318 Idle issues

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67Dart440GT

67Dart440GT

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Hey everyone, I have been working on a little project for awhile now and have been running into some idle quality issues.

Here is what I have.

1970 318 with a 4 inch crank
Holley 670 Avenger Carb
Mopar distributor and electronic ignition
Edelbrock performer intake
Crane gold adjustable rockers
Comp XE268 cam

I pulled this engine this spring due to some seal leaks and just over all appearance issues. Noted in my "restoration" thread, I found many issues from the previous owner. After correcting all of them or most of them I am left with this idle issue.

Basically what happens is the engine shakes pretty badly when I first started it. I have corrected a lot of the shaking with timing (16 BTDC) and the idle mixture screws (2).

I have the idle set at about 700 RPM

I have worked with Rob @RustyRatRod on this for a few days and we have gotten it close but to me something still seams incorrect.

I let the engine warm up, set timing to 16 BTDC (seems to be it's happy spot)

Set the idle mixture screws with a vacuum gauge.... (slight adjustments initially make the engine really shake, then it settles down) These adjustments seem very sensitive and affect the shaking a lot.

Setting the mixture screws with a vacuum gauge really seems to have very little affect on the amount of vacuum produced. I am getting around 13-15 on the gauge and it bounces between the two.

Initially we thought this was some sort of vacuum leak so I checked all of the hoses, disconnected all of the vacuum lines from the carb and plugged them. This has no affect on the idle quality so I feel like I can eliminate those issues other than maybe the pcv?

I have taken the intake manifold off (edelbrock performer) and resealed it with new printo seals (previously had the metal stamped seals)

New carb to intake gasket.

I checked the bottom of the carb with a straight edge to make sure it wasn't warped.

I have sprayed water around the intake and carb, also brake cleaner with no noticeable vacuum leaks.

Motor mounts are tight and do not appear to be broken.

One thing I have noticed also is I can cover the primaries completely with my hand and the engine continues to run. I can close the choke almost fully with little to no affect on the engine running. Once fully close it does kill the engine.

I have uploaded a video to show the shaking.

Let me know if anyone has any ideas on what to look for.

Thanks!
 
Looks like it is firing and running evenly.

That shake looks like an out of balance situation to me.

Rotating assy re-balanced with the stroke crank?

Aftermarket pistons?

Thinking it has something to do with the crank being out of balance.

Seen the same type of thing with an external balance 360 on a neutral balance 904.

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67Dart440GT said:
Click to expand...

It doesn't sound too bad. It has a little shudder. My guess is ignition but that is just a guess. Look around for a shop that has a scope and knows how to use it. They will figure it out.
 
George Jets said:
Looks like it is firing and running evenly.

That shake looks like an out of balance situation to me.

Rotating assy re-balanced with the stroke crank?

Aftermarket pistons?

Thinking it has something to do with the crank being out of balance.

Seen the same type of thing with an external balance 360 on a neutral balance 904.

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This was my next thought. I have another balancer I was considering swapping out. I took this one off to clean and paint everything.
 
If you can cover the primary bores and/or close the choke with no/little effect then it’s running on air from somewhere. Either the secondaries are open or it has a vacuum leak. Period. Pull carb off, turn it upside down and close the secondaries down tight, but not sticking. Then re tune the primaries.
 
Don't know if you like experimenting?

Could tap on a 2 oz. lead wheel weight on the crank belt pulley starting at TDC.

Run it with the belt off, see if the shake gets better or worse.

Then move the weight 90° and try again better or worse.

180° then 270° etc.

If the engine smooths out at one of the positions, you may be on to something with the balance problem.

Fun to try:

Screenshot_20230807-195151_Gallery.jpg


Screenshot_20230807-200342_Gallery.jpg


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Here are stock 318 balancer pictures to compare your balancer to, to see that it has not slipped, and is the proper style.

20230723_220333.jpg


20230723_220349.jpg


20230723_220522.jpg


Notice the position of the crank keyway and the TDC positioning.

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I have seen this several times and Agree with Rusty's assessment, that she is sucking air. Number one clue is that you can cover the Primaries, with no change.
For this post, I'm gonna assume the shake is NOT a wrong/faulty balance.
The following is what I would do;
1) The first thing I would do is a Compression test. Not because I much care about the actual numbers, but rather, I want to know the difference between the highest and the lowest. This is just to establish a baseline and prove all Eight cylinders are working correctly. Once I get a satisfactory baseline;
2) I would Seal the CC and put a vacuum/fuel-pressure gauge on the dipstick, to make sure there is No vacuum in it, only modest pressure. If pressure, which should be normal, I do not exceed 3>4 psi as to do so only invites trouble. If vacuum, the intake is sucking air from the bottom, and I gotta take it off, find out why, and fix it. Then when I get a satisfactory conclusion
3) With the engine idling, the PCV correctly plumbed and properly working, I would first check to see that all vacuum taps are sealed, that the Vacuum advance is on the spark-port and is NOT working at all, and then, one atta time, I would pinch off all the other vacuum devices to be sure none are sucking wind. When satisfied,
4) I would remove the carb, drain it, flip it upside down, make sure the Primaries are on the curb and the that the choke is disengaged. Then I would adjust the Secondary throttle blades to be fully closed but not sticking. Next I would open the Primaries and set them such that the Transfer-slot exposure on the underside is between square to slightly taller than wide. Next I would grab the Base gasket and make sure it actually properly fits the bottom of the carb and the intake, leaving no paths to atmosphere that should not be there. Next, I would flip the Carb rightside up and adjust the mixture screws to 3/4 turn out, and reinstall it. From this point I would absolutely not adjust the curb-idle screw.
At this time, I gotta make a few assumptions, namely
a) that the Wet fuel level is correct and remains stable, if I have to, I'll check it out later.
b) that the gas is fresh and uncontaminated
c) that the bowl vent is open
d) that the fuel tank is vented.
e) that the cooling system runs at a stable and acceptable temperature
f) that the air motion of the fan is not upsetting the bowl-vent,
g) that the PV is not ruptured
h) that all the airbleeds are clear
j) if you are using an adapter under the carb, you gotta check it, and it's gasket also for compatibility.
k) that the plugs are all clean and the wires are all properly and satisfactorily routed, and the cap is neithe cracked nor burned up nor filled with moisture.
l) that the cam-timing is at least close to correct, and that the valve lash, if any, is correct and not too tight, and if Hydros, then that the lifters have properly bled down.
and so, I come to
5) the tune up.
At this point it should idle perfectly down to 650 in N/P with as little as 5*advance.
At this point, I will not adjust the Idle speed with the speed screw cuz that would defeat the purpose of having taken the carb off to set the T-Slot synchronization! Instead, if the idle speed needs adjusting, I will use timing. The more you give it, the more idle- power the engine will make, and the higher the idle-speed will go.
As for Idle rpm, I only want enough to idle at as low an rpm as will not bang the trans when I stick it in gear. If I can do this with 750 in N/P and 650 in gear, that's what I'm looking for. I don't care what the Idle-timing ends up being. and so we come to the shake
6) to cure an Idle-AFR shake, you only have to adjust the Idle-AFR, lol. At this stage, I leave the vacuum gauge in the toolbox, cuz it can't tell me chit on a 268 cammed 318-stroker, that my eyes, ears, and nose, don't already know.
>If the exhaust is burn-your-nose stinky, simultaneously with the idle-shake and the mixture screws set to in the range of 1/2 to 1.0 turn out, then I would bet money that the engine wants some Idle-Air bypass. Proving it is easy; I just pull the hose off the PCV and stick my thumb over the hole, adjusting the airflow, until the engine smooths right out and the stink in the tailpipe goes away. real simple. More complicated is to actually make a permanent solution to this problem. The Way I do it, is to calculate the size of the hole that I'm getting off the PCV, and drilling the Primary valves to an appropriate size.
If I drill too big, the Idle speed will go up, and if too high, then the only way to bring it back down is to retard the timing. If the timing goes too low, the engine will begin to be sluggish in running up to the stall-rpm. This is exacerbated with low cylinder pressure. Ok so, I try to keep the Timing in the window of 12>18 degrees with an automatic, and 10>14 with a hi-pressure stick-car. O so now, she's running pretty good, assuming all my assumptions were good ones. Well not quite
7) she has to pass one more test. the tip-in test.
with the trans in gear, and the idle speed around 650, the engine must not hesitate, when you very slowly tip the throttle in. So then your first adjustment is to make sure the Accelerator pump begins delivering fuel, the instant the throttle moves; adjust as necessary. Next, if any hesitation remains, and the mixture screws are properly adjusted, there are only three ways to cover that tip-in hesitation, namely, with additional transfer fuel, or with increased Wet fuel level, or with the IABs. So the first check is the fuel level. the Second is to crank in the speed screw giving more fuel from the transfers....... however this has the side effect of also bringing more air to the party. Sometimes this makes the tip-in hesitation worse. Which means I'm gonna have to close up my bypass air, dammit. Moral of the story is easy on the bypass air..... lol
Ok so, whadImiss?
>Oh yeah, if you are running a drop-base air cleaner housing, you gotta make sure your bowl vent does not get too close to the lid. They say, AND I cannot confirm, that 3/4 inch is the minimum. and
after you get the Idle all tikkity-boo, then you still gotta work our your Power-timing, and Part-Throttle timing, and your Cruise- timing.

That's what I would do, if the balancer turns out to be fine.........
 
^ ^ ^

20230807_213907.jpg

Scope readings like this as one cylinder.

Times 8, all 8 cylinder ignition patterns should look the same for a good running engine. If there is one oddball pattern, then that is the one with a problem.

My cousin had a scope at his Union 76 Service Station in 1976.

Used to watch the live scope patterns on the screen as the shop mechanics were doing their tune ups. "Scope Check" was frequently written on the work orders.

They could also kill one cylinder at a time to hunt for a weak cylinder.

Can also do this test by pulling One wire at a time out of the distributor cap, to hunt for a misfire cylinder.

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George Jets said:
^ ^ ^

View attachment 1716124764
Scope readings like this as one cylinder.

Times 8, all 8 cylinder ignition patterns should look the same for a good running engine. If there is one oddball pattern, then that is the one with a problem.

My cousin had a scope at his Union 76 Service Station in 1976.

Used to watch the live scope patterns on the screen as the shop mechanics were doing their tune ups. "Scope Check" was frequently written on the work orders.

They could also kill one cylinder at a time to hunt for a weak cylinder.

Can also do this test by pulling One wire at a time out of the distributor cap, to hunt for a misfire cylinder.

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Click to expand...
That somewhat resembles my current feeling for this car.
 
I wish you had another carburetor to try. I think you're gonna find it has an internal vacuum leak.
 
Lifter/lobe failed or failing.

Engine idling, short out the spark plugs one at a time. If you have a digital tach, you will be able to see accurately which cyl lose more rpm. The cyl that drop less rpm are the faulty ones.
 
Whose 4” rotating assembly did you use? And did you have it balanced or was it sold as a balanced assembly?
 
TT5.9mag said:
If you can cover the primary bores and/or close the choke with no/little effect then it’s running on air from somewhere. Either the secondaries are open or it has a vacuum leak. Period. Pull carb off, turn it upside down and close the secondaries down tight, but not sticking. Then re tune the primaries.
Click to expand...
This! Of course, you could have a balance problem, too.
 
TT5.9mag said:
You weren’t given a build sheet or any docs with the engine?
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There might have been a sheet from the machine shop that had some charges for machine work. I would have to pull the folder out and check through it all again.

The VERY first thing I noticed about this car when I got it was the idle was set at like 1100-1200 rpm.
 
67Dart440GT said:
904 auto
Click to expand...

Hopefully your Flex Plate looks like this stock 318 one. Or the solid disc aftermarket one for the 904.

Screenshot_20230808-122324_Firefox.jpg


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Do not want a flex plate disc with the notch cut out of it for balancing the likes of a 360 external balance, or that will cause your vibration.

Also do not want the balance weights on the torque converter either.

Screenshot_20230808-122149_Firefox.jpg


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George Jets said:
Hopefully your Flex Plate looks like this stock 318 one. Or the solid disc aftermarket one for the 904.

View attachment 1716124970

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Do not want a flex plate disc with the notch cut out of it for balancing the likes of a 360 external balance, or that will cause your vibration.

Also do not want the balance weights on the torque converter either.

View attachment 1716124971

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Click to expand...
It is the correct stock one.
 
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