So I got sick of the weather changing constantly (Michigan) and me playing guessing games with my C10's Holley. I rebuilt the motor last summer, it runs great, but when the weather changes (humidity, temperature, atmospheric pressure, proximity to Saturn), I'm always spending half a saturday trying to make it run decent again. I guess not re-installing all the little thermal vacuum switches, air pump, and other related things, (usally refered to as "emissions" equipment, but a lot of it is there for drivability reasons too.), is the cause of my woes, but alot of it would have been very difficult to reinstall with the non-emissions intake, holley 4bbl (instead of tire old qjet 4bbl that was stock) and various other things I used when I built the motor. Anyhow, so today I installed my new HFI system on it! Human Fuel Injection. I'll never attempt to tune another carb without this system! Human reads sensor/gauge, human makes adjustments to fuel system. OK it's an electronic Air/Fuel Gauge (clicky) with a generic GM 80's o2 Sensor (clicky). Now I can see EXACTLY what the heck was going on. Today, it was massive bogging (dieing is more like it) during acceleration. I would get these bogs, and I'd try different pump shooters or cams with seeminly no change, my trusty gauge told me it was a way way to lean bog, so I change shooter from 25 to 35, a huge change, one the books tell you never to make, and magic, gauge sticks right in the middle during acceleration now, and no more bog. Biggest shooter I had was 31 at the time, and I still had a bog, but the I noticed it didn't drop off to lean quite as fast with the 31 in there as it did with the 25 in there. Local parts store happen to have a 35, so I bought it and popped it in there. Sweet. But without gauge, there was no noticible difference in the bog and my head was telling me well, 31 is a huge jump, I should see a change, so I must have gone to far, and I go back and try a 28, still a bog. Anyhow, I love this setup, $60, so fairly cheap too. Since the sensor is cheap, it doesn't work until the engine warms up a few seconds, if you bought the expensive $70 wide band sensor, it would work better. But for tuning purposes, the cheap one is just fine. So if your scratching your head during carb tuning, this will help.