Quote:

...pipes were Stock with 2 baffles removed (Chevy 605's). I think the BC Bombers are about the same as far as back pressure.



Well, I'm not so sure that is true, although it is certainly possible.

I also have no idea what size FF drilled out the slide air ports to, or what springs he used, but let's presume for discussion that the ports are now approx. 3mm +/-, & presume that whatever he did to the springs are now sub-optimal.

All other things equal (& in practice they never are) the 904 kit would tend to increase vacuum all by itself, as compared to a stock bore motor. Drilling the air ports (too much) & going too short/light on the springs would only make a transitory lean issue worse.

One low cost thing you could try that ought to improve off-idle driveability RIGHT NOW is to replace whatever slide springs FF installed with a set of OEM slide springs, for starters. The OEM springs can be tweaked, but you gotta know what you're doing, have a reliable means to measure it, and have a reference point before you make more changes.

You also really need to confirm which needles are in there now - although you could speculate & act on the speculation, you really need to actually check the 4 digit code to know what you are dealing with. Once we know that then I'll have a recommendation that will likely get you closer before your next dyno run. That's an easy top-side check.

If you can get any of the other data that I asked about that would help too.

IMO the pipe change alone is a potential game-changer for the mains, but you'll either need to install an A/F meter or go back for another dyno run with the current pipes to verify. BTW, the last time I was on that dyno (2010) the dyno's A/F meter crapped out, however that should have been fixed already.

If Bill H does the test ask him to also check the AFR at idle, light-load cruise (whatever speed that is for you), & simulated hillclimb.