17080292

[von]

17080292 1980 Chevy truck 350 carb, single main air bleed, going on a mild performance 350 in a Chevelle using recipe #2 for the rebuild. Fine thread mixture screw holes are small, around .078. Should they be drilled larger and if so what diameter? Engine is stock except for cam which is 214 deg int and 224 deg exh duration @ .050 lift and 112 LSA.

[novadude]

The last SMAB carb I did that was similar to your 17080292, I used 0.086" on the idle mixture screw holes, .059 LIAB, 0.067 UIAB, 0.052 IDCR, 0.035 idle tube, 0.072 Idle air bypass.  Plenty of control over the idle mixture. 

This was on a 355, 9.6:1, 217/225 @ 0.050 cam on a 108 LSA, so more overlap than you have.  The same carb with no changes is on a Chevelle with a 9.2:1 396 running a small 204/214 @ 0.050 cam.  Works well on that engine too.  I think you will be fine at 0.078".

[von]

Thank you.