Slight stumble when cold?

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71DodgeDemon340

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Hey everyone, ive noticed this winter that my 340 has developed a slight stumble or miss when the car is cold, once i drive it down the road 2-3 miles it clears up. I always let it idle for about 5 minutes or so before i drive it to allow the oil to get circulated and come up to temp. It has been about 7 years since the car has been built so maybe a carb adjust is in order? I tried i think last spring to adjust the idle air mixture and adjusted best i could with a vacuum gauge and the edelbrock manual along with help on here. It seems as though since the outside temp has been in the 50’s it seem to have the slight stumble. The stumble can be felt not really at idle just more or less with a load on the engine, almost like it surges. Its either a 650 or 700 cant remember eddy thunder series avs carb. Electric choke. Mopar chrome box. Just put new cap, rotor, plug wires and plugs in it last spring. I usually do plugs every 2 years. Change the fuel filters every year. Filter On top of the intake looks clean. Havent checked timing yet but it should still be at 16 degrees and all in at i believe 34. No vac advance. For about the first 3 miles it has a surge/ random stumble to it with a load. Not the point where you cant drive it but you can definitely feel it. It progressively goes away as i drive and by about 5-7 miles it runs great. Even did a wot pull from about 15 mph and it pulled through 1-3 no problem and you could feel the secondaries kick in and didnt hesitate at all. Just throwing me off. I dont ever recall having any stumble in the past that ive noticed. I know the ignition system is in good shape, i also keep 100% 93 in it but granted i only get to drive it about once or twice a month in the winter. Possible its bad gas? It was about 48-50 degrees out when i took it for a drive, not sure if the fuel was too cold? Any suggestions. I need to get with the engine builder and have him double check the idle air mixture and start from there. And maybe have him give the carb a good once over. I know i cant completely rule out the ignition module. I have a orange box i could swap in and try it to se if there is a change
 
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Electric choke timing is adjustable, it maybe either too fast or too slow and it may need adjust as temps change. Does you car high idle at all when cold? There is also winter gasoline that can cause some headaches. Is your 340 all stock? If all street car you should be running the vacuum advance off the timed vacuum port (i.e. the one with no vacuum at Idle)
 
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Electric choke timing is adjustable, it maybe either too fast or too slow and it may need adjust as temps change. Does you car high idle at all when cold? There is also winter gasoline that can cause some headaches. Is your 340 all stock? Id all street car you should be running the vacuum advance off the timed vacuum port (i.e. the one with no vacuum at Idle)

it usually does until you tap the throttle, i pulled it out of the garage after i started it up so i didnt pay attention but it was idling around 800. i may have made the choke come off too soon. Bored .040 over 9.5:1 comp. lunati voodoo cam. Edelbrock heads and intake.
 
Sounds like its running lean when cold. Give 'er some more choke adjust.
 
Electric choke timing is adjustable, it maybe either too fast or too slow and it may need adjust as temps change. Does you car high idle at all when cold? There is also winter gasoline that can cause some headaches. Is your 340 all stock? If all street car you should be running the vacuum advance off the timed vacuum port (i.e. the one with no vacuum at Idle)

is there any tuning that has to be with the carb or distributor when running vac advance or do you just hook it up and forget it
 
I agree with gliderider06. Sounds like it’s lean when cold. Choke should be adjusted to stay slightly shut a little longer. Or. Has the car sat awhile ? Carb could need a cleaning / rebuild. Doesn’t take long to gum one up with this terrible gas today.
Just my 02
 
I adjusted the choke to one notch richer. It was on the second notch on the rich side from midway. Midway is the factory preset. Its on the third notch on the rich side now. Weird though its been fine for years. What causes all of the sudden for it to be off?
 
I agree with gliderider06. Sounds like it’s lean when cold. Choke should be adjusted to stay slightly shut a little longer. Or. Has the car sat awhile ? Carb could need a cleaning / rebuild. Doesn’t take long to gum one up with this terrible gas today.
Just my 02

car has sat for a few weeks. Did it two weeks ago when i drove it as well. I hope its not gummed up. I try to run it at least a few times a month. Also using what is supposed to be 100% 93
 
Easy enough to pull top of carb off and take a look inside.
Wouldnt hurt to check for vacuum leaks too.
 
I adjusted the choke to one notch richer. It was on the second notch on the rich side from midway. Midway is the factory preset. Its on the third notch on the rich side now. Weird though its been fine for years. What causes all of the sudden for it to be off?

It should not change like that.
Do check for a vacuum leak or: cracked rubber hose ....
clean the throttle plates by the “throat” of the carb too.
It’s changed for some small reason.
 
Once the car is fully warmed up ( operating temp) the choke plate should be straight up and down ( fully opened )
Little bit O info.
 
If your setting timing disconnect and plug it. Your total may be a bit high a 43*

my bad i looked on older posts. Its all in is around 34. Had my numbers backwards lol. Been cutting down a few trees today and my mind is a little off lol
 
It might. Try a 3/32 or there about and see if it engages anything. Might PM TrailBeast as he could have set it up for your combo.
 
I wouldn't suggest to mess with the advance screw yet
If anything just disconnect the vacuum advance, plug it and see if the stumble goes away. If it's still there, it's not an advance issue. He could go down a slippery slope quickly and have a bigger problem to deal with.
 
I wouldn't suggest to mess with the advance screw yet
If anything just disconnect the vacuum advance, plug it and see if the stumble goes away. If it's still there, it's not an advance issue. He could go down a slippery slope quickly and have a bigger problem to deal with.

vac advance isnt hooked up
 
Start off with obvious / easy stuff.
1 Look for a vacuum leak.
2 How’s does it respond to adj the choke ?
3 what do the plugs look like ?
Don’t go crazy and create another problem.
Check , change ONE thing at a time and recheck.
It is a lean stumble when cold.
 
Start off with obvious / easy stuff.
1 Look for a vacuum leak.
2 How’s does it respond to adj the choke ?
3 what do the plugs look like ?
Don’t go crazy and create another problem.
Check , change ONE thing at a time and recheck.
It is a lean stumble when cold.

dont think its a vacuum leak, i adjusted the choke one notch richer, will see this weekend what it does
 
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