Hi folks- I have an injected 122, engine and wiring swapped in from 72-73 142. The engine that came with it started and ran normally, idled fine, but was worn out and needed replacing. I swapped in a good running B20 from a '73 (I heard it run, idle, warm to proper temp, etc..) I have it all plumbed up, but upon starting , the idle goes through red line immediately... I can't find any vacuum leaks. I didn't swap the "brain". Any suggestions? Thanks!

The 73 manifold will have a port for the brake booster and a port that has a restriction for the breather. If you swap hoses and have the unrestricted port connected to the crankcase, it will rev like you describe.

Thank you for that advice. I did indeed make that mistake, had the flame trap run to that one. I replaced it with a restricted nipple... but no change. so I blocked both nipples. no change. I don't think I overlooked any other open ports. The butterfly looks completely closed, and it does respond to throttle. I'll keep digging for other leaks. I don't think the problem is in the positioner, because it ran fine before it was yanked.

Manually push in on the butterfly to make sure, better method than just looking. Maybe it is gunged up inside or something?

The only thing that can cause this is unwanted air getting into the intake, and a fair amount of it if it's revving that high. This suggests the throttle is somehow hanging open. I'd start by double-checking that part of the system.

thanks a lot! i'll start digging.