Crazy thing with a new distributor cap

[HAFROD]

So my El Camino has had a slight miss at idle. I drive it every day so I know when somethings up. I pulled the cap with coil in it and swapped it with another cap/coil I had here. No more miss. I noticed when I put on the cap that it wobbled. The locking tab was in its slot but the cap would move a little. I installed it anyway. So I took off for the hospital this morning and it sounded like a rocker arm clattering. Came back home and it is the sparking under the cap. I had an accell cap here that was new and it locked down better. Fixed it. I've messed with small blocks and HEIs all my life. This was a first. It was a Parts Master or Master Pro distributor cap from O'Reilleys.

 

[565bbchevy]

Well I am guessing just a inferior quality product.
I had the opposite for my Regal with a 307 I stole the rotor, cap and coil off a complete HEI SBC distributor that I bought new for under $40 off Ebay and surprisingly the red cap and rotor are very nice with brass terminals and along with the coil work great on there it would have almost cost me that much just for a decent replacement cap and rotor from Autozone.

 

[Bonnewagon]

I have seen plenty of brand new caps and rotors be bad. It drives you crazy because it can't possibly be the new part, could it? Yup. Someone smarter than me once advised: when something you changed doesn't work- go backwards putting stuff back until you find the bad part.

 

[SoFloG]

I think I'm having the same issue with a brand new professional products hei. Slight misfire at idle and doesn't want to stay running under 1200 rpm. Changed the plugs, on the second carb, and the timing is perfect.