Happy New Year!
I’ve recently brought my NSR250 back on the road, but I’m struggling with some persistent running issues.
The bike was "pieced together from a mountain of parts," and since I'm using an MC28 chassis with a mix of MC21 and MC28 internals, I suspect major incompatibilities in the intake and electronic setup are causing the trouble.

My Current Setup:
- Engine: Early MC21 wet engine with MC21 flywheel
- Electrics: PGM-III unit (MC21) and full MC21 wire loom.
- Carbs: MC28 carburetors with MC28 TPS.
- Jetting: MJ 145 / Power Jet 80 / Pilot 42. (all on both cylinders).
- Air System: MC28 solenoid system and hoses.
- Airbox: Original MC28 airbox.
- exhaust: original MC28 derestricted

The Symptom: The bike isn't running cleanly, especially in the transition zones and during deceleration (stalling issues when quitting throttle.

The "Back to Basics" Plan: To eliminate the guesswork, I’m planning to revert to a full MC21 intake side to match the PGM-III:
- Switch to MC21 TA22B carburetors (including the matching MC21 TPS).
- Install the MC21 solenoid hose assembly
- Switch to an MC21 airbox (wire splice performed, lid modified/drilled).
- then rejet for new components

I have two specific questions regarding the compatibility of my current "mixed" parts:

1)
TPS Signal: I’ve read that the MC21 and MC28 Throttle Position Sensors have different resistance ranges.
Can the PGM-III actually interpret the MC28 TPS signal correctly? I'm worried my ignition and RC-valve mapping might be receiving garbage data.

2)
Solenoid System: My understanding is that the PGM-III is designed for the MC21 hose routing, which relies on physical air jets inside the tubes.
The MC28 system seems to rely on a different duty cycle/logic from the PGM-IV. Is it correct that the PGM-III simply cannot control the MC28 air system properly?
The solenoid valves themself should be interchangable, since on CMSNL the part number from MC21 and MC28 are same.

Am I on the right track by standardizing everything back to MC21 specs to match the PGM-III?
I'd appreciate any advice or confirmation from those who have dealt with these hybrid setups before.

Kind regards from Germany, Felix