New Miss

[Rand]

Hi there...
I've developed a miss in my 50 Merc that I just cant seem to pin down
It idles fine
Runs fine cold
But once 1/2 way warmed up it miss's
Never has flat out died

This is what I've done so far...
1) Changed condenser
2) Changed coil
3) Changed spark plugs
4) New points
5) Ran engine in dark looking for plug wires sparking
6) Fresh rebuilt Carb by Daytona
I cant figure out why it miss's when its warm and not when its idling or cold??
Seems electrical idk??

Kinda acts like when my loose OD wire grounded out. checked that its ok

Could it be fuel filters? seems electrical tho?
I have a filter back by the tank and the electric pump
and I have a Napa filter in the glass bowl
could it be the cork gasket at the glass bowl
Seems if it was fuel related it would do it all the time..No?

Thanks for your suggestions,
Randy

[JSeery]

Sounds like it could be the coil, are you sure the replacement coil is good?

[Rand]

I tried two different coils
I'm wondering if it could be the wire in the Dizzy shorting out?
Randy

[JSeery]

How do you know the second coil is good?

[40cpe]

It sounds like you are saying it shakes, jumps, and stumbles when this happens instead of a steady, regular miss on one cylinder? You still need to determine if it is ignition, fuel, or mechanical. A squirt of starting fluid in the carb should change it if it is fuel. A timing light with the pick-up moved around on the coil wire and different plug wires should pick up on an ignition problem.

You didn't mention checking the distributor cap and rotor for cracks or breaks.

[tubman]

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I had an O/T MG Magnette with a similar problem. It turned out that the fabric covered wire inside the distributor has rubbed through on the bottom and was intermittently shorting out on the point plate inside the distributor. It looked good from the top, but when I finally took the distributor out and completely disassembled it, it was obvious what the problem was.

[Kahuna]

Might want to also check/replace the distributor cap, if not done already?

[51 MERC-CT]

" Ran engine in dark looking for plug wires sparking"
Doesn't mean the plug wires are good.
Especially if they happen to be carbon core wires.

[big job]

Fresh EAB first start everything genuine new. First run on the stand/ muffler tail pipe
(so I can hear it) runs perfect and super quiet. Next day same symptoms you have
then no start. Coil no good, which has 10 min run time. Another new coil DOA.?
Then we seviced a 1959 Lincoln, job done runs perfect, then started skipping?
Tracked it to #2 pulled plug and no tip & insulator "gone". I say hey Napa, what in
hell is going on; answer welcome to America. I'm just a sayin
sam

[Lawson Cox]

[QUOTE=Rand;1243424]Hi there...
I've developed a miss in my 50 Merc

For a second there I thought you had found a new girl friend.

[Lawson Cox]

Send your coil to Skip Haney for 100% rebuild.

[34PKUP]

Originally Posted by Lawson Cox

Send your coil to Skip Haney for 100% rebuild.

Didn't know that 8BA type coils were rebuild-able or even worth the effort.

[flatheadmurre]

When its warmed up and starts missing i would start by giving it some choke to see how it reacts to richer mixture.
Then pull the ignition wires to check if its a single cylinder or random.
If its random a new known good capacitor would be my next to do.

[rotorwrench]

Also check condition of the distributor bushing. A worn bushing allows the cam to move around more than it should and shoots the dwell all over the place. Also check your polarity connections between the coil and the distributor.

[D. Jones]

I bought a new tubular style coil for my 45 pickup as I didn't have a good original. The new coil lasted less than 10,000 miles and died while I was on the local parkway. I put an old original Ford scripted coil on it and it runs fine. I just sent two originals to Skip to have them rebuilt.

Still having problems with condensers, a new one may run 10 miles or 500 miles but never 1000 miles. If I had any hair I'd be pulling it out.

[Rand]

Update...
Today with no improvement I..
1) Replaced the Dizzy Cap and Rotor button, Visually looked at wire in the dizzy and gave it a wiggle. I replaced that wire some time ago.
2) I also did a vacuum test and got 18 to 20 inch reading
3) Hard to determine miss at idle, seems to run fine at idle, miss's while driving in neighborhood, worse turning around in cul de sac. Never has flat out died.
4) Merc has auto choke so I cant pull the choke to give it more fuel. I did hit the mechanical fuel pump switch with no improvement. Also wiggled ignition switch

To do:
Pull Dizzy to inspect wire
Check coil and condenser with a volt meter (how do I do that?)
Change 2 fuel filters
Squirts some starting fluid in carb for more fuel (hard to do while driving tho)
Check plug wires with timing light, how else can I check those?
Replace ignition switch?
Could it be carb related? Fresh rebuilt from Daytona

Any other ideas?
Never has completely died or not started
It feels like electrical shorting out?? but where
and not at Idle??

Thanks for any ideas,
Randy

[rotorwrench]

If your tank has any water in it, some will find a way into the venturis. Fuel delivery problems aren't usually intermittent in nature unless you have a water problem.

[51 MERC-CT]

Originally Posted by Rand

Update...
Today with no improvement I..
1) Replaced the Dizzy Cap and Rotor button, Visually looked at wire in the dizzy and gave it a wiggle. I replaced that wire some time ago.
2) I also did a vacuum test and got 18 to 20 inch reading
3) Hard to determine miss at idle, seems to run fine at idle, miss's while driving in neighborhood, worse turning around in cul de sac. Never has flat out died.
4) Merc has auto choke so I cant pull the choke to give it more fuel. I did hit the mechanical fuel pump switch with no improvement. Also wiggled ignition switch

To do:
Pull Dizzy to inspect wire
Check coil and condenser with a volt meter (how do I do that?)
Change 2 fuel filters
Squirts some starting fluid in carb for more fuel (hard to do while driving tho)
Check plug wires with timing light, how else can I check those?
Replace ignition switch?
Could it be carb related? Fresh rebuilt from Daytona

Any other ideas?
Never has completely died or not started
It feels like electrical shorting out?? but where
and not at Idle??

Thanks for any ideas,
Randy

What type of spark plug wires do you have? (solid core, carbon core or spiro-wound)
If you have carbon core, dump'em and replace with spiro-wound.

[chap52]

Had the same experience awhile back...Changed condenser and all is well. The condenser wasn't that old.
Remember when a new part use to last forever. As a kid I don't remember ever changing out a condenser in my '46 woodie.

[ponymare]

If it just misses on one cyl when warmed up, have you given it a thought that a valve may be too tight?