Buy the Predator from Harbor Freight. I have been real happy with that engine and they have them on sale all the time. I bought one for my Yerf Dog kart and have clocked it at 32 mph. You will not hit 50mph with this engine but they can be modified by removing the governor system for direct throttle control. Parts and kits are available for this. Google it. You may get close to that speed with the right sprockets and changing the governor and air vane.

For that kind of speed, you're gonna want a small motorcycle engine. Rigging the clutch and shifter relatively easy, hardest part is fabricating an exhaust that works but doesn't stick way out. Think old VW.

Best bet I reckon would be a 2 stroke Rotax engine as long as you don't mind spending 300-500 USD. I wouldn't go with any Chinese copy, parts are hard to come by and you'll be needing a lot of them....The Rotax from the Aprilia RS125 will give you a solid 35hp which in a kart will be like strapping a saturn 5 rocket to a car...very fun

use a lawnmower engine

I'm currently building a go kart and I was now stuck on one the most important element in it. What engine should I put on it? I already have an idea but I'm stuck between two models, or brands if we can say.

I'm seeking reliability and fuel consumption, yet I want power and speed. I weigh 145lb and I want to achieve about 50mph +. What, between those three, can be my best choice:

- Predator 212cc 7hp engine or any honda clone engines

- Lifan/Piranha 140cc pit bike engine

- Dirt bike engine (yet I don't think my wallet is thick enough to afford one, yet)

Thank you all!