I have always had great power from novarossi engines and the durability is second to none.
I don't trust the O.S. line of motors because their quality control isn't the greatest. One engine could last you 1 gallon and the next could last you 13. So I wouldn't want to spend about $500 for the speed version and have it blow in a gallon
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Novarossi engines are great on quality control, power and fuel economy.