Weak Spark on No 1 Plug

[Tom Wesenberg]

Originally Posted by aermotor

Mitch, You forgot the ""defective distributor body and "". To me this doesn't mean the cap was changed - am I missing something?

John

Not sure I understand this statement, but he did state that he tried another distributor top, although it might have been defective also.

I was thinking he could have a tight gap on #1 plug, and this would show a small spark when using the screwdriver short test, but he changed the plugs also.

If he was close by, I could do a scope check to eliminate the ignition.

[aermotor]

[QUOTE=Tom Wesenberg;1438662]Not sure I understand this statement, but he did state that he tried another distributor top, although it might have been defective also.

Oh well, I guess it is just me that I can't find in the OP where the distributor CAP or top - what ever it's called was replaced. I'm a newbie and just try to troubleshoot in my own KISS way.

John

[Greg Jones]

I should have been clearer in my description. I replaced the distributor top as Tom says and not the distributor body. I am intrigued by George's comment on compression (and in a pm from Tbird). In theory compression should be ok but will run the test to be sure.

[Mitch//pa]

Yep a proper diagnosis needs to be performed so u dont go chasing ya tail
Keep us posted

[Tom Wesenberg]

Originally Posted by Greg Jones

I should have been clearer in my description. I replaced the distributor top as Tom says and not the distributor body. I am intrigued by George's comment on compression (and in a pm from Tbird). In theory compression should be ok but will run the test to be sure.

"So I thought, must be a defective distributor body and switched with another. Same results. Switched with another, with same results."

This can be confusing, as Ford called the bakelite part the "BODY". A lot of us think of the body as the cast iron main part of the distributor.

The body can short out internally, and it's usually between #3 and #4. You say you changed it and same results, so that's why a scope check might help now. Otherwise, as Bill said, it could be an intake leak. Just open an unlit propane torch and move it around the intake runners to see if the speed picks up.

It could also be a slow to close valve, and a vacuum gauge can show this.

[Mitch//pa]

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Yes the terminology on a model A can be confusing...

Distributor cap is where the coil wire goes into.
Distributor body is where the plug straps go onto


Correct?

[cpf240]

I'm a bit confused here... the OP said the problem was a weak spark when shorting out the plug when compared to the others. I don't see how compression, or intake, or anything else other than the electrical portion of the ignition system or the operation of the distributor would affect the 'strength' of the spark.

What am I missing?

[JDupuis]

I have a distributor body (wires go on to) that is shorted at #1 and #2. Anything is possible. Jeff

[Bob C]

You got me thinking Mitch so I had to look it up in the Ford parts book.
Body a-12105, Cap A-12115, Distributor Base A-12130.

Bob

[Bob C]

Originally Posted by cpf240

I'm a bit confused here... the OP said the problem was a weak spark when shorting out the plug when compared to the others. I don't see how compression, or intake, or anything else other than the electrical portion of the ignition system or the operation of the distributor would affect the 'strength' of the spark.

What am I missing?

The higher the compression the higher the voltage necessary to fire the plug.

Bob

[Mitch//pa]

Originally Posted by Bob C

You got me thinking Mitch so I had to look it up in the Ford parts book.
Body a-12105, Cap A-12115, Distributor Base A-12130.

Bob

Thanks Bob

[cpf240]

Originally Posted by Bob C

The higher the compression the higher the voltage necessary to fire the plug.

Bob

But he was shorting it out to observe the spark... the spark itself doesn't care about the compression.

[George Miller]

Originally Posted by cpf240

I'm a bit confused here... the OP said the problem was a weak spark when shorting out the plug when compared to the others. I don't see how compression, or intake, or anything else other than the electrical portion of the ignition system or the operation of the distributor would affect the 'strength' of the spark.

What am I missing?

with low compression the spark would jump the plug easy, so there would not be much left for the screw driver test. That is why I said take the plug wire off.

[cpf240]

Originally Posted by George Miller

with low compression the spark would jump the plug easy, so there would not be much left for the screw driver test. That is why I said take the plug wire off.

Ok, I had assumed that the angry pixies would take the easiest path, ie the short, rather than also try to jump the plug gap at the same time.

[George Miller]

Originally Posted by cpf240

Ok, I had assumed that the angry pixies would take the easiest path, ie the short, rather than also try to jump the plug gap at the same time.

Well it would, but we do not know what the easiest path was. How far did the spark have to jump with the screw driver? The plug was probley around .032 if the screw driver was more than that it will jump the plug.

[Mitch//pa]

Quote BobC ''The higher the compression the higher the voltage necessary to fire the plug"""

Bob can u elaborate
Are we talking flameout?

[Greg Jones]

I am going to try George's recommendation after work tonite if time permits. This work stuff gets in the way of Model A mechanicing.

[wensum]

I had an all new distributor from Snyders and always set the points gap on number one whilst checking the timing.
The engine ran poorly until I discovered that the points gaps on the other three were way out,
Either the cam had been ground off centre or miss-shapen
A new Stipe cam solved the problem and made a big difference.
Keith

[George Miller]

Originally Posted by Mitch//pa

Quote BobC ''The higher the compression the higher the voltage necessary to fire the plug"""

Bob can u elaborate
Are we talking flameout?

Yes that is the way it works.

[Mitch//pa]

Originally Posted by George Miller

Yes that is the way it works.

Do you think we have to worry about flame out with the compression ratios of the A?