40, 140 with a coaster/marbling and 3.5 turns is probably closer. 42 pilots might be okay, but it will suck a lot more gas and you'll need to dial back the screws to find best lean idle. "Best lean idle" first (CARBURETOR SET UP AND LEAN BEST IDLE ADJUSTMENT
), then mains at WOT and a plug chop to set your top end, then shims if necessary to cure lean surging at cruise speeds and tune the midrange. If 4 shims doesn't do it, go to 42's and zero shims, retune from the beginning. Midrange is still mostly pilots, so a bump up there can help.
I run 38/140 and 3.5-4 turns with pod filters, coastered, and wide open slip-on Screamin' Eagle "mufflers". I put that in quotes because they're empty pipes.
I have no lean problems, starts and runs great, and probably the best mpg of anyone on here.
Excerpt from my patented super duper nifty neato jet cross-section charts:
# area % change
38 0.11 1.00
40 0.13 1.11
42 0.14 1.22
# area % change
132 1.37 1.00
135 1.43 1.05
138 1.50 1.09
140 1.54 1.12
142 1.58 1.16
145 1.65 1.21
148 1.72 1.26
150 1.77 1.29
If anyone is going past about +15%, they either have forged internals and a turbo, they're masking some other huge problem, or they're copying bad advice from all the people who like to massively over-jet.
As you can see, there's a huge % change when you swap pilots. That's why we need to play with the screws to fine tune it. Each size bump begins to drop in larger sizes because it's based on diameter, while fuel flow is based on cross-sectional area. We really need about a +15% option on pilots and #138 mains.
Think about how much extra air you're getting and power you're making. Most intake/exhaust combinations won't get more than 5-10% gain, 8-12% if you're doing lollipops, torque cones, etc. to really tune it right. That's the increase in jet size you should shoot for.