Another Model A mystery

[700rpm]

My Tudor started misfiring badly in early December. It had sat for a couple months, after running a 100-mile tour just fine, so I thought it was bad gas and drained it out and put a gallon of real gas in. It still misfired badly. Today it's warm enough to work in the garage, so I go out to see if I can figure it out. I find the trouble: it's not firing at all on #3 or #4. I pulled the plugs. 3 & 4 are wet, as I expected; 1 & 2 look OK. They're old Motorcraft plugs, and should be replaced anyway, so I put four new Autolites in. No go.

I replace the distributor body with a good one after checking continuity in it, and it's good, but ... No go. I reset the gap on my points because though they are new, they are a little wide. No go. Just for ducks, I check my lower distributor plate wire, it's good, so I reset my timing and .... No go. Hmmm. I pull plugs 3 & 4 and check compression. It's good. I pour a couple swigs of MMO into each plug hole and close it up and ... Hey! It runs great!

I don't know why.

[Gary WA]

Stuck valve?

[tbirdtbird]

sounds like it, Ray run 4 oz MMO in every 10 gals of gas

[Mitch//pa]

Stuck valve in both cylinders and good compression?? I think you have something else going on possibly a head gasket seeping coolant in? Just a guess of course without being there and doing further testing

[700rpm]

Mitch, I had thought about the head gasket, which is why I checked compression, but two things convinced me it wasn't that: good compression, and no drop in coolant in the radiator or evidence in the oil (rise in oil level). I likewise suspected a stuck valve, and that also prompted the compression check. Engine has about 4000 miles, oil change every 500, and I did put a little MMO in the gas when I parked it in October, but didn't run it but very briefly after that, so maybe not long enough to adequately affect the valves. I am a believer in MMO, though! And that final addition today seemed to have done the job. Ergo...

[700rpm]

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Originally Posted by tbirdtbird

sounds like it, Ray run 4 oz MMO in every 10 gals of gas

Will do. This is the Tudor, which has never given me any trouble, not the coupe, which you and I have had several comversations about, but which is now running very well. With the Tudor, it does seem likely that there may have been some sticky buildup from the egas. Anyway, it's running fine again now. Just another day in the life of a Model A owner.

[C26Pinelake]

if it was stuck valves in two cylinders how did you have good compression ?Wayne

[Tom Wesenberg]

Marvel Mystery Oil living up to it's name...........it's still a mystery how it works.

A slow to close valve can give a good compression reading at cranking speed, but close too slowly to have compression at running speed.

Never run an engine for only a short period. In the 70's I locked up two of my engines because I ran them for only 10 minutes, then tried to start them 6 months later.

[Clem Clement]

I use ATF: 3 gloops with each fill up. Cheapo I guess (3 dolups = 1 gloop)

[SeaSlugs]

Originally Posted by Clem Clement

I use ATF: 3 gloops with each fill up. Cheapo I guess (3 dolups = 1 gloop)

so how many splashes in a dolup?

[Mike V. Florida]

Sure sounded like dirty points to me.

[700rpm]

Originally Posted by Mike V. Florida

Sure sounded like dirty points to me.

Yes, Mike, I thought about that as I got to resetting the gap, but they are clean.

And Tom, I'm aware of the dangers of not bringing the engine up to good operating temp, and am usually pretty careful about that, but thanks for the reminder. Sometimes I rush things.

[mshmodela]

As you mentioned 3 & 4, are you seeing a spark on 3 & 4 something like this:

[700rpm]

Originally Posted by mshmodela

As you mentioned 3 & 4, are you seeing a spark on 3 & 4 something like this:

Mike, I had zero spark. But I had checked my polarity last year and all is good there. Good thought though, for future troubles. It's not one of the first things I think of in troubleshooting.