318 hesitation when cold

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72Plymouth

72Plymouth

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I fixed the vacuum choke a couple weeks ago and now it idles fine when first started when cold. It used to idle very rough. The current problem is that the motor momentarily bogs down a little when giving it gas to accelerate. Then the rpms will kick back up and accelerates. During the first 5-10 minutes of driving it will continue to do this and has died once. The other day it almost died again so I quickly let off the gas and it returned to a normal idle. After the motor is completely warmed up it does't do this anymore.

Can this be the choke plate being stuck open too far or not enough?

Thanks for any input
 
Sounds like nature of the beast to me. The vacuum choke pull gives you only the initial air gap. From there he choke opens compltely over a warm up period of 5 to 10 minutes. If there is a secondary choke kick in the throttle design it will be at nearly wide open throttle.
 
whats your initial timing set at?ive had a few 318 cars and they called out for timing to be at TDC,and they run like crap there.try advancing your timing a little.that seems to help.also check that you accelerator pump is working.
 
I think it is almost wide open but I will double check and take a picture when I first start it to see where the plate is at.

As for the timing, my fender sticker says TDC but I advanced it a while back so it was at about 4-5 degrees BTDC. I'll double check it.

I've been wanting to adjust the carb and haven't gotten to that yet. When I got the car there was a box in the trunk with what looks to be a reman carb, a rebuild kit, a float, and some other parts. So I have no idea if the clean looking carb is ready to use or is missing anything.
 
When the car is cold, the butterfly valve should be nearly shut. Sounds like you need to adjust your choke.
 
Here is a photo of the choke when the car is cold started.

Here's what it does. When I give it a quick rev, the choke plate almost closes, and the engine sounds like it stops for a split second. Then the choke plate opens back up and it idles normally again. After doing this several times, it looked like the choke plate opened up a tad more, and then it stayed and didn't close anymore when giving it quick revs. What could this be?

choke.jpg
 
Normal. When the engine is cold, the bimetallic spring strip in the choke thermostat will try to close the choke. Once the engine starts, the choke pull-off will fight this and hold the choke most of the way open. This is connected to manifold vacuum. If you suddenly open the throttle, manifold vacuum will drop to zero, and the choke pull-of will relax allowing the choke plate to close a little (air flow will keep it from closing completely, it'll just swing loose). Now, as the engine warms up exhaust is heating the choke thermostat in the manifold, causing it to stop trying to close the choke. So, after the engine has run for 2-3 minutes the choke should be vertical and stay there until it has cooled off for several hours.

To verify this, with the engine stone cold, not running, if you press the gas pedal to the floor (or open the throttle by hand) the choke plate should close completely, and the fast idle screw should be on the highest step of the cam. Now if you crank the engine it should start and the choke pull-off dashpot should open the choke most of the way. If you tap the throttle the fast idle cam should drop until the screw is on the lowest step (1100-1500 RPM). A factory service manual, or the instructions in a carb kit will show you how to set and adjust the choke and pull-off. If it needs to be adjusted, it's because somebody monkeyed with it.

You do have the air hose between the divers side exhaust manifold and the air cleaner snorkel right? Also make sure the flapper in the snorkel is closing when the engine is cold.
 
C130 Chief said:
Normal. When the engine is cold, the bimetallic spring strip in the choke thermostat will try to close the choke. Once the engine starts, the choke pull-off will fight this and hold the choke most of the way open. This is connected to manifold vacuum. If you suddenly open the throttle, manifold vacuum will drop to zero, and the choke pull-of will relax allowing the choke plate to close a little (air flow will keep it from closing completely, it'll just swing loose). Now, as the engine warms up exhaust is heating the choke thermostat in the manifold, causing it to stop trying to close the choke. So, after the engine has run for 2-3 minutes the choke should be vertical and stay there until it has cooled off for several hours.

To verify this, with the engine stone cold, not running, if you press the gas pedal to the floor (or open the throttle by hand) the choke plate should close completely, and the fast idle screw should be on the highest step of the cam. Now if you crank the engine it should start and the choke pull-off dashpot should open the choke most of the way. If you tap the throttle the fast idle cam should drop until the screw is on the lowest step (1100-1500 RPM). A factory service manual, or the instructions in a carb kit will show you how to set and adjust the choke and pull-off. If it needs to be adjusted, it's because somebody monkeyed with it.

You do have the air hose between the divers side exhaust manifold and the air cleaner snorkel right? Also make sure the flapper in the snorkel is closing when the engine is cold.
Click to expand...


Thanks for the info. Nope, it was never there when I got the car. There is just the hole for it under the snorkel and on the manifold.
 
You might be surprised how much that little hose helps on a stock 318. Worth the 5 bucks to find out.
 
Ok just got the replacement carb pre heater hose. Just need to connect it. I noticed a vacuum line was missing from the air cleaner. Did you happen to know where this goes. There are a few vacuum lines plugged on the carb and on the manifold. What would go to these?

vacuum1.jpg


vacuum2.jpg


vacuum3.jpg
 
You need a manifold vacuum line to the nipple on the base of the air cleaner to activate the hot air door. Look for a plugged vacuum nipple near the bottom of the carb. Also, the long vacuum nipple on the right side of the carb by the choke linkage should be connected directly to the vacuum advance on your distributor (worth a few MPG). As for the plugged bowl vent on the top of the carb, I would just leave that open unless you still have the charcoal canister to connect that to.
 
Thanks again. Ok, I'm pretty sure that the vacuum advance is actually connected to a vacuum line behind the carb near the bottom.

So is this the one where the vacuum to the air cleaner should be instead or does it not matter much? And then the small that is plugged near the choke should be a line to the distributor advance?
 
It runs better and warms up a lot faster now. I hooked up the carb pre heater hose and the missing vacuum line. Thanks for all the help everyone
 
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