'66 289 distributor problems

so i finally got my '66 coupe started and running halfway decent (289 2brl w/ C4). but i've got a weird problem with the distributor... cylinders 1 and 5 don't fire unless there is some pressure (like pushing on it pressure) on the vacuum advance... they all fire just fine when the vacuum advance is pushed all the way over up against the upper radiator hose... which is "fine" (i'm going to be selling the car), however it's got a lot of advance when it's like that...

i imagine the only fix is to replace the distributor with a rebuilt one? i've popped the cap and everything seems to be tight inside. any ideas?

distributor is original w/ single set of points. other than this issue, the car runs really pretty darn good all things considered!

i'm not used to this low-tech stuff!!

i've got the gap set to the book values and tried to scuff them up a bit to make the surfaces flat. will do!

thanks for the advice.

Problem isn't a lack of advance (it's probably overly advanced right now).

Maybe I wasn't clear enough...

When the distributor isn't butted up against something or I'm not putting physical pressure on the vacuum advance diaphragm housing, cylinders 1 and 5 do not fire. If I press on the vacuum advance diaphragm housing cylinders 1 and 5 magically fire and then you let up and it dies (but will immedietally restart and run fine despite 1 and 5 not firing).

Seeing as this part interacts a bit with the plate for the points, my guess is that like you all said, the points are probably shot.