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7/12/2021 8:09 PM  #1


What is the correct sparkplug?

I'm still having trouble with my ignition system. It is a Duraspark with a new Spectrum brand distributor, new Ford Racing wires, new stock Standard T coil, new cap and rotor, and new Autolite 3923 plugs. It cuts out at 3000 RPM and up. I've gapped the plugs to .055 with no change. I've checked the timing to be at 6° BTDC and set the inside of the distributor so it won't go past 35° BTDC at 3500 RPM. With the vacuum hooked up it goes past 60° BTDC. When I did the internal adjustment to the distributor the gap between the rotor and the stator (?) was over .030. The Ford manual says it's supposed to be at .007.  When I rechecked the gap on the plugs I noticed that the #1 and #2 plugs were completely white and the electrodes totally clean but discolored from the heat. The rest of the plugs had a little carbon on them but still discolored from the heat. What is the plug that can take a .055 gap and is the next step colder?   


Sometimes ya just gotta fly low.     70 convertible 76B model, L code out of the box. 416W stroker now.
 

7/13/2021 5:48 AM  #2


Re: What is the correct sparkplug?

0.055" is a REALLY big gap.  This is what we used to run in 5.0s that had all the best ignition stuff.  On anything else I'd run more like 0.040".

I don't think this problem is spark plug related.  Typically when an engine won't pull past 3,000-3,500 its spark scatter caused by the module not having enough dwell time for the coil built in.  Though, the gap for the stator could also be an issue if its out of spec.  0.007" is too tight though.  The spec I've seen is 0.015-0.025".  Granted 0.030" is a bit on the wide side, but typically there isn't a way to adjust it other than elongating the hole in the pickup to allow you to move it in or out, or very carefully bending the plate. 

 

7/13/2021 8:30 AM  #3


Re: What is the correct sparkplug?

Try closing gap to .045-.050

The 78 Granada and LTD 302 & 351 engines had .050 gap with a Duraspark II ignition system.

Is the center tab on rotor making good  contact?
Any build up on cap terminals inside?

Might want to check for loose or poor connections in wiring too…bad crimp connection?


Dan - Never a Yooper! Eh?
 

7/13/2021 4:19 PM  #4


Re: What is the correct sparkplug?

How old is the battery?!
6sally6


Get busy Liv'in or get busy Die'n....Host of the 2020 Bash at the Beach/The only Bash that got cancelled  )8
 

7/13/2021 7:47 PM  #5


Re: What is the correct sparkplug?

Well so much for reading articles on the Internet. Quite honestly the engine has been running so rotten since building it I don't know which way to turn first between the carb and the ignition system. Back in the old days on old cars you could take it to the shop and put it on the oscilloscope and adjust it. There isn't a shop that has one any more. Shop don't have on car tire balance machines as well.

6sa6,  The battery is a "good" one. Has 12v according to the gage and goes up to 14 on start up. I converted to the gen 3 alternator awhile back. The windshield wipers run faster now. So what does the battery have to do with the ignition system if the alternator is putting out the volts and amps? The engine fires on the first crank most of the time if it was run the day before. (Except at the bash)


Sometimes ya just gotta fly low.     70 convertible 76B model, L code out of the box. 416W stroker now.
     Thread Starter
 

7/13/2021 9:57 PM  #6


Re: What is the correct sparkplug?

Had the same thing happen a few years back (breaking up above 3000RPM almost like water in the fuel.) I changed plugs I cleaned plugs I checked timing I checked wires poured cr-p in the fuel tank on & on.
A few weeks (or days, can't remember) Battery wouldn't hold a charge...finally died.
Replaced battery and problem has never returned.
S'why I axed........
Hope you figger it out
6sal6


Get busy Liv'in or get busy Die'n....Host of the 2020 Bash at the Beach/The only Bash that got cancelled  )8
 

7/14/2021 7:52 AM  #7


Re: What is the correct sparkplug?

Check your vacuum advance can and make sure it holds vacuum. A leaky one can cause all sorts of strange running.
6 degrees of initial timing may not be enough. I find that 10-12 works best with the fuels we have now. 10-12 initial and then set the vacuum advance to only 6 degrees additional.

Last edited by RV6 (7/14/2021 7:54 AM)


Gary Zilik - Pine Junction, Colorado - 67 Coupe, 289-4V, T5
 

7/15/2021 6:01 AM  #8


Re: What is the correct sparkplug?

Figuring out initial advance depends on how much mechanical advance is in the distributor.  You have to determine total timing first.  On a built engine like that 416 I would say total timing is going to be in the 32 degree range.  So if there's say 26 degree in the distributor for mechanical you set initial advance at 6 degrees.  If the mechanical advance in the distributor is adjustable you may be able to experiment with more initial and less mechanical, etc.  The key is not to exceed the maximum timing figure, which is best determined under controlled circumstances (dragstrip or dyno), though if you look at where most high performacne engines with modern heads are happy its usually right about 32 degrees total.  At the very least I would start there. 

 

7/15/2021 9:45 AM  #9


Re: What is the correct sparkplug?

Although my setup is different, I have an MSD 6A box and mechanical distributor.  I also have Edelbrock heads, Edelbrock recommeds Champion Plugs in the follwing models RC9YC to RC14YC.  I'm using RC12YC and do not have any issues with them.  I have about 12 degrees initial advance and about 36 degrees total.


65 Fastback, 351W, 5-speed, 4 wheel discs, 9" rear,  R&C Front End.
 

7/15/2021 11:52 AM  #10


Re: What is the correct sparkplug?

HudginJ3 wrote:

..... the #1 and #2 plugs were completely white and the electrodes totally clean but discolored from the heat. The rest of the plugs had a little carbon on them but still discolored from the heat.   

I might be out in the broccoli patch, but is it starving for fuel? 

Has the car done this since you got the motor back together, was it doing it with the last motor, did it start with an ignition change? 


John  -- 67 Mustang Coupe 390 5 speed
 

7/15/2021 9:35 PM  #11


Re: What is the correct sparkplug?

Bolted to Floor wrote:

HudginJ3 wrote:

..... the #1 and #2 plugs were completely white and the electrodes totally clean but discolored from the heat. The rest of the plugs had a little carbon on them but still discolored from the heat.   

I might be out in the broccoli patch, but is it starving for fuel? 

Has the car done this since you got the motor back together, was it doing it with the last motor, did it start with an ignition change? 

That's a different story or so I thought. But it's long. Ever since the original build it has pinged. The hotter it got the worse it pinged. It got so bad that I would retard the spark as I drove along. The Florida bash trip was the worst. I didn't understand total timing till I read something about it on here. Before that I installed a Pertronix then a Pertronix II and then the current Duraspark trying to fix it. I tried every sparkplug I could think of thinking the heat range would fix it. Then I learned I was going the wrong way with hotter plugs instead of colder plugs. So I have a whole boat load of plugs I can't do anything with.  Then I read that the Autolite's were better than the NKG's I was using so I switched to them. That's why my question in the title. I'm thinking it's the wrong question. Then thinking I have an understanding on total timing I put a bushing on the mechanical advance stop and bent it to 35° BTDC. It's hard to get it just right. Because the dist is a Spectro brand I can't use an Autolite advance rotor (?). (I did that because it was going past 65° BTDC.) and set the initial timing to 6° BTDC.  
So now to your point about the fuel. If I floor it WOT, before the RPM's got up to 5K the carb ran out of gas. I put an electric fuel pump on it and that helped. I am now able to shift thru all 5 gears then it runs out of gas. I put the bigger needle and seat in the carb but that didn't help, so I just don't go to fast very long. If I let off the gas the carb fills back up and runs fine. I can only guess that the plugs are too hot but I don't have 500 miles on the last build yet so Im thinking it's not broke in completely.               I don't remember but I think I changed the gap between the rotor and the stator at the same time that I retarded the mechanical advance.

 


Sometimes ya just gotta fly low.     70 convertible 76B model, L code out of the box. 416W stroker now.
     Thread Starter
 

7/15/2021 11:06 PM  #12


Re: What is the correct sparkplug?

I surprised my ole Boss a while back he was thinking the 1976 Bronco with the factory 302 would've had the same gap as the 1964-73 mustangs he's use to, he was so shocked when I told Him what I set the plugs at They plugs were set at  0.044 gap.  He thought there's no way it'll run to his surprise it stared right up and sounded very healthy.

 

7/16/2021 4:31 AM  #13


Re: What is the correct sparkplug?

Ah-ha!

I did same thing many years ago with timing.
When timing is retarded, it makes the engine run hotter.
I was fighting  this in 90+ degree weather in Cali.

I ended up with around 12-14 initial advance and adjusted mechanical as needed..
Then connected vacuum advance for part throttle/cruise.
On my Edelbrock 1406 carb, it ran best on full vacuum port with Performer 289 cam.
I tried ported several times and just didn’t run right to me.

When you say advance got to 65 degrees, was that at cruise/part throttle?

Last edited by Nos681 (7/16/2021 4:34 AM)


Dan - Never a Yooper! Eh?
 

7/16/2021 9:41 AM  #14


Re: What is the correct sparkplug?

HudginJ3 - regarding running out of gas ... with what you've posted I'd first check the fuel line externally for it being crushed somewhere, then check the filter in the gas tank pickup tube, then the internal fuel line for a restriction.  If you find the gas tank pickup tube filter is clogged, check the internal gas tank for rusting that may be source of it being clogged. 


65 Fastback, 351W, 5-speed, 4 wheel discs, 9" rear,  R&C Front End.
 

7/16/2021 5:07 PM  #15


Re: What is the correct sparkplug?

BobE wrote:

HudginJ3 - regarding running out of gas ... with what you've posted I'd first check the fuel line externally for it being crushed somewhere, then check the filter in the gas tank pickup tube, then the internal fuel line for a restriction.  If you find the gas tank pickup tube filter is clogged, check the internal gas tank for rusting that may be source of it being clogged. 

Strange you would mention that. Back in around 79 I was driving in the rain in the mountains pulling a camper trailer. I came to a sharp corner and drove almost over a cliff. The only damage was to the fuel line. I bought a new one but never replaced it till recently thinking it was causing the fuel issue. The reason I never replaced it was I had odered one for a Boss 429. Turns out it is the same one used for all Mustangs for the 250 - 6 cylinder and up. I never thought that the fuel sender could be plugged up. It's only 51 years old. Right now the tank is full of course.
(I wonder if running distilled vinegar will clean out the gas tank???  ( it's a joke guys ))
 
Nos681
The 65° advance was at 3500 RPM and more. I have the dist out now and can only guess how far to adjust it. Although I think TKO's advice is where the problem is......We'll see.

 


Sometimes ya just gotta fly low.     70 convertible 76B model, L code out of the box. 416W stroker now.
     Thread Starter
 

7/17/2021 10:38 AM  #16


Re: What is the correct sparkplug?

How do you know it’s running out of fuel? Floats are set to allow for plenty of fuel?

For my Holley, I set them per the old standard of being at the bottom of the site hole with a little dribble out when you rock the car. I had to lower them a little more when I noticed fuel boiling out into the throttle bores when I killed it after driving

How hard would it be to plumb your electric pump to a can of gas in the truck for a test drive? That would eliminate anything with the sending unit and sock in the tank.

My distributor has the adjuster inside the vac canister to limit total travel. Is that an option for you?


John  -- 67 Mustang Coupe 390 5 speed
 

7/17/2021 2:34 PM  #17


Re: What is the correct sparkplug?

Another thought is are you sure that the TDC mark on the balancer is really TDC #1?  Ford used 3-4 different pointer and balancer combinations and trying to read the wrong balancer/pointer combo could have the timing off by 40-60 degrees (or more) and easily cause detonation even when everything else seems right. 

 

7/17/2021 5:02 PM  #18


Re: What is the correct sparkplug?

https://www.summitracing.com/parts/sum-900189?rrec=true
Best way to ASSURE you have found TDC is one of these....(I made mine butt......for 10 bux  that's hard to bet!)
Use one of these ^^^^ mark your balancer/dampner ......buy a cheap timing tape for your diameter of balance/dampner and ......UR golden (like Ms. Hawn!)
6sal6


Get busy Liv'in or get busy Die'n....Host of the 2020 Bash at the Beach/The only Bash that got cancelled  )8
 

7/17/2021 6:43 PM  #19


Re: What is the correct sparkplug?

Bolted to Floor wrote:

How do you know it’s running out of fuel? Floats are set to allow for plenty of fuel?

For my Holley, I set them per the old standard of being at the bottom of the site hole with a little dribble out when you rock the car. I had to lower them a little more when I noticed fuel boiling out into the throttle bores when I killed it after driving

How hard would it be to plumb your electric pump to a can of gas in the truck for a test drive? That would eliminate anything with the sending unit and sock in the tank.

My distributor has the adjuster inside the vac canister to limit total travel. Is that an option for you?

 
I've run out of gas many times, it has the same symtoms. But let off the gas for a second and then good to go. It only happens when it is in second or third at high RPM.

My vac advance has the adjuster in it. I checked TDC when the engine was apart and had already put a tape on it. That's how I am reading 65º. And I have that fancy piston stop tool.


Sometimes ya just gotta fly low.     70 convertible 76B model, L code out of the box. 416W stroker now.
     Thread Starter
 

7/17/2021 8:38 PM  #20


Re: What is the correct sparkplug?

How bout the vent for the gas tank?!      Ck it?!
6s6


Get busy Liv'in or get busy Die'n....Host of the 2020 Bash at the Beach/The only Bash that got cancelled  )8
 

7/17/2021 9:29 PM  #21


Re: What is the correct sparkplug?

It,s part of the gas cap. It wouldn,t be much to leave it off for a little bit.


Sometimes ya just gotta fly low.     70 convertible 76B model, L code out of the box. 416W stroker now.
     Thread Starter
 

7/18/2021 6:55 AM  #22


Re: What is the correct sparkplug?

What compression ratio are you running?  Iron or aluminum heads?

 

7/18/2021 9:10 AM  #23


Re: What is the correct sparkplug?

TKOPerformance wrote:

What compression ratio are you running?  Iron or aluminum heads?

This is something I was wondering about as well. The excessive pinging brought it to mind.

Are you running 93 octane gas? I had a 93 F150 that wanted at least a mid grade fuel to not ping with the timing set to factory spec. The truck had almost 200k on it when I bought it.


John  -- 67 Mustang Coupe 390 5 speed
 

7/18/2021 2:14 PM  #24


Re: What is the correct sparkplug?

CR as near as I can figure it is 9.7 with Eldebrock Performer heads.
I have only run 93 auto gas and occasionally 100LL octane ave gas when I could get it. It pinged on that too. But it hasn't pinged since I set the high RPM timing to 35°. Defined as 3500 RPM and limited the advance to 35°.  


Sometimes ya just gotta fly low.     70 convertible 76B model, L code out of the box. 416W stroker now.
     Thread Starter
 

7/19/2021 6:05 AM  #25


Re: What is the correct sparkplug?

Okay, so the pinging seems a non issue.  I would still say 35 degrees total for an engine with modern heads is a lot.  On an engine like that I'd start at 32 and see if my track times picked up or went down by adding 2 degrees from there.

So this leaves either running out of fuel issue or a spark scatter issue.  On the fuel side I would make sure it has a 3/8" fuel line and if it doesn't swap that over.  It has to be 3/8 from the sender to the carb.  Most of these cars had 5/16 fuel lines from the factory and its just not enough volume for a serious engine.  Carbs need a big fuel line because the pressure is so low.  EFI cars can make 550+HP on a 5/16 line. 

 

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