340 Charger will not stay running!!! please help!!

[Tim Chavez]

hey guys.
youtube is failing me and i can not get this damn 340 to stay running...
Heres the specs
its a 1970 J head 340
long tube headers
Edelbrock 650 with manual choke(rebuilt myself)
vac advance HEI style all in one, two wire distributor
performance ignition coil
new plugs
new wires
new oem mechanical fuel pump.

it will not even try to fire without being choked.
choked it will start firing intermittently (almost like not all cylinders are firing)
but with throttle it smooths out to sound normal (but this is around 1600-2000 rpms)
once its acting like all cylinders are firing is when i let go of the throttle and it will drop down and die immediately (again sounding like cylinders are stopping firing then dieing completly) if i hold slight throttle it will stay running longer but will eventually(about 30 seconds to a minute) it acts like its running out of fuel and will die. if you play with the throttle and keep it at high rpm, you can keep it running (and driving) but it almost always dies without at least 1/4 throttle help (sometimes with 1/4 throttle it will die).
when it dies it always puffs air back out of the carb.
so i'm lost....
do i look at timing, fuel, ignition, the carb build, Carb tune?
driving the engine sounds and feels like all 8 are firing just fine(no major vibrations and smooth engine roar)
all your help is greatly appreciated

 

[747mopar]

Sounds like a bit of ignition timing and possibly carb issues as well. Start with double checking the firing order and initial timing.. Where is your timing set? Your initial will very depending on the build but somewhere around 15-20 degrees btdc should get you close.

Where are your air screws set and did you check the float level? Needing to be choked once its warm is a sign of a lean fuel mixure. Might want to check your fuel pressure as well to rule it out.

 

[Mopars & Missiles]

Vacuum leak?

 

[Don Frelier]

Vacuum leak or a blocked low speed circuit in the carb. If it's a power brake car try plugging the line to the booster perhaps the booster leaks.

 

[Lionized]

Old/bad gas? Add a bottle of fuel stabilizer to be sure.

 

[BeepBeepRR]

Just saw that you have a manual choke. Sorry my comment was about the hot wire from an auto choke to the coil.. My bad for half reading.

 

[tonysrt]

Is this a new build or something that has just started to plague you? Has the car been running ok and just crapped out? Be patient and just go through everything carefully. I just put on 4bbl on a 318 that was running ok, but the 4bbl created a night mare, distributor plate was missing a clip so timing was all over the place and I found all the pushrods bent. Why it ran ok with the 2 bbl I'll never know. After the 4 bbl was on I thought I had a manifold leak so took it off and that's when I found all the problems. I had just bought the car so really didn't know the history of it.

 

[PP1RT]

Vacuum leak. Choking it gives more fuel less air. More throttle helps but engine has to be running lean. Disconnect and plug off any and all vacuum accessories. If that doesn't change anything spray carb cleaner around the intake gasket and carb base areas and see if the rpm changes.

 

[burntorng70]

I went through something just like this with mine over the summer. I had a blown diaphragm in my vacuum advance , you have a vacuum leak somewhere.

 

[Z-Man]

I had a cracked coil on a 383. It would start and run great for 30 seconds then die. Just a thought.

 

[scot]

If it runs with the choke engaged it is not getting enough fuel = vacuum leak/not enough fuel per air intake. Are you sure all the vacuum ports are plugged on the base of the carb and on the intake manifold ?

 

[Bill Monk]

Leaning toward vacuum leak as well

 

[Tim Chavez]

all ports are plugged with rubber hose caps except one, the power brake vac port. i do not have power brakes and it is plugged with a bolt. i have sprayed the whole intake with carb cleaner no change but its also around 1500 rpms when doing this

the engine is not a new build. it was swapped in by the previous owners father more than 15 years ago. i purchased the car from the son(15 years ago as a teen only to not work on it for 14 years haha) to help with legal fees, he didn't know really anything about what was done to the car by his dad(didnt actually know it was a swapped in 340 not a 318 that was stock) so we will call it unknown 340, i researched every number i could find and it appears that the block and heads likely came from the same car (1970 340 duster) the trans is a 1972 727 tf from stl plant but i do not know what he may have done internally. rear end is also not stock, its a suregrip but not sure of what gear ratio it is.

ive been chasing the running issue ever since i started working on the car. there has only been two times that i have had it warm and running well enough to close the hood and drive. ( still over 1000 rpms and without a cleaner)
this is why i rebuilt the carb, replaced the distributor and replaced the coil. I'm fairly certain that i was able to keep the timing at TDC but i do not own a timing light to really verify. i know the firing order is correct. it unfortunately has a major exhaust leak and this is causing alot of extra noise when chasing why its running poorly. the good news is i have the new headers the passenger side is in the drivers side will be going in this weekend. and hopefully i can figure out the running issue.

 

[Don Frelier]

When you did drive it was it pretty sluggish?
Assuming the carb is close, (about 2 turns out on the idle screws to start) and you have good gas.
Advance/Check the timing. You can turn it over manually until it's 15 degrees before the TDC zero mark. Take a sharpie and mark the distributor housing right where the #1 tower on the cap is. Then rotate the distributor so the rotor is in line with the post for cylinder #1. If the dist is not on #1, then one more rotation on the crankshaft because it's a 4 cycle (2 crank rotations = 1 distributor rotation)
It should start better, if the starter labors when warm then it's advanced too far.
I would look for a used light, they are cheap I have a couple.
If it still does not run it's possible that the timing chain has jumped a tooth.

 

[Don Frelier]

If you find that you need to advance the distributor even more to get it to start and idle (like 30 degrees).
Then almost certainly the timing chain has jumped. It will have very little power until you get to higher RPM.

 

[Tim Chavez]

As far as running sluggish im a bbit ignorant. It seems to wrap the tach without bogs or stutters. It feels like it has power but feels is reletive considering my daily driver is a 2015 nissan(my company car) and a 96 cummins rhats stock... a pissed off gokart "feels fast" to me haba

 

[Tim Chavez]

Also i dont know if ive said this yet but fuel tank filter and pump are new. Lines are old but gas is new

 

[burntorng70]

With the edelbrock carb the rods will pop up if vacuum is weak. Loosen the retainers and swing them out to just hold them in. If they are fluttering or staying up you might try a weaker spring. Also if you push them down and it runs you know you have a vacuum problem. A Cam that is too big to create good vacuum at idle also will cause this with that carburetor.

 

[PP1RT]

No timing light is not the end of the world. Loosen the hold down bolt for the dist just enough so you can turn it. Have a buddy try to start the car while you turn the distributor a couple degrees at a time. Mark your starting point so you can come back to it again if there is no change.

 

[BeeKool]

Just reading the part about how it won't start w/o being choked says that it's not getting enough fuel.
Will it stay running if choked?

 

[747mopar]

You saying that it sat that long really has me questioning the carb, sitting that long would likely wreak havoc on the carb if it had any fuel in it. I know you said you rebuilt it but did you shoot carb cleaner threw every orfice, port and jet watching to make certain they weren't blocked?

Do you have a buddy with a known good carb you could borrow? Bolting one that you know works great would be an easy test to try.