Misfiring.

[simmitc]

Symptoms: The car starts perfectly. Runs well for about 12 miles, then starts misfiring. Doesn't stop, just misses when under load. Idles OK. It's now been fixed, but just for fun, what would the other experts think was the cause? I'll post the answer once we've had a few suggestions.

[bmcecosse]

Most likely - condenser - heating up. Could also have been fuel starvation - possibly from vacuum forming in the fuel tank due to unventilated cap..........

[xpress]

plugs old and needed regapping?

my other guess is new rotor arm?

[beero]

Your wife gets fed up with the weight of her handbag on her lap after 12 miles, pulls out the choke knob to hang her bag up!

[MColes]

Your wife gets fed up with the weight of her handbag on her lap after 12 miles, pulls out the choke knob to hang her bag up!

A friend of mine used to own a garage. One of the little old ladies that used to get her car MOT'd by him used to use the choke in her car for exactly that! When he explained that wasn't what it was for she replied "I can't push it in... I'll have nowhere to put my handbag"

[dalebrignall]

timing to far advanced

[simmitc]

I like the theme of the choke, but I'm afraid there's no winner. I swapped the condenser with a known good one. Replaced the rotor arm, cap, and leads with known good ones. Checked compression, vacuum, and timing; replaced the fuel pump, and checked that the cap vent was clear. Finally, I swapped the coil with one from another car. Of course we often joke that it's never the coil, but in this case the fault moved to the other car....

[bmcecosse]

Well - when I say it's 'never' the coil - sometimes of course it IS the coil. Just that too many jump to change the coil before trying less expensive options first. And - modern coils sometimes don't seem to be all that older coils are.......so where possible the old coil should be retained. Are the terminal connections on that coil ok? Not loose in the rivets ??

[xpress]

well done for sorting it out! good checklist you went through! didn't realise that the cap needs to be vented! will check mine is clear. has anyone used an accuspark distributor? wondering if you've seen better mpg? not sure i can going to like checking/gapping/changing points if trying to turn her into a daily driver ..

[simmitc]

Roy, I agree that it is rarely the coil. The "believed faulty" unit appears to have good solid terminals when cold and hot, and shows OK on a meter, but definitely shows faulty on two different cars!

xpress, I've not used the alternative dizzy, but points are OK for at least 6,000 miles, and plenty of us use the cars as daily drivers. Join the club