Bucking Slightly at Cruising Speeds

Posted by Joe On 2024/7/28 14:48:32

Hey all - wanted to get some takes on this. Had my 23rd series for its longest drive today since I've had it, about an hour and fifteen minutes. Mostly 50+ mph driving, about 86 outside. Not CONFIDENT on the engine temp, but stays about 5/8 of the way to H (I know, I need a proper gauge). A little background:

- 327 w/ Ultramatic
- Fuel: tank is brand new w/ vented cap; lines are relatively new, mechanical pump moving about 3.75 psi at idle, checked lines for leaks/kinks (possible air intrusion - nothing found). The carburetor (WDO 643-SA) has the float set per the Daytona rebuild kit instructions (3/16" w/ their float valve). Metering rods and and anti-percolator valves set per the Carter instructions (metering rods adjusted with the proper T109-113 tool).
- Spark: vacuum advance and distributor were rebuilt in the past 250 miles; plugs, wires, condenser, points, coil are all fairly new. Points gap set to .015". Car is 6v+. Initial timing verified at 7 degree.
- Intake: replaced oil bath filter with paper; no noticeable difference or performance; heat riser is free; no vacuum leaks found
- Exhaust: it's exhausting

The issue: after accelerating to cruising speed and I back off the pedal, 50 or so mph, the car has a tendency to buck somewhat. It's not aggressive, and it doesn't sound or feel exactly like the engine is actually cutting out, but feels like you're going over a wavy road. If I depress the accelerator, either a little or lot, the engine just goes and it all smooths out. It's not always there, but enough to be generally kind of annoying. It also only does this once it gets to operating temperature, but it's been an issue for a while. When the engine temp is below the halfway mark, operation is smooth at all speeds and conditions.

My question - is it something in the carburetor that can cause this issue (should I revisit the metering rods?), or is my transmission slipping? I don't know what the transmission (either in the high range or direct drive) would feel like if it was slipping. The transmission is in relatively rough shape compared to the other mechanical elements of the car - very leaky (I do verify it's full before every drive), and it has no low range (behaves like it's in neutral), so I would think it might be suspect, but I'm not sure.

Any thoughts on what I might be chasing here? Thanks in advance!