Another reason why the engine is still running lumpily is the cylinder keeps going out of alignment. On an S50 there are 3 screws/bolts holding the cylinder to the bed casting underneath and on Andy’s S50 only 1 bolt is present, hence why the cylinder is slightly oscillating and needs readjusting. Andy doesn’t intent to run this engine a lot and wants to have it as a mainly static ornament so it’s not a big issue in this case.

Made Andy’s day.

8ve had the same problem but on a traftion engine, alchins are always wheezy. Thats a nice looking engine and thanks to you, a functional one. If itbwere me i would have taken the studs out and cleaner up that face .

The location of the valve is also wrong, it would help to screw the valve rod to move the valve towards the left, so that its more in the middle. One port opens way more than the other, and the valve is probably closing the exhaust port as it does so.