I've got an ASP 52 four stroke, super little engine in a Seagull Spacewalker. Starts and runs well. I did have a problem with the exhaust port working loose and losing compression and power but a replacement from Just Engines cured the problem...on closer inspection of the new head it has been modified and redesigned so as to stop the port leakage........nice touch from ASP to improve the product and cure a fault.