Tyree

Something to check. I see that you think it may be a fuel problem. When I put the efi on the flathead I had a problem that came and went not all the time and was noticeable when I went around corners.
At first I had no CEL no way of data logging and I hooked up a monitor to the o2 sensor and saw it was running rich.
I finally figured out it happened when I filled the tank. I thought it was a good idea at the time to hook up the purge line to the emission outlet on the tank. This was a straight link without a purge canister. So full tank going around corners vac line sucked fuel and caused flooding. FIX.... disconnect this line.
It maybe a long shot but check if your problem occurs when the tank is at a particular level, it could be a pick up level?
I had people telling me all sorts of things, wrong octane rating, timing, coil, spark plugs, my age, wiring, it just wasn't going to work, put carbies on it, fuel filter, fuel pump.......

MOC