Gurus help, please- Intermittent engine miss

P

P.S.

Well-known member
The Tudor was running like a swiss watch, just perfect. In fact, I became a little smug about how well it was running, even telling the wife the car is officially "cleared" for long trips now. A couple days ago, I installed a new fuel filter and re-adjusted the fairly new points from 0.17 to 0.21 as the tip of the point block finally wore a little. Also installed a new air maze air cleaner setup. Test drive, car ran great. The air maze actually made it a little quieter. Was very pleased.

Today, jumped in the Tudor to pick up some things from the store (about 8 mile round trip, all 2 lane country roads @ 35-45 MPH). On the way to town, the engine started to miss a beat every 10 seconds or so. Seemed to do it less when on the gas to accelerate. At idle, engine is smooth. Got to the store, got the necessary items and got in, Tudor almost didn't want to start, but eventually did. It did the "miss a beat" thing all the way home. Sometimes not for a minute or so, then would do it every 5 seconds now and then.

After getting home and letting the car cool off a bit, popped the dist cap and cleaned the points. Also pulled the plugs and cleaned them. Checked the timing, etc. All good. Reassembled everything. Went for a drive and the car started doing it again, but not quite as bad as it did on the way home from the store. Turned around and went back home. Thinking maybe the new air maze setup was causing a problem, took it off and went out again. Same thing. Possibly worse after the motor is good and warm than when it is cold. Came back home and turned on computer to ask you gurus what you think might be going on here?

The points and condenser have maybe 200 miles on them. Engine ran absolutely perfect before this morning. Nothing was changed from the last time it was driven 2 days ago running perfect, and now. Ideas, please?
 
Does the miss change if you move the spark lever a little up or down?
Does pulling the choke a little help or hinder?
Was the weather dry, damp, or wet?
 
Miss didn't change with timing adjustment. Richened carb about half turn, no difference. Didn't try the choke because when it wasn't missing, it was running real strong. It just feels like one cylinder not firing at random with all 4 firing 99% of the time. Maybe best described as a random and far-between "stumble".

Using the modern points with wireless plate. Plugs had a little carbon around them, but looked pretty good. They are cleaned now, still doing it. Runs great when cold, begins to stumble randomly after warmed up.

Weather is dry and sunny. Temps in the upper 60's. Humidity 52%.

Could widening the point gap have led to this?
 
Set the points to .020" and have some lube on the rubbing block. Get rid of that wireless plate and you'll get rid of a common source of trouble. I only use original top plates and bottom plates with a very fine stranded wire.

I'd ditch the air cleaner also. You shouldn't have carbon buildup on the plugs. Maybe you need hotter plugs or a leaner mixture.

I assume it isn't an oil burner?

Repro ignition switches can also be a source of trouble. Make sure when it's in the ON position that the contacts make a firm contact. My repro switch would cut out as soon as I touched it and sometimes just from the weight of the small fob swinging back and forth. I made the contacts better and haven't had a problem since then. Also make sure the switch terminals aren't touching the gas tank.

It takes a little effort to make sure the ammeter terminals are clean and tight, as well as the terminal box terminals, so these two spots are often overlooked.
 
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Thanks, Tom.

It had carbon on the plugs even before adding the air filter. It does not burn oil, it usually runs great and real strong. Prior to today- ALWAYS starts right up and runs like a watch.

How do I lean out the high end? It has a Zenith carb. Rebuilt by the shop 2 months ago.

If I disconnect fuel line from the carb and turn the fuel on, it gushes out like a garden hose.
 
Thanks Dave.

Points are only 3 months old. I did check the insulator, points, etc. today when inspecting the distributor. Also took a fine file to the points because I was desperate. The distributor was removed from the motor for a close inspection. Distributor was reinstalled on the car, timing checked, and the same thing happened.

Those solid state ignitions are looking better and better all the time....
 
Tom-

See you edited your post. Here's more info pertinent to your added info:

The wiring is all tight and good. Soldered terminals on #12 or #10 authentic looking wire. Wires on the ammeter are tight. Ignition switch wires are tight, and there is insulation on the back to make sure they don't touch the tank (even though they aren't even close). However, it IS a repro ignition switch, and that is easy to swap out. Will try that. It's not a pop-out type. When it stumbles, the ammeter doesn't wiggle or anything. I would think if it was a wiring problem to the ammeter, it would wiggle when it made/broke contact, no? I made the last test-drive with the lights on, and all looked normal from an electrical perspective. Just a darned intermittent random motor stumble.

I did check the terminal box wiring a few days ago as part of a routine overall check. I found the passenger side nut about 1/4 turn loose and tightened both, then put the cover back on.

Thanks for the input, Ron. I don't have a spare coil around, but perhaps it's time I did.
 
Try turning in the GAV until it's as lean as can be without a stumble. I run with mine closed except for the first 30 seconds or so after a cold start. My plugs stay nice and clean.

Maybe you need a hotter plug.
 
Like you, I always run the GAV completely closed (fully CW) after about 30 seconds or so on a cold startup.. When it's warm outside, I don't open the GAV at all. However, my plugs get some carbon around the outside and on the anode. The center electrode still looks good though.
 
those wireless plates have been known as troublesome since they appeared on the scene, at least for 30 years. It might be something else, but its the first red flag I read in your post. It sounds like bad contact somewhere, but the possibilities for exactly where are many. Let us know when you get it so we can learn something.
 
I recall two cases like yours.

One was a Model A with the safety fuse mounted on the starter. He had a loose wire on one of the terminals that caused his problems. Also I reported before from my own experience that the glass tube fuses have to be checked with a meter as the China made ones may look good but some don't conduct electricity.

The other was a condenser that the mounting tab had broken away from the spot welds holdng it on to the can. It looked OK but if you pushed on the tab with a screwdriver it would run better. Also if your disti has been painted check that it still makes good ground connections going into the head and where the condenser is attached.

Good luck and remember the fix is often the last thing you try. Or the problem was caused by the last thing you tried....:rolleyes:
 
Take your wireless plate out of the distributor turn around and throw it as far as you can. They are worthless pieces of junk. Order a new set up with the wire and that will solve your problem. I never could get a wireless plate to work worth a damn. And it had the same symptoms you describe. And as far as your comment on solid state ignitions, I highly recommend them. In my experiences they work really really well.
 
Just as a shot in the dark, did you try changing the plugs out. I've had an occasion that the plugs looked good but intermittently miss fired. Replacing them cured the problem. Just a thought. Good luck!
 
I had the same problem a few months ago after changing the distributor points block. I suspected that the points were occasionally touching the block. (See photo.) I filed the edge of the points block and it never happened again.
 

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Wow! Thank you all for the excellent input and expertise! Especially Tom's and Logan's, ha ha!

Taking all the expert advice and combining that with my own loss of patience for this- Decided the best way to "chase" this was to not chase it at all and just "shotgun" it and replace the entire ignition system with a stock type setup like Tom advised. Called Bratton's this morning and ordered their complete new distributor with stock points, a new coil, new ignition switch, and all new wiring.

Due to my line of work, I have no patience for temperamental devices or fragile equipment. I refuse to go through this every 4 weeks or so when the car will just act up for no good reason. Decided a complete "do over" is the only way I am ever going to rid this car of these ignition system gremlins.

I thought these cars were supposed to be super reliable??? Mine is always giving me fits!
 
P.S. said:
Wow! Thank you all for the excellent input and expertise! Especially Tom's and Logan's, ha ha!

Taking all the expert advice and combining that with my own loss of patience for this- Decided the best way to "chase" this was to not chase it at all and just "shotgun" it and replace the entire ignition system with a stock type setup like Tom advised. Called Bratton's this morning and ordered their complete new distributor with stock points, a new coil, new ignition switch, and all new wiring.

Due to my line of work, I have no patience for temperamental devices or fragile equipment. I refuse to go through this every 4 weeks or so when the car will just act up for no good reason. Decided a complete "do over" is the only way I am ever going to rid this car of these ignition system gremlins.

I thought these cars were supposed to be super reliable??? Mine is always giving me fits!
Click to expand...

Could it be that nothing is wrong with the car ?... maybe another problem... :rolleyes:.
Good luck.
 
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