Ignition parts (coil, points, condenser) are interchangeable, there are twice as many of them on the 4423 as there are on the single cylinder motor, flywheels and magnetic rotors will also fit.
recoil starters and associated parts will swap around, but the gas tanks are not the same. Filler plug from one will fit both.
Lower shrouds differ between those models so no swapping there.
Powerhead – they are different blocks, and use different methods of induction/carburetors, but share common bore and stroke. Thus, pistons and rods from one will fit the other.
Transom brackets and mid-housing likely the same. Tiller handles and the way they mount are different, the 4423 handle will unscrew from the bracket and turns into a screwdriver when you do that.
Lower units will interchange, I think there is a small difference in gear ratio or propellers, but can’t say for sure. I used to know that but I disremembered it temporarily. I do know that my Dad took a lower unit off a 4423 and put it on his 4425 and never noticed any difference.
Hope this helps.
Best,
PM T2
He's livin' in his own private Idaho..... I hope to go out quietly in my sleep, like my grand-dad did..... and not screaming, like the passengers in his car...
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