stock 1973 318 V8 starts but won't idle without foot on pedal

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Lasalle

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Even after it is warmed up it will die if I take my foot off the pedal. I'm doing a lot of work on this Dart to sort it out after a 25 year storage. New spark plug wires got it running but a a trip to my modern car mechanic did not solve the startup issue. They timed it and adjusted the choke. My diagnostic skills under the hood are not good. What steps can I take to identify the problem and make this car run smoothly?
I have done some significant repairs to the front suspension and transmission with help from this forum!
 
How about the idle mixture screws? 2 1/2 turns out is a good start.
 
No I did not try that yet. That is next. I have a factory service manual. Two things I have always been scared to tinker with is a carburetor and an automatic transmission. I watched enough youtube videos to gain enough confidence to open up the trans and replace the leaking seals. I guess between you guys and youtube I will start working on the carburetor. A trip to a professional did not help. They don't want to put the time into it to get it right.
 
Even after it is warmed up it will die if I take my foot off the pedal. I'm doing a lot of work on this Dart to sort it out after a 25 year storage. New spark plug wires got it running but a a trip to my modern car mechanic did not solve the startup issue. They timed it and adjusted the choke. My diagnostic skills under the hood are not good. What steps can I take to identify the problem and make this car run smoothly?
I have done some significant repairs to the front suspension and transmission with help from this forum!
I would buy a carb rebuild kit...
But first.. spray some wd40 all around the sides of the carb to manifold gasket as well as the base to body gasket of the carburetor. Let it sit a little while..
Come back and spray the base one more time... dont make puddles but get them soaked. Any puddles just soak them with a rag. Fire it up and see if it idles now...even if only moments longer before dying. It'll show you the vac leaks at the base and carb body, verification so you'll pull the trigger on buying the kit
 
Do you have some basic tune up tools? Timing light, vacuum gauge, things like that?
 
From the information provided, my guesses are;
1) the engine is flooding, or
2) the slow-speed system is not functioning
3) the timing is horribly retarded.
If none of the above apply, then the valve timing is out.
 
If the car has been in storage for 25 yrs, might have sediment blocking the idle system.
 
In response to TT5, I have a timing light and a dwell meter/tachometer.
So far the possibilities are:
carburetor related
timing
vacuum leak
I can check on these things this weekend.
 
If you get stuck, here is the not-so simple way to diagnose this.
but first, some assumptions;
1) this is not a LeanBurn engine
2) you have done your best to find a vacuum leak, including checking the crankcase, and not found one.
3) compression is about 135psi and fairly even. see Note-2
4) you have eliminated a possible reverse polarity situation at the magnetic pick-up; see note-6
5) the exhaust system is NOT severely restricted
6) the transmission and/or Convertor is/are NOT faulty, and nearly locked up in Park. see note-5
7) that's all I can think of

Ok so lets get started;
1) Make sure the brake booster is not sucking air; pinch the booster line shut and wait a second. If the idlespeed changes and stays changed, the booster is bad, so disconnect the hose at the booster and plug the line. Make sure the PCV circuit is correctly plumbed, working, and not sucking air from a cracked hose.
2) prove the gas is CLEAR, fresh, and not contaminated.
3) remove the carb, make sure the choke is off and stays off, flip it upside down and using the curb-idle screw, adjust the Transfer Port exposure to a lil taller than wide.
4) remove the mixture screws, and give the ports a couple of short bursts of low-pressure compressed air or any aerosol-solvent, then re-install to 2.5 turns out.
5) after this; DO NOT adjust the curb-idle screw.
6) reinstall the carb, fill it with fresh gas, start it up, warm the engine up.
7) if nothing has changed, you may have to clear out the Idle-Air Bleeds. With the engine idling, look down thru the airhorn and find them. Then put one finger on each one to plug them, which should cause the rpm to noticeably slow or stall. If this happens, then the slow-speed circuits are working, but if not, see note-1.
8) with good working IABs, a blown-out low speed circuit and no air-leak found, you can now rule out the carb and fuel.
9) Defeat the Vacuum Advance, and with the engine running, grab the distributor, and pull in some timing; leave the timing light in the tool box. If the rpm goes up, you are on the right track. Stop advancing when the rpm increases to more than 750rpm. But if the rpm decreases, then retard the timing to find the highest rpm , less than 750.
10) but if there is no way that the engine will come to 750, then you will have to check the cam timing. see Note-3


Note-1
To clear the IABs; I do this by reving the engine up to about 2000, keeping it there, and slamming the choke shut until the rpm drops to 1000 or so, then still holding the throttle in the same place, I let the engine rev back up. As soon as the engine has recovered, I let it return to idle. The high vacuum created underneath the choke acts like a big vacuum cleaner sucking fuel frome everywhere, mostly the IABs tho,lol. Sometimes I have to repeat as necessary.
Note-2
As to compression; I have never seen a Smoggerteen318 with less than 120 psi on all cylinders. That doesn't mean they don't exist. But If I had one, I would yank it out for a rebuild.
So then, if you get some sadder than 120 psi, on all cylinders, you can pretty much assume that something is wrong. Most likely it would be a valve-timing issue.
Note-3
The best way to check the cam/valve timing, is take the front of the engine off and degreeing it. But there is a short-cut that you can do, to get an idea of where it's at. It's called checking split overlap.
Split overlap occurs at or near TDC but NOT on compression stroke, rather 360degrees past TDC compression. This is the time when the intake valve is just beginning to open, and the exhaust valve is almost closed. The factory 318 cam has only about 20 degrees of overlap, so finding the split is pretty easy, theoretically.
I use #6 cylinder because it's easy to get to. So put it on TDC compression and then roll it around , one full turn, accuracy is not critical. Pull the valve-cover off. The best place to do this test is right off the lifter bodies. But you can get a pretty good idea from the push rods or retainers, because there is only the 20* of overlap. That means that the intake valve begins opening just 20 degrees before the exhaust is closed. You can watch the valve-retainers, and rock the engine back and forth and find a point that you think both valves are equally open.
Now go look for the index mark on the balancer, to see where it is in relation to the TDC mark on the timing tab. Ideally it will be slightly advanced, something like 4degrees or less. . Realistically with a stretched chain, it could be 2 to 4 degrees retarded. The engine will run reasonably well, with split overlap set anywhere from 8* advanced to 4 or even 6* retarded.
If split overlap is outside this range AND the compression is very low (or very high) on all cylinders, then the first thing you will have to do is prove that the index on the balancer has not slipped, (see Note 4), and if the mark is accurate, THEN
you will have to actually dig into it.
Note-4
You prove the TDC mark by using a piston stop. Basically you just screw the stop into the sparkplug hole then rotate the crank until the piston hits it, make a fine mark on the damper, then roll the engine over the other way until the piston hits it again and make another fine mark. Halfway in between your marks is TDC.
Note-5
If you suspect the trans, just jack the car up, put it on axle-stands, start up the engine and let it idle in Neutral. If the wheels are spinning, and the engine is happy, apply the brakes and note the change in rpm as the wheels come to a stop. If it stalls something is wrong inside the trans or in the convertor. In either case, it will have to come down.
Note-6
When the polarity of the magnetic pick-up is reversed, it will drive your timing-lite crazy. It may idle fine, but with wildly fluctuating strobes. As soon as you increase the idle speed, the strobing will go crazy with missed strobes, extra strobes, and the timing mark could appear to vary wildly; and of course, the engine will run stoopid.
Note-7
If your valve seats are rusted up keeping the intake valves open, your manifold vacuum will be low. With the loss of vacuum, the engine will be down on power. and you might need to keep it running with your foot. But if this is so, then it will also be very hard to start, sluggish to rev, and probably back-firing thru the carb. Since you didn't mention this, neither did I, lol.
Ok so have fun this weekend, lol.
 
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Thank you all for the responses, particularly the long one from AJ. This weekend I will study these carefully and try them.
 
UPDATE: I got it to rough idle by changing the idle mixture screw setting. I had to back out the screws 4 1/2 - 5 turns. I checked the timing and it is at TDC like the sticker says it should be. Changing the timing did not smooth out the idle. After a push of the gas pedal, the car will cold start fine and fast idle. After fast idle it will settle into a slow rough idle. It is driveable but it has no power and it feels like I'm towing a mountain. I sprayed quick start around the intake manifold and carburetor looking for a vacuum leak but that was inconclusive.
Here are some answers to questions by some responders: This is not a lean burn system, the car does not have power brakes, the gas tank has been restored/lined by Gas Tank Renu, and we drained the gas and put new in before we started this project.
Does a 318 V8 have plastic teeth on the timing gears? Could the timing chain have slipped? The car has 99,000 miles.
I just completed a front end rebuild and I have an appointment on Thursday to have it aligned. This is a general repair shop and I will have them assess why it runs so poor. Thank you for your help in getting it running well enough to keep the appointment and get it there under its own power.
 
No I did not try that yet. That is next. I have a factory service manual. Two things I have always been scared to tinker with is a carburetor and an automatic transmission. I watched enough youtube videos to gain enough confidence to open up the trans and replace the leaking seals. I guess between you guys and youtube I will start working on the carburetor. A trip to a professional did not help. They don't want to put the time into it to get it right.
None of them do anymore. It's not a labor of love to them. They just wanna hook a plastic **** box to a computer and charge their victims out the ***...
 
UPDATE: I got it to rough idle by changing the idle mixture screw setting. I had to back out the screws 4 1/2 - 5 turns. I checked the timing and it is at TDC like the sticker says it should be. Changing the timing did not smooth out the idle. After a push of the gas pedal, the car will cold start fine and fast idle. After fast idle it will settle into a slow rough idle. It is driveable but it has no power and it feels like I'm towing a mountain. I sprayed quick start around the intake manifold and carburetor looking for a vacuum leak but that was inconclusive.
Here are some answers to questions by some responders: This is not a lean burn system, the car does not have power brakes, the gas tank has been restored/lined by Gas Tank Renu, and we drained the gas and put new in before we started this project.
Does a 318 V8 have plastic teeth on the timing gears? Could the timing chain have slipped? The car has 99,000 miles.
I just completed a front end rebuild and I have an appointment on Thursday to have it aligned. This is a general repair shop and I will have them assess why it runs so poor. Thank you for your help in getting it running well enough to keep the appointment and get it there under its own power.
I would crank about 10 ° initial timing into it and readjust the carb idle mixture and speed.
 
Is 10 degrees initial timing another way of saying 10 degrees before TDC?
 
At 4.5 to 5.0 turns out, your mixture screws are too far out, and have lost control.
The reason that your mixture screws are out so far is because the transfer slot is not providing the right amount of fuel. This can be because of; 1) incorrect curb-idle screw adjustment, or 3) incorrect 'Wet" fuel level, or 3) too tight a valve lash, or 4) because of a lack of understanding the role of Idle-Timing.
In a properly working system; The transfer and mixture screws, work together at idle, with the transfers doing the bulk of the work, and with the mixture screws just acting as trimmers. The star-player in this union is the "WET" fuel level. If the "wet" fuel level in the bowl is not what the carb designer calls for, nothing works right. You may be finding that out.
>Your idle-timing has nothing to do with making the engine run right. You can NEVER give the idling engine the amount of timing it actually wants, and still be able to drive it. It wants 25 to 30 or more degrees! at idle.
No; your idle-timing is "settled on", by the manufacturer, in order to create a balance of transfer to trimmer fuel delivery synchronization that allows the transfer slot to function properly at idle, with no tip-in sags, hesitations, nor requiring excessive pump-shot to overcome a bog.
>Your statement of;
I had to back out the screws 4 1/2 - 5 turns.
proves that your Transfers are not supplying enough fuel; normally the trimmers will be set to ~3 turns +/- .5 turn. You need to decrease the mixtures screw setting, and increase the transfer fuel, and if the idle speed is not right, change the timing until it is. If this requires excessive advance; something is wrong. Either your EFFECTIVE compression ratio is very low or your valve timing is out of whack. The principal player in these matters can be but is not limited to, the valve lash.
>To increase the transfer fuel, you have to increase the slot exposure with the curb-idle screw OR increase the height of the "wet" fuel level, or decrease the size of the IABs. If you fail to synchronize these, your ENTIRE low-speed mixture will be rich due to the fat trimmers. Your goal is to try and reduce the trimmers towards 2.5turns for best fuel economy.
>Let the idle-timing be whatever it wants to be, that makes the Power-Timing reasonably close but NOT so much as to cause detonation, which leads to broken pistons and such.
> if the engine continues to run rough, look to the cylinder pressure balance. In a good working engine, the numbers will be very similar for every hole.
 
25 years? And you got it running? The hard part is done. 4-1/2 turnd on idle screws, too much. Carb needs a good thorough cleaning. And a load of sea foam in gas tank.
Paper type egg carton, take parts off and out of carb and keep them organized. Clean and re-assemble with new parts from kit.
 
25 years? And you got it running? The hard part is done. 4-1/2 turnd on idle screws, too much. Carb needs a good thorough cleaning. And a load of sea foam in gas tank.
Paper type egg carton, take parts off and out of carb and keep them organized. Clean and re-assemble with new parts from kit.
Just a casual observer here, wanted to say I really dig the egg carton trick! Small Parts are a pain!
 
agreed, just because the timing light says it's where it 'should' be doesn't mean that's where it 'needs' to be.
Yeah well some of you need to realize the cars idled fine from the factory without the timing mods....so his should too.

Leave the **** that ain't broken alone and find the real problem.
 
Engines fired up after sitting for 25 yrs [ & a lot less than 25 yrs...] can develop a multitude of different problems. I was called to have a look/listen to an engine, similar circumstances, & a couple of valves had rusted in the guides, causing piston contact & bent valves. Engine still ran, but roughly.
 
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