My old 1964 413 Chrysler has this weird problem where even with my foot to the floor, it won't go past 60 or 65. It'll downshift and upshift just fine and will rev high and low just fine, it just lacks power and runs hotter than normal when doing so. Foot to the floor at 60, it downshifts into 2nd and RPMs go up as expected, no higher acceleration and engine gets hot, also does have trouble getting to freeway speeds. One guess I have is that the brakes could be grabbing slightly just enough to cause this problem, another is a bad thermostat.
Another problem I have is that my Idle screw keep slipping out and keeps getting caught on the secondaries, causing them to not only be incapable of opening but me to have almost no throttle at all, as this will make it so I can't press down the pedal hardly.
I'm not sure if both of these problems are related, but it wouldn't surprise me if they were. I'm still trying to think of a way to keep the idle screw where it belongs so it doesn't come out when I'm driving. Anything else I'm not thinking of? And yes, my transmission fluid is full, though could this problem be caused by overfilling of the trans fluid? Just curious.
Check basics like dwell, timing, condition of plugs. Check for an exhaust restriction. Bad thermostat, bad water pump (rusted or loose impeller), clogged radiator, bad fan clutch if so equipped, collapsing lower radiator hose, retarded timing can cause overheating. I don't know what carb is on that engine but most I've worked on have springs on the mixture screws to hold them in position.
However, if revs are going up but the car is not moving any faster your transmission is slipping. Those old Torqueflites are very robust but we're talking about 60 years old here. Fortunately unlike most of today's transmissions rebuilding those is feasible if needed,
