I have an off-idle hesitation (bog) in my new 489 BBC engine (here's the build specs:
http://www.chevelles.com/forums/showthread.php?t=206196

http://www.tennesspeed.net/forums/sh...light=chevelle (http://www.tennesspeed.net/forums/showthread.php?t=48823&highlight=chevelle)
Could it be the transmission? It's a stock TH350 (3.08 rear gear) with what I assume is a stock TC (which I'd like to make last until winter). It stumbles from a take off and then goes on strong (hard not to break the tires loose). The carb is new and was set up by a local shop (Unlimited Performance) (they also set the timing). The vacuum adv is not hooked up due to the timing going too high with the vacuum adv hooked up.

I changed to a 43 pump nozzle ...that helped a bit, but the hesitation is still there. Edelbrock recommended a 116 primary jet, but I haven't done that yet.

check the condition of your advance plates/bushings/springs under the rotor. a $10 mr gasket advance kit should cover these items. not a fan of plugging the vacuum advance on a street motor myself. tells me something is not right in that dist. "timing going too high" ? I just dont understand. my new 496 is running total timing at 36 deg. initial 18 deg. vacuum plugged. this is with a comp cam xs290s solid lifter cam profile. had those "bog" issues with my old 396 in the past. the advance kit fixed it.

I agree on the timing - might want to post what it is at initial and total - there are ways to adjust both so you get the best of both worlds.

FYI, I'm running about 26/27 initial timing, total of 37, vacuum advance plugged.

Your jetting seems WAY off to me. My 489 has an 82 or 84 jet in the primary, I have to think a 116 is just going to kill your plugs - you should pull them and see just how black they've become as confirmation. Don't remember what shooter nozzle I have in the front. Which color accelerator pump cam are you running?

EDIT: I see your specs, you're running a 750 carb, I'm running a 1050 - that could account for the jetting difference, I'm just not sure.

just to follow-up, I switched out the stock torque converter for a 3500 stall TC and a built TH350. The hesitation is 100% gone.