke slightly the instant the engine starts. Otherwise, you will never be able to adjust the choke properly. Best to check it with a hand vacuum pump. Otherwise, just push in the shaft and hold your finger over the little hole on the vacuum stub and see if it holds the position. If not, the rubber diaphragm is shot, which is common if someone shot it with carb cleaner. You can buy it alone.

 

[wjajr]

This sounds like a lazy choke that is not fully snapping shut when set because you live in a hot climate, and choke never has to be activated to start the engine. This normal for southern cars we used to get in North East on used car lots, and generally just requires some cleaning, and adjustment. However there can be several additional reasons for choke not reacting correctly.
1, Failure to correctly activate choke during warm weather. By not exercising choke its linkage becomes corroded, and dirty causing binding and sluggish movement.
Depress accelerator to floor release, and depress it about ¼ down, than crank over engine. Perform no pumping, this only floods the engine making for real hard starts.

2, sticking dirty and or bent linkage rods connecting thermal bi metal spring to choke butterfly.
When engine is cold (overnight) remove air cleaner, by hand fully open throttle, and observe movement of choke rods, and high idle cam. You may have to repeat this process several times for your eye to catch all the action. After moving throttle, hold open throttle a small amount, and open and hold choke with other hand while releasing throttle. This will reenact a cold start. Do not oil any pivot points in linkage as it just collects more crud which will bugger up its free action a few weeks later.

3, If choke rods move freely by hand, but don’t respond to opening throttle simulating setting choke, you need to check the bimetal spring by pushing down on choke rod feeling for spring resistance. If no resistance is felt, there may be a way to adjust tension, or the spring has most likely broken. Broken spring can be checked by unbolting the cover of the choke stove recessed in the manifold and looking at it.

4, If spring is broken, you may be able to find a replacement, or if not there are retrofit electric choke kits available to replace factory device.

If you went through all the above, and choke looks and appears to work correctly after cleaning, adjustments, and some fiddling around, it may be time for a carburetor rebuild.