I took the weber off my 1200 a week or two ago., and refitted the holley 350. After much trial and error, and LOTS of cussing and swearing, It runs like it should. In the very beginning, (at least 18moths ago) It refused to run properly at all. I gave up, and refitted the weber. Then a few months back I had another crack at it. The mongrel kept flooding. After lots of tweaking the reg, and fiddling with the float level, it turned out the brass float had a hole it in. I robbed one out of another carb. It stopped flooding, win.
Then I found it wouldn't run on the main circuit. Si I fitted a pair of monster jets.It ran, but still like arse. Then I was revving it up and looking down the carb, only to see that the accelerator pump discharge nozzles were piddling fuel into the barrels.I asked on a few forums arounf the net for advise, and found none.So I asked holley for help. The put me onto a bloke name Scotty Mclendon. He sold me a kit which uses a spring to keep the accelerator pump check needle seated. I had to play arounf quite a bit to get the spring pressure high enough to keep the needle seated, but low enough that the accerator pump actuator arm (wich is spring loaded too) was able to overcome this pressure and discharge gas. Sorted. I also had to externally reference the power valve, so that when the boot is up it, the valve will open. On supercharged engines, it possible for their to be enough vacuum present to keep the valve closed even at wide open throttle. I plugged the port which normally supplies the suck, and cross drilled the baseplate for a tube which is fed from a hose from after the supercharger. I also used the lowest vacuum powervalve they sell. (2.5 inhg)
Next I put a wide band A/F meter on it that a friend kindly loaned me. I set the idle mixture perfectly. I must say it idles much sweeter than it ever did with the weber. Then I changed the main jets, and went for a drive. Cruising at the speed limit, the A/F hovers around stoich. When the boot is hard up it, it richens up to around 12:1. Which is about where it should be. (more or less)
With the bigger carb on, it really goes harder. There feels to be more mid range-top end power. I think that the bigger holes are allowing the motor to fully utlise the cam. In third it nolonger runs out of puff, and pulls hard right through into the high revs. So much so, I think it's blown a head gasket. But sh1t happens.
The weber was really suffocating my motor.