40's would be fine for a rev range quoted.
Even the hottest of A15's would only require chokes of ~ 36mm size. 32mm - 34mm would be perfect for an all rounder.

Perhaps valve clearences,
IN .30mm (11.8 thou) sounds too tight
EX .35mm (14thou) sounds right
I have run .35mm (14thou) on both IN +
EX on hot motors with success, but don't
ignore instructions on your cam card either.

The specific rev range makes it a bit more
mysterious, almost like the carbs are not
making one of their transitions smoothly

Intake Reverb is usually assosiated with big
overlap on the camshaft, what lobe centre
is it?

just a thought

Edit: Are 40mm carbs big enough for what
sounds like a decent A15? What size chokes
are you Running? Could the thing be running
out of air at the top of its rev range?

Are the valve clearances correct. I had an A14 that did the same years ago, turns out we were using the wrong gaps. You said you;ve just run the motor in,now everythings settled down,maybe the clearances are down.

Video link

Took a little video, you can hear it top of 2nd gear right before i let off...

Hey guys,

My built A15 is now fully broken in, seen a few track days and ran a 15.1 shifting at 4500rpm, and generaly runs beautiful under 6200rpm in my B110 4door..

Now comes the problem, as soon as I try rev her over 6300 I get an odd sound, almost like a missfire/reverbaration/ valve bounce and she stutters slightly then clears up and then at 7000rpm will not rev any higher, almost like a rev limiter.

in the A15 I have 11.5-1 comp, 280deg cam (.3mm intake and .35mm exhaust clearance), tomei dual valve springs, Tomei M-spec port layout (copied from one of the A13 touring motors) normalish header, 52mm exhaust, pertronix dissy pick up, MSD blaster SS coil, dual DCOE40's and a nice 3kg cromoly flywheel...

I have tried timing changes, plug changes (everything from range 6 to range 8) as well as jetting changes from 10.5-13afr at WOT, nothing seems to change the sudden sound at 6300rpm then total drop of power at 7000rpm

Here is the million dollar question:
1. Exhaust back pressure is to high
2. some form of intake reverbaration
3. Faulty pertronix?

Any idea's guys?