Hate to be a buzzkill, but, to keep your brain working on the real cause, the fuel tank is not designed to hold pressure. It is vented to the carbon canister.

26 minutes ago, Zed Head said:

Hate to be a buzzkill, but, to keep your brain working on the real cause, the fuel tank is not designed to hold pressure. It is vented to the carbon canister.

fair but the tank was being vented through essentially the gas cap and the carbon canister.

one interesting thing to note is 2-3 minutes after putting the cap on with the car sitting off in the garage, i heard what sounded like bubbles/fuel moving/fuel splatting on the ground/etc. i ran to the back of the car and there was nothing on the ground. after a thorough inspection of everything I was going to pull the car out of the garage, I turned the key and the car started up on the second crank which has never happened in the decade+ that I've owned it. it also sounded like the starter was somehow turning faster too.

I did some research and it said with the cap on, the tank was now a sealed system which pushed air that was in the lines up into the evap tank and the starter was spinning faster because the it was no longer pulling the engine against a vacuum.

On 10/15/2026 at 8:29 PM, chaseincats said:

fair but the tank was being vented through essentially the gas cap and the carbon canister.

one interesting thing to note is 2-3 minutes after putting the cap on with the car sitting off in the garage, i heard what sounded like bubbles/fuel moving/fuel splatting on the ground/etc. i ran to the back of the car and there was nothing on the ground. after a thorough inspection of everything I was going to pull the car out of the garage, I turned the key and the car started up on the second crank which has never happened in the decade+ that I've owned it. it also sounded like the starter was somehow turning faster too.

I did some research and it said with the cap on, the tank was now a sealed system which pushed air that was in the lines up into the evap tank and the starter was spinning faster because the it was no longer pulling the engine against a vacuum.

@Zed Head well scratch all of that - looks like you're right again. i really should just stop coming up with my own ideas and listen to you people.

The car began its hard starting nonsense again today so I pulled off the brand new cap and yep - the brand new cap is getting ground down by the brand new rotor. I confirmed this by pulling off the rotor, writing on it with a marker, putting the cap back on and turning it on for ~20 seconds. pull the cap off and yep, the marker's ink worn off in the same spot.

The distributor's shaft has 0 play in it. I could just grind the rotor down with a dremmel, but I mean cmon.

You either have a defective rotor or its not completely seated. Chance are the cap is toast at this point.

Are the cap and rotor of the same brand? Where did you get them from?

Post more pictures. Rotor installed, cap installed.

I remember having a rotor that was loose because the spring inside was weak.

Edited October 17Oct 17 by Zed Head

I made a video here - this might help

I do notice one odd thing in your video. You seem to have the cap on 180 off. I'm not sure how it would be possible if the square metal locating piece is installed. Can't really tell in your video if it's there. The breaker plate screw holds it in place. Maybe it's on the other side and the cap was installed correctly. Can't tell. Part 18 in the image below.

And you didn't tell brand or source. Plus you didn't show it with the spring clamps in place. They can be hard to get on. I used to use a long screwdriver to lever against them from the side to get them to snap in to place. Couldn't get my fingers down there.

Edited October 17Oct 17 by Zed Head
+r

10 hours ago, Zed Head said:

I do notice one odd thing in your video. You seem to have the cap on 180 off. I'm not sure how it would be possible if the square metal locating piece is installed. Can't really tell in your video if it's there. The breaker plate screw holds it in place. Maybe it's on the other side and the cap was installed correctly. Can't tell. Part 18 in the image below.

And you didn't tell brand or source. Plus you didn't show it with the spring clamps in place. They can be hard to get on. I used to use a long screwdriver to lever against them from the side to get them to snap in to place. Couldn't get my fingers down there.

This is the Amazon product I used - the cap and rotor came as a set so you'd think they would function together properly: link here

I never thought to check until now, but since the cap/rotor I pulled off early in this thread was also (very) chewed up, it makes me curious what is going on especially since there is no play in the shaft like you saw in the video.

The distributor is facing the right way as the car runs very well outside of this weird issue. Here is a pic of the rotor installed and then one of cap installed (with the rotor inside of course). The cap fits flush and snugly on the distributor with both of the spring clips clipped. The car is a 1978.

I hope these help:

I would check that the rotor is actually seated completely. Besides having a loose one I also have a vague memory of a tight one or two. Maybe you're just not pushing it down all the way.

If the shaft is moving then you'd also have problems with the air gap. Worth the time to check that while you're in there.

24 minutes ago, Zed Head said:

I would check that the rotor is actually seated completely. Besides having a loose one I also have a vague memory of a tight one or two. Maybe you're just not pushing it down all the way.

If the shaft is moving then you'd also have problems with the air gap. Worth the time to check that while you're in there.

25 minutes ago, Zed Head said:

I would check that the rotor is actually seated completely. Besides having a loose one I also have a vague memory of a tight one or two. Maybe you're just not pushing it down all the way.

If the shaft is moving then you'd also have problems with the air gap. Worth the time to check that while you're in there.

I just checked to make sure it was all the way down (by LGHTLY) knocking on it with a hammer, and there isn’t any shaft wobble (phew!) shown in the video.

Regarding what you sent, I adjusted that when I got that new distributor a year or two ago so that should be good.

Do you think both caps and rotors could have been to blame?

It's hard to tell much from your pictures. I'm not even sure that a little rubbing would cause running problems. Seems like if it was bad that you'd hear a buzzing noise from the distributor as the rotor ticks past each electrode. "Red herring" might be happening here.

1 minute ago, Zed Head said:

It's hard to tell much from your pictures. I'm not even sure that a little rubbing would cause running problems. Seems like if it was bad that you'd hear a buzzing noise from the distributor as the rotor ticks past each electrode. "Red herring" might be happening here.

That would make sense if it wasn’t for how much it chewed up the old cap after a few hundred miles, no?

Edited October 18Oct 18 by chaseincats