M series metering rods are correct.
We NEVER read plugs to determine rich/lean, impossible with this new fuel.
We tune for results, smooth off idle, and at light heavy throttle, thru transition, etc.
RPMS have NOTHING to do with the movement of the power valve, it moves with throttle angle/engine load, which you can not duplicate without actually driving the vehicle.
A stronger spring lowers the cut-in point, but seldom the correct course of action to tune for light part throttle issues. The PP spring is for tuning heavy part throttle and quick movements of the throttle which require increased fuel delivery. The accl pump also helps these scenarios.
For light/part throttle operation and light load tuning do it with the APT system. I prefer to determine the correct jet size FIRST, by doing some heavy part throttle driving, then go back and fine tune the part throttle/light load range with the APT.
If you can't come in range and the jet size is fine, they go with smaller metering rods (assuming too lean). If it's rich, go with larger metering rods.
The camshaft you are using is not a user-friendly cam. It may be contributing or even causing the low rpm issues. I've had a number of engines in here with multiple issues, and the XE cams have been a common denominator more times than not.
The are on 110LSA, with short seat timing events and excessive opening/closing velocity for the valves. "Chop" or irregular engine operation below 2000rpms is not uncommon with them, and is caused by the early intake closing point, combined with the short seat timing/quick valve events (bouncing the valves on the seats and some noticeable "reversion").
This certainly produces a nice sounding idle, if you like a little "lope", but I've seen those engine run rough up thru and past 1500rpm's or so until things would smooth out, with the only real contributor being the camshaft.....FWIW.....Cliff
