Do I need a choke?

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DemonSwede

DemonSwede

Active Member
Joined
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Stockholm Sweden
Hey guys! After having installed a new intake (RPM AirGap) this winter my 340 is really difficult to start when cold. It’s an almost stock engine but slightly cammed. It has a Holley 750 DP without choke on it now and I’ve never had any issues doing cold starts before I changed the intake. Now I need to crank it for like 30 secs for it to start and it runs really poorly until it warms up. Once warm it starts and runs good! It has the stock mopar electronic ignition with the blue box.

Do you think the new intake requires a choked carb? If so, would I be better of getting a new carb or try to retrofit a choke to my existing carb?

I’m also thinking of upgrading the ignition this winter to a HEI or other digital setup, do you think an ignition upgrade would help solve the cold start issue without adding a choke?

Thanks!

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DemonSwede said:
Hey guys! After having installed a new intake (RPM AirGap) this winter my 340 is really difficult to start when cold. It’s an almost stock engine but slightly cammed. It has a Holley 750 DP without choke on it now and I’ve never had any issues doing cold starts before I changed the intake. Now I need to crank it for like 30 secs for it to start and it runs really poorly until it warms up. Once warm it starts and runs good! It has the stock mopar electronic ignition with the blue box.

Do you think the new intake requires a choked carb? If so, would I be better of getting a new carb or try to retrofit a choke to my existing carb?

I’m also thinking of upgrading the ignition this winter to a HEI or other digital setup, do you think an ignition upgrade would help solve the cold start issue without adding a choke?

Thanks!

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Did you make any other changes when you installed the new intake? Just changing the intake should not cause this. When the engine is dead cold, look into the carb as you are opening and closing the throttle. Do you see a steady stream of fuel? Did you set the timing back to where you started before changing the intake?
 
DemonSwede said:
Hey guys! After having installed a new intake (RPM AirGap) this winter my 340 is really difficult to start when cold. It’s an almost stock engine but slightly cammed. It has a Holley 750 DP without choke on it now and I’ve never had any issues doing cold starts before I changed the intake. Now I need to crank it for like 30 secs for it to start and it runs really poorly until it warms up. Once warm it starts and runs good! It has the stock mopar electronic ignition with the blue box.

Do you think the new intake requires a choked carb? If so, would I be better of getting a new carb or try to retrofit a choke to my existing carb?

I’m also thinking of upgrading the ignition this winter to a HEI or other digital setup, do you think an ignition upgrade would help solve the cold start issue without adding a choke?

Thanks!

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If it's hard to start when cold you could use a choke. It looks like everything has been removed and if it wasn't you that did that you will either be searching for parts or getting a new carb. Or just put up with what you have. Your call.
 
Ricks70Duster340 said:
Did you make any other changes when you installed the new intake? Just changing the intake should not cause this. When the engine is dead cold, look into the carb as you are opening and closing the throttle. Do you see a steady stream of fuel? Did you set the timing back to where you started before changing the intake?
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Not really, I had the heads of and replaced the head gaskets but nothing else that would have any impact on this. I've been playing with the timing ever since getting the car but now it's at around 18 degrees initial. I've had som issues with the vaccum advance as I'm only getting about 10hg of vaccum at idle due to the "choppy" cam. I've tried to adjust the membrane but that doesn't seem to help and I'm quite sure it doesn't do anything at idle. I actually have the vaccum advance plugged right now as that seems to be what it likes best, runs great that way (when warm). Still gets about 35-40 degrees of timing at around 3500 rpms. The uncertainty around my vaccum advance setup is why I'm considering changing my ignition setup, I just don't feel confident with the current setup (which I didn't put in the car).
 
I see a couple things wrong, Get a shorter throttle spring. That one is too long. I hope you have a 4 speed.
 
Airgap intake… yes you will need a choke or deal with rough start until it warms up. When you make modifications away from factory you have to expect different results. Also your distributor looks a tad advanced. Off a tooth on the drive ? Maybe the picture angle is throwing me off.
 
Not being there when its being started makes it hard to make any absolute statement.
If it runs well warmed up, then the tune is ballpark correct and a choke would help with start.
To run a car without choke usually requires adding some fuel before turning the key (extra pump shots) and then finessing the throttle as the engine fires and bringing the rpms up to 1800-2000 with the throttle.

Vacuum advance is for leaner conditions and while some use it as a workaround at idle rpm, normally it does not come into play at idle. That's getting off topic, but knowing the rpm of the 18* initial IS important and may be relevant to starting.
 
toolmanmike said:
I see a couple things wrong, Get a shorter throttle spring. That one is too long. I hope you have a 4 speed.
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Sharp eyes this morning.
That's a safety as well as a performance move.
Then adjust the throttle cable for full movement of the throttle.
 
I don't see a throttle plate. Is it a bad picture, my bad eyes or is it actually missing the throttle plate? How does it even run properly let alone start without that?
 
I ran a 700 double pumper with no choke on the 340 in my '65 Barracuda for about 40 years. Starting procedure was to simultaneously turn the key while giving the throttle a few pumps, thus effectively using the accelerator pumps to richen the mixture in the absence of a choke. Your air gap manifold will probably make a little difference in cold weather warmup compared to my Edelbrock LD 340, but starting a cold engine shouldn't be any different. I had the Direct Connection blue box ignition on mine, but a more contemporary setup might give you that little edge in a stronger spark that would help with the poor fuel atomization in cold conditions.
 
69cudaownr said:
I don't see a throttle plate. Is it a bad picture, my bad eyes or is it actually missing the throttle plate? How does it even run properly let alone start without that?
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You mean a choke plate
 
To further elaborate:
There are three stages to most automatic chokes.
1. Initial choke with cold engine. This is the closed choke plate position for starting a cold engine. It will also link to a fast idle throttle position.
2. Qualified or cold running just after starting. As soon as the engine starts running, there should be enough manifold vacuum to pull the choke further open. The diaphram to do this may be visible or inside the choke.
3. Transition to warm running. As the engine warms the bimetal spring moves the choke plate further open. Slower idle is achieved through a link, and usually requires kicking the throttle to release the fast idle cam.
 
toolmanmike said:
You mean a choke plate
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Got it. I’ve never seen that removed. I figured he meant there was no choke cable/linkage.
I guess when you live in southern states you probably would never need the plate.
But, I would think it would be beneficial in Stockholm unless he doesn’t drive it November - April.
 
choke or no choke 30 seconds is crazy
2 or 3 pumps of the primary squirter it should start in 2 seconds no choke even@45 degrees out dead cold
hold it at 2k for 3 min maybe a little longer with the air gap it should idle
10 inches of vacuum is pretty big cam in a stocker if installed right
might want more initial timming
whats your cranking compression ?
 
Just a simple observation.

If you had the OEM manifold it has the cross over port that might have had just enough heat to allow good running without a choke.

I live in northern CO and even on 10 deg days my stock 273 2bbl will start and run well (stock crossover but missing the thermostat spring and stock choke)
 
Not enough ignition timing and too lean a mixture are two things that can cause to be unduly cold natured. If it started well before, I would double check the initial timing.
 
Thanks all, amazing response as always here! To comment on a few observations;
  • I too find it strange that someone had removed the choke assembly altogether, we sure don’t get enough warm weather here in Stockholm!
  • Yes I do have a 4 speed but I will definitely check the throttle linkage
  • I haven’t removed the distributor myself, only played with the timing. But as it runs good and pulls strong when warmed up I don’t believe it’s off in relation to the cam.
  • I’ve tried to give it more initial and tune it to maximum vacuum and it runs good also with about 22 degrees initial, but I’m afraid that will give it too much total as I don’t really trust my distributor and the curve
How much do you think going to a digital ignition setup (possibly hotter spark?) would impact this? If I were to go for a choke setup, would you say go for an electric or manual?
 
DemonSwede said:
How much do you think going to a digital ignition setup (possibly hotter spark?) would impact this? If I were to go for a choke setup, would you say go for an electric or manual?
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I certainly would not be concerned about a different ignition for "hotter spark". It won't help your lack of a choke.
 
DemonSwede said:
How much do you think going to a digital ignition setup (possibly hotter spark?) would impact this? If I were to go for a choke setup, would you say go for an electric or manual?
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Absolutely zero. You need to DIAGNOSE the problem first. Fix it. Then throw money at it if you still want to. Throwing money at something FIRST rarely results in success.
 
Only thing I would suggest with timing is to actually measure it from as slow as the engine will run to as fast as you feel comfortable.
You will need a 'dial back' timing light or timing tape, a tachometer, and pencil and paper.
Otherwsie you and we are all just guessing.
 
Post #13. Backing down the initial because it gives too much total is the WRONG move. The RIGHT move is to give the engine the correct timing at idle [ which you found was 22* ] & modify the dist curve.
I have been through this in the last few days with a big cammed 440. It idles best with 45*. Trick Flow heads, 10.5 CR, no idea what they need for WOT, but set up for 34*. Initial is 26*, dist curve adds 8*, vac adv connected to manifold vac adds 19* at idle. 13.5" of vac @ 1000-1100 rpm.
 
Seeing you’re in the upper 60’s F during the day, at best this time of year, it’s a bit chilly at sunrise or at night and a choke would be an advantage.

The air gap is a cold running intake and during my old winters in New York when temps got I to the low 40’s F, a choke would warm up the engine but once I started driving, the choke would come back on. A hot air feed through a OEM or like air cleaner will help a lot here. You can fab up a choke stove off of a header tube.
 
I would say that a choke would absolutely help. No question. In my opinion, when it gets cold, you will have a lot of trouble starting it and keeping it running otherwise.
 
RustyRatRod said:
Absolutely zero. You need to DIAGNOSE the problem first. Fix it. Then throw money at it if you still want to. Throwing money at something FIRST rarely results in success.
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And when you were selling parts, how many times did a customer bring back a carburetor or some electrical part complaining that it was faulty, and they wanted their money back. I worked ar a Western Auto for five years after I got out of the Air Force. Occasionally a customer would be honest and admit that the part just did not fix the problem. I would guess that 20% of the carburetors we sold came back.
 
harrisonm said:
And when you were selling parts, how many times did a customer bring back a carburetor or some electrical part complaining that it was faulty, and they wanted their money back. I worked ar a Western Auto for five years after I got out of the Air Force. Occasionally a customer would be honest and admit that the part just did not fix the problem. I would guess that 20% of the carburetors we sold came back.
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Holley used to have a HUGE return rate just because of this very problem. People just don't know how to properly install and adjust them. Western Auto. I miss that place. Those were the days man.
 
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