1964 C60 with a brand new 292 bored .040 over with 120 miles on it. Rebuilt with stock manifolds and cam. I had purchased a rebuilt Rochester B but it had its own issues and refused to throttle back from ~2200 RPM. So I took the old Rochester that seeped, slapped it on, and the truck ran great. Barring an accelerator pump that kept off the line acceleration boggy, I could hit 55 in no time and maintain it at %80-85 throttle. Then cruising back one day I discovered that to maintain 55, I was suddenly at 95% throttle, and at 100% throttle I would get misfires. This progression continued util 95% throttle = 45mph, and then ultimately 40mph as I made it home. Front plugs were blackish grey, rears were white.
First thing I did was check all breaks, and readjust when I found a dragging rear shoe. No change. Then I pulled the old Rochester B off, whipped out the rebuild kit, qued up the videos from Mikes Carburetor Parts, and went to town. Power piston was seized, accelerator pump was shot, but everything else looked good. Thoroughly cleaned before reassembling alongside Mike's video, mimicking exactly what he spoke to. Slapped her back on the engine, warmed everything up, readjusted mixtures by ear, and low and behold a world of difference at idle. But, top speed was now 30mph. That 292 would roar and scream like a scaled cat from 1Lo thru 3Lo, start to wind out in 3Hi, and then fall flat on its face in 4. No coughing, no sputtering, just flat out foot on the floor going nowhere.
Next thought was fuel pump. Finally got it in, installed, and zero change. This time though, the carb was flooding, and this is where it gets interesting. Floats were set at standard 1 9/32 with 1 3/4 drop and the carb was slobbering fuel everywhere, turning in idle mixture all the way netted zero change, and any amount of choke on a cold engine would flood it and prevent start. I got it running with pedal on the floor, no choke, and crank. With the pto for the dump bed engaged for an engine load, I was blowing black smoke.
Off comes the carb and back to the bench again. First thing I check is my floats which are at spec. I pull out the old floats and check them. Lo-and-behold they are set at 1 13/32 with a drop of almost 2. I check the accelerator pump circuit which is working correctly, all ball valves are functioning proper, the needle and seat are sealing and there is no blow by of the needle and seat gasket. Without adjusting them, I reassembled with the old floats at the above spec and reinstalled. I am no longer flooding, I have regained mixture screw control, and no more black smoke. But, still stuck at 30 mph. Frustratingly, I advanced the distributor a tad which makes the engine run less smoothly, but I can now hit ~38 and have some guts for the 4Lo shift, but top speed is 45mph with foot on the floor and it takes 60 seconds to get there on flat road while empty.
I once again take everything apart but find nothing wrong, no indication of clogged ports, and no reasonable explanation. I slapped the spare carb back together and it still for whatever reason wont drop under 2200 rpm at idle, but that's a different topic all together.
Other things to note:
Rear axle and brakes are vacuum operated and functioning fine, thus no indication of a vacuum leak in the system (will need a gauge to verify but don't have one on hand)
From a 30 mph roll, this truck will coast a full mile and still be moving 10mph, so it isn't driveline, wheel, or brake related
The truck ran like a top until it slowly progressively just started loosing top end for no apparent reason
Brand new fuel filter with ~25 miles on it, zero particles inside of it, and no indication of any clogging
During the rebuild, I emptied the gas tank, flushed it with some seafoam, and then fresh gas, and then sealed it again and its only seen gas and Stabil since
The original Rochester Airhorn is slightly warped, but not bad enough to cause issues, just a slight weep of fuel when operating
It has to be a fueling issue because I cannot even come close to the RPM I know this engine can do in the high gears, the RPM is was cruising at just a few weeks ago
I am quite frustrated at this point and looking for any input others may have on what is going on. At this point I am not above putting these Rochesters in a cannon and firing them over the horizon and out of sight.
