318 missing and stalling once warmed up and at cruise

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Jason Maitland

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Hi guys, I'm running a fairly stock and fresh 318 with Holley DP650, Auto 904, Mopar elec IGN...
I recently purchased the car (68 Dart Coupe), and all was well except for a vacuum leak, that I thought was the shaft in the Carb, so I sent it out for a full recondition with the most reputable shop here in Melbourne, Australia. Until I had the Carb overhauled, I did not have the issue I am posting about...
Since receiving the overhauled Carb, I still have a vacuum/ air leak - whistle issue at idle...
However, the issue I'm posting about for now, only presents itself once the car is properly warmed up, i.e. at least 15/20 minutes of varied driving, and perhaps after I've turned it off an back on. For instance, just now I've returned from the gas station (a 10min drive from my place) after filling with fuel, I then fired her back up and drove off fine, then after a minute or two the problem had returned. Prior to this trip I had replaced the following, as a mechanic told me I had an electrical problem, NOT fuel issue...NEW ECU Module, Coil and plugs as my suspicion was that my ecu module had gone bad, and thus was failing once it got hot...
Anyways, swapping out these items has not alleviated the problem... being that, once warmed up the car develops a bad miss/stumble whilst coasting/cruising/holding throttle steady, which goes away smoothes out completely under steady/hard acceleration. I find it weird that there's no stumble/miss under load/brisk acceleration, and also that I did not have this issue until I bolted up the freshly overhauled Carb..., Also weird, that IF it is electrical, and not fuel related WHY does it happen once the vehicle is hot?! But I'm sure you guys will know some culprits I can assess!! The mechanic who assessed it said I probably also need to bump up the timing - Could timing alone be causing my issue? Tomorrow morning I was going to maybe advance the timing slightly, and perhaps replace the Ballast Resisitor, as I bought one, but didn't bother replacing it yet. To be able to drive the car once the issue starts, I have to hold the throttle down 2/3, to 3/4 so that it doesn't stall on me, and work my 2 foot magic on the brake. I'm obviously a bit frustrated at this point and welcome any feedback, thanks:)
 
Check the reluctor gap in the distributor... .007" with a brass feeler gauge between the rib and the pick up....
 
Check the reluctor gap in the distributor... .007" with a brass feeler gauge between the rib and the pick up....
Would this gap , if incorrect, only cause a problem once the engine is warmed up, and only whilst coasting/idling, and NOT under load?... If so, are you able to show me a pic of the actual parts you are referring to? I can check with a feeler gauge in the morning!
 
“I did not have this issue until I bolted up the freshly overhauled Carb.”


Sounds like the Idle Circuit is clogged.
 
“I did not have this issue until I bolted up the freshly overhauled Carb.”


Sounds like the Idle Circuit is clogged.
Hmmmm interesting you say... When this problem first arose last week, I stumbled into the driveway of my transmission guys place, and he kindly "attended" to it for me... First he simply revved it up and adjusted the idleto see if that would clear it, but it didn't ..so then he revved it hard, whilst manually closing the choke flap to clear out any blockage, and cracked the primary metering block to drain out some fuel, I subsequently swapped out the filter too... But the problem is back. What would you recommend I do to clear out the circuit apart from tearing down the entire carb?
 
I am betting a pick up coil. Next time it stalls check for spark right away if it has it then go fuel.
 
I am betting a pick up coil. Next time it stalls check for spark right away if it has it then go fuel.
Sorry... I should have stated, When it stalls, I can start it right away... So long as I have the throttle pressed to the floor... So, I assume this means I have plenty reliable spark ?
 
Usually any whistle of a vacuum leak is almost always the carburetor base plate gasket. What base plate gasket and what manifold? A vacuum leak can also make them do screw things with driveability like you describe.
 
Usually any whistle of a vacuum leak is almost always the carburetor base plate gasket. What base plate gasket and what manifold? A vacuum leak can also make them do screw things with driveability like you describe.
It is running an Edelbrock performer manifold, with 1inch spacer... I and others have thoroughly tested the base plate area several times for the air leakage and no luck... I think (maybe incorrectly) that the air leak is still happening through via the throttle shaft, as when I move the shaft itself I can alter the pitch of the whistle... (Of course the Carby specialist is saying I'm wrong )...
 
It is running an Edelbrock performer manifold, with 1inch spacer... I and others have thoroughly tested the base plate area several times for the air leakage and no luck... I think (maybe incorrectly) that the air leak is still happening through via the throttle shaft, as when I move the shaft itself I can alter the pitch of the whistle... (Of course the Carby specialist is saying I'm wrong )...
Ok, we're getting somewhere. So you have a spreadbore intake with a square bore carburetor, right?
 
Sorry... I actually can't 100% recall the intake spec, but from memory they are both square bore... Interested to know where you're heading with this though!?!
The standard Edelbrock performer is a spread bore intake. There's no need for that 1" spacer. They are almost always a point of contention for vacuum leaks. This is all you need. Edelbrock 2732 Edelbrock Carburetor Adapters | Summit Racing
It seals around the outside of the secondary barrels properly. That may or may not be the issue you have, but I sure wouldn't be running a spacer like that when it's not needed.
 
The standard Edelbrock performer is a spread bore intake. There's no need for that 1" spacer. They are almost always a point of contention for vacuum leaks. This is all you need. Edelbrock 2732 Edelbrock Carburetor Adapters | Summit Racing
It seals around the outside of the secondary barrels properly. That may or may not be the issue you have, but I sure wouldn't be running a spacer like that when it's not needed.
Okay I'll look into that... I have tried on many occasions to test for any air leaks by spraying around the base /spacer etc and no evidence of any leaks around there
 
When it starts to act up, partially close the choke. Does the engine speed increase or decrease when you do that? Also if it’s a fuel problem, it will show up on the plugs. Have you pulled one to have a look?
 
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Hi guys, I'm running a fairly stock and fresh 318 with Holley DP650, Auto 904, Mopar elec IGN...
I recently purchased the car (68 Dart Coupe), and all was well except for a vacuum leak, that I thought was the shaft in the Carb, so I sent it out for a full recondition with the most reputable shop here in Melbourne, Australia. Until I had the Carb overhauled, I did not have the issue I am posting about...
Since receiving the overhauled Carb, I still have a vacuum/ air leak - whistle issue at idle...
However, the issue I'm posting about for now, only presents itself once the car is properly warmed up, i.e. at least 15/20 minutes of varied driving, and perhaps after I've turned it off an back on. For instance, just now I've returned from the gas station (a 10min drive from my place) after filling with fuel, I then fired her back up and drove off fine, then after a minute or two the problem had returned. Prior to this trip I had replaced the following, as a mechanic told me I had an electrical problem, NOT fuel issue...NEW ECU Module, Coil and plugs as my suspicion was that my ecu module had gone bad, and thus was failing once it got hot...
Anyways, swapping out these items has not alleviated the problem... being that, once warmed up the car develops a bad miss/stumble whilst coasting/cruising/holding throttle steady, which goes away smoothes out completely under steady/hard acceleration. I find it weird that there's no stumble/miss under load/brisk acceleration, and also that I did not have this issue until I bolted up the freshly overhauled Carb..., Also weird, that IF it is electrical, and not fuel related WHY does it happen once the vehicle is hot?! But I'm sure you guys will know some culprits I can assess!! The mechanic who assessed it said I probably also need to bump up the timing - Could timing alone be causing my issue? Tomorrow morning I was going to maybe advance the timing slightly, and perhaps replace the Ballast Resisitor, as I bought one, but didn't bother replacing it yet. To be able to drive the car once the issue starts, I have to hold the throttle down 2/3, to 3/4 so that it doesn't stall on me, and work my 2 foot magic on the brake. I'm obviously a bit frustrated at this point and welcome any feedback, thanks:)
You say that it happens once the vehicle is warmed up makes me think that your coil is going bad. Pull the coil wire off and see if there's oil coming out, also if the bottom of the coil is half moon shaped it's going bad, now you can not have either of these 2 issues and the coil can still be going bad. The resistor could be going bad as well. The pickup in the distributor could be going bad. I would check out the other 2 possibilities.
 
You say that it happens once the vehicle is warmed up makes me think that your coil is going bad. Pull the coil wire off and see if there's oil coming out, also if the bottom of the coil is half moon shaped it's going bad, now you can not have either of these 2 issues and the coil can still be going bad. The resistor could be going bad as well. The pickup in the distributor could be going bad. I would check out the other 2 possibilities.
Coil was changed ..new!
 
When it starts to act up, partially close the choke. Does the engine speed increase or decrease when you do that? Also if it’s a fuel problem, it will show up on the plugs. Have you pulled one to have a look?
I've been monitoring the plugs... Sometimes they look great, other times rich... The fresh plugs I just put in seem to look okay, however I will pull them , take a pic and share here for some seasoned advice!
 
I've been monitoring the plugs... Sometimes they look great, other times rich... The fresh plugs I just put in seem to look okay, however I will pull them , take a pic and share here for some seasoned advice!

If they look rich when it runs like crap look the needle and seat. Probably trash in it. Or have a look at float level.
 
If they look rich when it runs like crap look the needle and seat. Probably trash in it. Or have a look at float level.
Funny thing, last night when the issue presented itself again with a vengeance, once I stumbled home, I pulled 1 plug and it looked good... Even the old plugs I just replaced looked good when I pulled them... Very frustrating!
 
With the engine running (and acting up even if you have to have someone else run the throttle) take the air cleaner off and look down the throttle bores. See any fuel dripping?
 
I think I already checked this and there wasn't, but I can fire it up, get it hot so the issue develops and have another look... Would such a problem only develop though once the engine warms up? Also, the carb has just been freshly, professionally rebuilt (doesn't mean we might not have contaminated afterwards as my friend took one of the jets out to have a look etc
 
Keep in the back of your mind now......new doesn't always mean good. It's probably not the new coil, but don't rule it completely out.
I hear ya... But the exact same issue presents itself at the exact same time after warm up... And I bought a decent MSD coil... Didn't cheap out, so I'd have to be pretty unlucky I'd think...
 
I hear ya... But the exact same issue presents itself at the exact same time after warm up... And I bought a decent MSD coil... Didn't cheap out, so I'd have to be pretty unlucky I'd think...
Not as unlucky as you might think since MSD is made in China now. Still, I wouldn't consider it a prime suspect.
 
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