Engine sputters then low power when A/T upshifts

[DNK70]

I finally got my '88 Raider running. It's got the 4G54, jet valve elim kit and 4 speed overdrive trans. I have done almost everything on the TO DO list (including a drain and fill of the A/T) except replaced the thermostat, which I plan to do next week. It idles fine and I can rev over 3000 RPM in Park and Neutral with no hesitations or other issues. But, when I try to drive it sputters and sometimes dies when shifting from 1st to 2d. Any ideas on what the problem could be and what to check or do next?

[DNK70]

I finally got my '88 Raider running. It's got the 4G54, jet valve elim kit and 4 speed overdrive trans. I have done almost everything on the TO DO list (including a drain and fill of the A/T) except replaced the thermostat, which I plan to do next week. It idles fine and I can rev over 3000 RPM in Park and Neutral with no hesitations or other issues. But, when I try to drive it sputters and sometimes dies when shifting from 1st to 2d. Any ideas on what the problem could be and what to check or do next?

A little more specific on what happens. It will accelerate slowly in first then when it shifts to second, it backfires (not a loud band, more of a loud puff/pop out of the carb), sputters, power drops off near idle (sometimes dies) and won't acclerate hardly at all, if I back off the gas and add it again slowly I can usually get it up between 1500-2000, but that's it. If I try to give it more gas after that it starts to pop and sputter again.

[geezer101]

Check the basics first. Look at your ignition/distributor set up. What the coil is like, how the timing is set. Check for vacuum leaks. This is a process of elimination so it might be a while before you find the culprit (especially if you've had it all apart and have just got it back together)

[DNK70]

And I'll be pulling the plugs tomorrow to check them too.

[DNK70]

New coil, plugs, wires, rotor, cap and timing at 5 degrees BTDC. I haven't found any vac leaks YET, but we all know that doesn't mean there aren't any. I did a power braking test (put it in drive with the brake on and tried to rev it), but it wouldn't get past 2,000 RPM. I think that most likely rules out a transmission problem (fluid was clean and pink too). It has a "Weber" carb (really a Solex 34) and after watching the awesome video Brad posted, I went back and did the initial carb setup. I had to back the idle mixture screw out almost 4 turns to get best idle which is around 1100 RPM, and only had one turn in on the idle speed screw. So I think I might have an idle jet that is too small. I took the top of the carb off, sprayed everything liberally with carb cleaner and removed all the jets and air correctors to give them a good bath. Didn't see any obstructions, but they were dirty. I have all the numbers now, so I plan to give the tech guys at Weber Carbs Direct a call tomorrow (if they aren't off for Labor Day) and see what they say. After I put it back together, I'll give it the Seafoam treatment and maybe a hillbilly tune up and see how it goes. I'll post an update after all that.