Mild 318 misses at 3000rpm

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DusterDaddy

DusterDaddy

sledgehammer mechanic
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Mild 74 cast date 318 build
30 over, kieth black hyperT pistons, Mopar P4452757 cam, stock heads ported/blended with 1.88/1.6 valve job, performer intake, Holley Street Avenger 600, Pertronix flamethrower HEI module and coil, stock remanufactured electronic ignition distributor. Everything is new. Had a an intake manifold leak I fixed. Initial timing is 20* total is 32* timing is steady when the miss happens.
Could be the pickup in the dizzy???
And ideas?
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That would be my guess.
 
Small blocks love initial timing but you may be advancing to quickly for your setup
Thats alot of initial for that cam. Im only running 18 initial with my .508/292 degree cam.
At what rpm is your 32* coming in at?
 
Oldschoolcuda said:
Small blocks love initial timing but you may be advancing to quickly for your setup
Thats alot of initial for that cam. Im only running 18 initial with my .508/292 degree cam.
At what rpm is your 32* coming in at?
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I'm here alone today, tach is in dash. If I had to guess I'd say maybe 2000.
I ran it with the vacuum advance disconnected and it does not like that 20* at higher rpm.
 
DusterDaddy said:
I'm here alone today, tach is in dash. If I had to guess I'd say maybe 2000.
I ran it with the vacuum advance disconnected and it does not like that 20* at higher rpm.
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2000 rpm is to fast for your specs. You probably want your total coming all the way in at 2500 plus.
Do you know what mechanical advance is in your distributor?
If stock unit without mods you could have 26 to 30 degrees mechanical advance you are adding 20 initial too. Not good.
 
Oldschoolcuda said:
2000 rpm is to fast for your specs. You probably want your total coming all the way in at 2500 plus.
Do you know what mechanical advance is in your distributor?
If stock unit without mods you could have 26 to 30 degrees mechanical advance you are adding 20 initial too. Not good.
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I don't know. " Jim I'm a carpenter, not a mechanic!!"
Dizzy is a stock reman off the shelf at Napa for a 74 318
Going to get another i case the pickup is bad. I'll ask if they can tell me what the mechanical advance on it is.
So where would you set initial?
 
You are probably getting a reman smog unit that probably has 28 to 30 mechanical built in at least.
Try setting your initial at 5 and work from there to see if that corrects your missfire prob. You really dont want more than 34 degrees total with todays pee pee fuel.
It is worth your while even with your light mods to get a decent adjustable distributor.
Contact Trailbeast. He can hook you up with a great setup on the cheap
 
The distributors have an air gap adjustment that many do not know of. Since the reluctor and pickup are magnetic, you need to use a BRASS feeler gauge and set the gap to .008". I've had the gap widen to .020 and while the car idled fine, it would pop and stumble at anything over half throttle.
 
Not enough timing "20 initial/32 total" to detonate in neutral with no load, those carbs are too lean ootb fyi.

Are you sure of your timing settings?

If so, and you verified what kerndog said with airgap...then it's lean.
 
I am as certain of timing as I can be. Advance timing light at 20* initial. I will connect dizzy vacuum pot to manifold vacuum so it advances fully and check reading.
I have a new Mopar dizzy on its way to local store for tomorrow so we will see. I'd rather have new than remanufactured anyway

What is ootb?
 
Sorry, rotor phasing is the position of the trigger in the distributor in relation to the terminals in the cap. Due to the small block dist being so small in diameter there is not much room for error before the spark might jump to the next terminal or be very weak. Search MSD rotor phase for a very good video. Then take an old cap and drill hole near number one tower. Hook up timing light and see how far off the rotor is when it triggers.Vacuum advance alters the phasing.
 
Mine was just like the before on the video. A long and eradic spark at about 3000 rpm. Because I don't run a vacuum advance I cut the link and rotated the plate until the phasing was correct. Then drill through both plates and screw them together.
 
I wonder if the high energy spark from the HEI is making any issues with the distributor more pronounced. It is like lighting compared to the spark from the stock ignition...
 
I see everything is fresh. I was hoping that you just switched distributors and that's when the problem started. Without a scope to see the ignition pattern, it's just a "check this and replace" that kind of repair. You could throw in a known good distributor with a ballast resistor and see if it's definitely ignition. I chased a bad idle on my newly rebuilt 273 for 2 years before I found the Autolite plugs were too cold. You'll figure it out. Just a matter of time.
 
toolmanmike said:
I see everything is fresh. I was hoping that you just switched distributors and that's when the problem started. Without a scope to see the ignition pattern, it's just a "check this and replace" that kind of repair. You could throw in a known good distributor with a ballast resistor and see if it's definitely ignition. I chased a bad idle on my newly rebuilt 273 for 2 years before I found the Autolite plugs were too cold. You'll figure it out. Just a matter of time.
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As noted. I found a new, not remanufactured dizzy that I can have in the morning. That's the first thing I'll swap in and I'll roll the initial timing to 5* and see what it does.
 
Ootb = out of the box. Stock setting, the phasing is hit or miss on even new distributors.
 
Yes, it can increase the ionization inside the cap that can cause spark scatter
 
furrystump said:
Ootb = out of the box. Stock setting, the phasing is hit or miss on even new distributors.
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Got ya. Looks like a set of brass feeler gauges in on my future.

I was more adept at this when this car looked like this
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It took me 6 years but I got it to look like this on my own other than paint. I get a sick to my stomach when someone says set the gap to .008 and use brass feeler gauges. lol. Bashing and grinding are more my thing!

IMG_7660.JPG
 
furrystump said:
Yes, it can increase the ionization inside the cap that can cause spark scatter
Click to expand...
There was a batch of mopar distributors late 90's-2001 roughly, that had phasing problems. The top shaft was machined so that it clocked the rotor wrong. Had it happen to me....but it ain't effecting **** till 4000+ rpm and you would not hear or see it like he is at 3000 rpm. The other thing is its specifically the number 5 cylinder that was affected by the phasing issue and would scuff the skirt of only that cylinder alone.

Been around that corner.
 
to check rotor phasing: drill a 1/2" hole in the dist cap top flat area 2/3 of the way from the center cap terminal to the #1 cap terminal & shine your timing light down in the hole to "freeze" the rotor position like a strobe light does on a dance floor. You want it close to dead on with the #1 terminal & try it with the can disconnected/plugged & idling and with the can connected on a fast idle so you are up on manifold. Only vac adv, not mechanical adv or idle speed changes RP. Ideally you want it a bit on the CW (trailing) edge of the cap terminal as RP will shift it back CCW on a SB. The hole will help let out ionized air molecules in the cap (as said helps prevent crossfire) or for aesthetics if desired drill a hole in a junk or spare cap instead. to fix it; redrill another hole for the roll pin in the reluctor. drill a bit inward from the center ID hole then break it out to the ID with a minirat tail file, duplicating the OE roll pin holes. Do carefull measureing & if off there is plenty or room to drill another one. also a good idea to drill out the rotor blade rivet & add a longer piece so there is .015" from rotor tip to cap terminal as this radial clearance distance adds into the RP (circumferential arc) distance & if the required voltage needed for the combined gap is greater than what the available voltage can jump then it will misfire
 
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