The SR43 engine fit right into the SR41 frame.
Carbs/airbox, everything fit with no problems.
I used the flywheel, stator, and ignition coil from the SR41 engine. This all bolted up inside the left case from the SR43.
A small adjustment had to be made for the decompressor linkage in the cylinder head. The SR41 uses the manual decompressor and the internal part of the shaft is shaped just a bit differently from the automatic decompressor on the SR43.
The 43 uses a shorter shaft with a smaller weaker spring.
When I tried to start the bike, the decompressor (once activated manually) would not reset and allow the valve to close.
I transplanted all the parts from the 41 engine into the 43 cylinder head (everything fit without difficulty)
The cylinder head of the 43 had no hole tapped to support the cable holder bracket from the 41. The head for the 43 still has a large boss cast into it so it was a simple matter to drill and tap a hole to support the cable bracket.
Once this was all finished, the bike started easily and settled into a nice even idle.
Whew....after a weeks work, I was relieved and excited.
Tomorrow I'll finish routing some wiring, attach the bodywork and go for a ride.
........Next, the rebuild starts on the SR41 engine.