Rough running suddenly

[st63]

Interesting issue cropped up yesterday....my stock P-12 coupe with the flat six usually runs like a top, but after being stuck in traffic for a couple of hours yesterday (lots of idling, stop and go at 5mph) it started to run rough, as if the choke were suddenly engaged.  I'm thinking the plugs may be fouled from the excessive idling, but I wonder if anyone else has had a similar experience and if there is something I should check before the plugs?

[DonaldSmith]

Coil going bad and overheating?  

Electrical connections loosening because of metal expansion?  (Star washers are recommended at electrical posts.)

That's the extent of my wild guesses.

[st63]

Good guesses, and also worth checking, thanks!

[_shel_ny]

,,,

Edited November 8, 2014 by shel_ny

[55 Fargo]

Why guess???? Start the systematic process of elimination, in order, rule out any causes. let the forum know your findings and subsequent solution(s)...Good Luck

[Joe Flanagan]

A vacuum leak is also a possibility. 

[Don Coatney]

Follow the very good advice of Fargo-go-fart and do it systematically.

[Reg Evans]

Just curious......did you re-start it after it cooled down and if so did it run better ?

[st63]

Not a fan of guessing...just a figure of speech. Just wondered if anyone had any ideas of what to check first. I let it cool down overnight and it still runs a little rough. So far changed the plugs out, checked the vacuum lines, checked to make sure the choke is free, and it's still rough. It runs almost as if the choke were engaged.  I'll keep going through it bit by bit and will report back. 

[Don Coatney]

Are you getting any smoke out of the tailpipe? Any smoke visible with the engine running and the oil fill pipe cap removed? What did the all of the plugs look like? Brown, white, black? With the plugs removed did you do a compression check? Have you inspected the distributor cap inside and out? Any signs of moisture and or cracks? Spring loaded plunger in the top of the cap in good shape? Rotor contact area clean? What do the points look like? Burned contacts, gap setting etc.? Is the small wire in the distributor intact and not grounding out? Connection points on all wires secure?

 

What are you using for a carburetor air cleaner and is it clean and free flowing?

[st63]

Thanks Don. No smoke from the tail pipe, faint white smoke with the oil fill cap removed after shut down (though it's been like since since I've owned it without the rough running issue) Compression checks out ok...plugs were light grayish...seemed normal, but I changed them anyway.  Haven't yet gone through the distributor...that's next on the list.   Air cleaner is the stock oil bath type.  

Edited November 9, 2014 by st63

[Chrisdabarber]

Do you ever figure out the problem? My flat head started doing the same thing after I got off the highway it started sputtering I noticed the wire to my coil from dizzy got loose replaced it and plugs still running ruff

[st63]

I never pinpointed exactly what the issue was....I finally just did a complete tune up and replaced the plug, points, condenser, rotor etc...and that

seemed to cure it.

[Tones52]

For me it turned out to be the accelerator pump check ball in the carburetor came loose. Hope you find the source of your problems and post the results.

[deathbound]

Nice looking '41.....would like to see it in person at 1 of our "So Cal gatherings".

[fedoragent]

Nice looking '41.....would like to see it in person at 1 of our "So Cal gatherings".

I'd like to do that as well!  I live in the same town as this gent!  Don't forget the Pasadena Drive on Dec 31st.  Also, the Socal Get Together on January 17th!

 

FG.

[st63]

I plan to be there for the Pasadena drive on the 31st along with some of the other local Plymouth guys...should be fun!

[choptop40]

Check vacuum leak , my pal in NY would take the top plate off the carb and use fine drill bits to ream out the venturies , would run like a top....took him 5 minutes....gas varnishes and clog the ports.....best wishes

[fedoragent]

I plan to be there for the Pasadena drive on the 31st along with some of the other local Plymouth guys...should be fun!

Awesome!  I'll be there.  Hopefully with my car if the new body mounts are in by then.

[dpollo]

I think I would do a compression check to rule out  (or confirm) a leaky head gasket  also look for oily  residue in the radiator.

Then  check the vacuum to see if any leaks have developed in the intake or if the valves have decided to be sticky.

If the  vacuum gauge flutters, try pouring a bit of oil or a diesel/oil mix down the carb.   Modern fuels do not provide much lubrication

for valve stems.  A bit of 2 stroke oil in the fuel often helps.   maybe as much as a quart in 10  gallons at first.