For a long time I've suspected that the engine was running rich. We're talking about taking the Jeep to Colorado and points west this summer, and at seven or eight thousand feet I feared that it would be WAY rich.
My original plan was to swap on a Motorcraft 2150. I thought that I could cut the 1-barrel top off the intake and weld a 2-barrel plate on but, with the exhaust passages for warming the carb, that proved impractical. (Thanks to Dux4Life, I have two MCs to choose between. If anyone has an unwanted 2-barrel manifold . . .
Instead I decided to fix up the Carter YF, seal the manifold leaks and make the best of it for now. As mentioned in another thread, I now have the Jeep high-altitude jet and metering rod for the YF, so the mountains should be friendly territory.
The exhaust manifold was warped 0.050", so I sent it to an automotive machine shop to be surfaced. The face of the intake that mates to the exhaust was also warped, but the milling machine fixed that. I put it back together and after about five hours of run time re-torqued the bolts and got a quarter to half turn on every one. The leaks aren't likely to come back for a long time.
While it was apart I also made a linkage to control the heat riser butterfly. The thermostatic spring had rusted off years ago, so the butterfly had just been flapping in the wind. Winter warm-up seemed to take forever.
The big change is an AutoMeter air-fuel ratio gauge. ($234.00 from Summit, shipping and a $20.00 coupon included) This is an amazing piece of technology. It uses a Bosch broadband oxygen sensor screwed into a bung on the exhaust pipe just below the manifold. After about thirty seconds of warmup it displays the ratio so sensitively that after going over a sharp bump, the needle bobbles for a second as gas sloshes around in the float bowl.
The good news is that the carburetor seems to be doing just what it should. At light cruise, 45 to 50 MPH, the ratio is about 15.5:1 and as high as 16:1 around 40. Full throttle it drops to 13:1 and goes lower as engine speed increases. By the consensus of what I've found on the net, that's pretty good.
The worst I've seen is that it doesn't handle throttle position changes very well. Opening the throttle produces a brief lean blip followed by a very rich one before it settles down. Closing the throttle produces similar wild swings, but at any steady position the mixture seems to be pretty good.
The dial is a poor match with the rest of the gauges, but that's of no consequence.