6psi at idle on the hose really will not tell you much. You need to see what it is at cruise speeds and WOT and make sure it holds at least 5psi there.

Since you have had recent fuel system work pull both of the needle and seats on your port side carburetor and inspect for the tiniest grain of dirt and blow them clean. I had similar issue after replacing fuel lines and pumps, one side would pop when the secondary would open and discovered a grain of dirt that got stuck there in the needle and seat. Free fix, so won't hurt to try.

Just got back. Was able to run with hatch up and it’s firing back up through the carb - black puff of smoke out of the intake. I’m going to swap carbs and see if the problem follows…..

What did the fuel pressure do while running???

Never noticed a dip in pressure at speed. Again, the gauge is mounted on the carb so I was monitoring with hatch up running in the bay.

the carb is black from the backfiring so I pulled it and tore off the bowls and metering block. The rear bowl had some stuff in it. I cleaned it out and will put a new power valve in tomorrow before I reassemble….

Squirt thru every orifice with the red tube both ways. Watch your eyes. Then finish iff with compressed air thru each orifice both ways.

Yep, B12 is brutal on the eyeballs. Got a reminder of that earlier today.

Billy had more than one valvetrain issue with those motors. If you can't narrow it down on the outside, pull the valve covers off and look for issues.

Have you checked ign timing and verified the marks on your balancer is correct?

Pulled carb and cleaned. Didn’t find anything OBVIOUS, but there was some gunk in the rear bowl - but not a lot. Noticed someone had used Teflon tape at one point on the regulator so pulled that off and used pipe sealant. I guess there could have been something more significant that I didn’t see.

ran about 10 miles tonight at 3500-4000 and didn’t have any issues. Still not convinced, but we will see.

got the rear float set a bit high. It’s at the top of the sight glass so I need to correct that, but ran out of daylight to go back out….

i will say that I dumped a lot of the fuel out of the carbs before I pulled the bowls so there could have been something in there that I just didn’t see fall out. Will test again Thursday….