so, i purchased a 65 dart yesterday, 225, 3 on tree, 4 door.(period correct daily driver for my 60-66 period built 51 plymouth cranbrook).
it was in turlock, and i live in sacramento, about 130 miles or so. all was well for the first 100 miles., doing 65 with alot more to go.
then once i got just past stockton, it started sputtering and back firing under load.
but idles just fine, it has a new cap and rotor, a new rebuilt carb, msd blaster coil, all previous owner. i replaced points/condenser to no avail.
its seems the severity of how bad the miss/sputter/backfire is intermittent. it was willing to pull 55 barely with very very light throttle touch, too much and itd sputter out,but not die completely. then it got worse. and now still idles well, but sputters and spits/pops revving it even under no load. please help!!

also, pulled cap, and sucked on vacuum advance hose and nothing moved, but moving the plate with my finger seems to take a fair amount of force atleast in terms of vacuum i could produce. is that a reliable test? i know that this could be a cause possibly of my issues.

You might try changing the cap and rotor, sometimes the cap gets enough moisture to cause a carbon track issue.

Richard

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Part of Tyrde-Browne Racing

Im a newbie but have you checked to make sure your fuel isn't too rich? Could be the carb isn't tuned properly.

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69 Plymouth Valiant

the cap and rotor are new, and no the fuel isnt too rich doesnt even smell the slightest of fuel in the exhaust,lean maybe. infact im beginning to look into maybe a vapor lock issue? or accelerator pump?

Check for plugged fuel filter. They will cause a lean mixture starting just at high throttle and gradually at less and less throttle as they plug up.

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Dave

1977 d-200 crew cab ex-army pickup wants it's /6 back
1962 Valiant 2 door, 170, three on the tree
1972 d-100 parts truck
80 volare wagon now a parts car

Have you tried to take it back out on the road today and if so does it run badly right away?

Have you taken a fuel sample, if this car was not driven much it could have bad fuel. This fuel in California sucks, to much ethanol.

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Fast is fine but accuracy is final. You have to learn to take your time ... in a hurry
- Wyatt Earp

Carter or a Holley carburator. (I bet it's a Holley 1920)
DD