This is short shaft version from a lightly used weed wacker. All mods done at home, no extra purchased parts. Stock ignition.

All tests with an 18x6 Dynathrust prop, unleaded regular gas, and Stihl oil at 32:1.

Stock engine except for cut down flywheel fins............ 5800 RPM. 8.8 lbs thrust.

Stock muffler, gutted, bigger outlet tube..................... 6200 RPM, 10.1 lbs thrust

Above muffler, plus larger carb from old chain saw ..... 6600 RPM, 12 lbs thrust.

Above muffler, carb, blocked decompression slots ...... 7000 RPM, 14 lbs thrust.

Not amazing numbers, but very inexpensive to buy and operate.