Misfire mystery

[Rob Doe]

There are ways to use jumper wires to temporarily bypass virtually all of the normal ignition circuit wires. The vendors sell a jumper for bypassing the large cable from the coil + to and through the ignition switch and down to the distributor. I have two of them in my 'on board' tool bag. One I made and another purchased.

If you are running the modern style upper plate, mine is from Nu Rex, a jumper is easy to set up with a plain 16 gauge wire and a small tie wrap. I believe Nu Rex sells a set that allows for a quick plug and play example for roadside repairs.

[Fairlane514]

You are correct, what I have seen on vendors sites is a roadside cable. It has the screw in end and then on the other end an alligator clip to clip to the positive side of the coil (positive ground system).

I could probably make one from the remainder of my cable and see if this really is the fix.

https://www.snydersantiqueauto.com/p...6239&cat=41721

[Rob Doe]

The Nu Rex one is different and does not require removing the distributor. Your light weight cable probably unscrewed from the distributor without removing the distributor from the engine. If the car had the stock switch and heavy cable with the hold down clamp on stud #8, the distributor has to unscrew from the cable rather than the cable from distributor. It's best to drain the coolant down below the head to prevent a head gasket failure.

I had to search the Nu Rex site to find theirs.

[Fairlane514]

I have the NuRex ignition switch that looks like the pop out. I also have the small cable that unscrews from the distributor without removing it.

[SHEC]

So tell us please your remedy for the situation. It’s been an interesting thread and I hope you can now offer a solid result re. parts and adjustments. Thanks for your persistence and patience and from the many Barners offering input . Did you end up with a heavier cable?

[Fairlane514]

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Today's shenanigans ........

While waiting on the new cable, I decided to try and salvage the old one. I cut off the affected area (what I could see) and spliced new 14 gauge wire in place.

No change, same misfire and puff puff in a random sequence.

I dropped the exhaust (new Aries) and started it, no change, just louder...

It could be the remaining original ignition cable is still bad.

I ordered the same small cable, but apparently they are out of stock with no ETA, so they are sending the heaving cable......the wire inside is probably the same gauge as the small cable....

[SHEC]

Originally Posted by Fairlane514

Today's shenanigans ........

While waiting on the new cable, I decided to try and salvage the old one. I cut off the affected area (what I could see) and spliced new 14 gauge wire in place.

No change, same misfire and puff puff in a random sequence.

I dropped the exhaust (new Aries) and started it, no change, just louder...

It could be the remaining original ignition cable is still bad.

I ordered the same small cable, but apparently they are out of stock with no ETA, so they are sending the heaving cable......the wire inside is probably the same gauge as the small cable....

Many thanks and an interesting discussion. The mention of the puff puff sound
( mentioned by others ) also rings a bell at times for me and our Coupe.
Good luck with the new cable and we will see you on the FORD road….

[Fairlane514]

https://www.youtube.com/shorts/RxZxK0TB8SY


This is not my car, but mine sounds similar to this..

You have to turn it up to hear the puffing

[Bill G]

I have a similar problem at idle and runs great otherwise with lots of power. Most of the guys in our circle of Model A's brush it off and say "It's a Model A - what do you expect?" For a long time I still pressed on looking for the magic silver bullet. Still haven't found it. Something within the 95 year-old engine which has been fiddled with and had umpteen sets of valves, valve seats and so forth - is off and I just can't find it. I have come to the conclusion that dealing with what I have is cheaper than going for a whole new engine. It just doesn't run as smooth as my 2022 Honda.

[Fairlane514]

https://www.youtube.com/shorts/XKCX0bjRjEw


This is my car.....

[Lawrie]

One thing I notice ,is every time there is a little click click in the engine ,the vacuum drops.
Maybe in the valve train, sticky valve,?
Lawrie

[Rob Doe]

Our coupe's puffing is much more noticeable. Is your car's puffing at the tail pipe more pronounced in person than on the video?

Is your vacuum gauge dampened?

The idle seems a bit fast. I haven't done it for a couple years, but if I reset the base idle and iteratively work it down to a slow idle with timing fully retarded to ... say 4 degrees ATDC, the puffing is gone. I run at 500+ rpm to keep blinking out of the LED headlights. We drive at night some.

I check my timing with a test light after locking down the distributor cam to see how many notches of spark advance turn the test light on. I'm usually set at the second notch down from the top.

[Big hammer]

Thank you for the video !
For me your idle speed is high, your timing is advanced by either the hand level or base timing .
With a fast idle the carburetor is starting to pull fuel through the GAV, at a slow idle your GAV should not have any effect
At one puff I saw a whisk of black smoke, black smoke = unburnt fuel
I would move the hand lever up, slow the idle down and adjust the idle air. If you insist or need a faster idle , pull the timing lever down and pull the hand throttle down. I believe Ford talk of a rolling slow idle

[Fairlane514]

All new valves and springs

Yes, Idle is a little high, I need to get another video, but it does the same thing at slower idle. The puff is more pronounced in person than on the video.

My timing is controlled by the Nurex automatic timing system, so my spark lever is not really involved unless I want to go way too far advanced. My timing is set with lever all the way retarded.

It had the same misfire with the original spark advance by lever system. I put the automatic advance in when I changed the valves, head and gasket.

Yes, there is some black smoke when it puffs, indicating rich. I have the Renners jet kit in this carburetor. Plugs are sooty when I remove them. When I lean out the carb the worse it runs. My GAV had no effect at this idle speed.

I will try to get another video at a slower idle.....Its just easier to see the dip in the vacuum gauge at this idle, slower idle, the needle seems more erratic.

My gauge is not liquid filled

[Fairlane514]

My thought was with the damaged ignition cable, I had a weak spark and the unburnt fuel was the result.

I still believe its an ignition issue, but sometimes it helps with other opinions, as I get too focused on one thing.

I do wonder about camshaft and components, but it seems like that would more be more rhythmic.

The puff of black smoke........weak spark......too much fuel...

I will try to get a better video later today

[Rob Doe]

You can pinch the hose on the gauge between two fingers and a thumb, as I remember. Like pinching a garden hose and then release the pinch a bit to smooth out the gauge. I've read that a 4 cylinder engine's firing a cylinder every 180* is too far apart for an undampened gauge??? It works on mine.

You can set your base idle with the manifold gauge also. There is also a WWII youtube video that describes how to use the gauge to id many issues.

[bruceincam]

Mine sounds exactly the same. Worried about it for a bit and, like you, couldn't find anything. Finally ran across and article that said it's "the nature of the beast". Stopped worrying and moved on.

[noboD]

Fairlane, I fixed a similar problem on a friend's Buick. It had amiss that moved to every cylinder. I could run it at a slow enough rpm that you could see no spark alternating from one cylinder to another. That ruled out lots of the things. I took the distributor and an ohm meter and kept testing the wire going to the points. One time it would have current next time not. Turns out the wire going through the bakelite insulator in the side had gotten wet at some time in 100 years and had a rust spot RIGHT where the wire had hardened and cracked the insulation. It grounded whenever it wanted to causing the miss. I was lucky to find it. Replaced the wire and insulator and problem was fixed. Not saying this is your problem but the little things matter and can drive you nuts. This car had that miss for 20 years.

[Fairlane514]

Thanks everyone for the responses....

I have tried two different distributors, one has the new style points/condenser, the other has the original style...no change

Could be the nature of the beast, I hate to admit defeat.....

Im going to try cleaning my plugs with a propane torch. I would be inclined to leave it alone, but it if causes my plugs to soot up regularly......hard to ignore.

Could get any video today, but plan on working on it tomorrow ....

[GPierce]

In the early part of the video in post 110 it looks like the #1 spark plug is firing between the base of the porcelain insulator and the steel spark plug base. I.E. the plug is shorted to ground. You can see the spark jumping.