What's better for making a moped go?
A 2-cycle engine or a 4-cycle engine?
A 2-cycle engine certainly has it's advantages over 4 strokers, but then again a 4-cycle engine isn't without it's merits.
A 2-cycle engine has no valves or camshaft and has fewer moving parts (and fewer parts overall) which makes it much lighter than the comparative 4-cycle engine.
But a 4-cycle engine can deliver more low end torque (not always but can) than a 2-cycle engine. And because a 4-cycle engine when running properly does not burn it's oil supply runs cleaner than a 2-cycle engine.
Now lets look at fuel economy and power.
Every down stroke on a 2-cycle engine is a power stroke so you have combustion ever revolution of the crankshaft. Now in a 4-cycle engine every other down stroke is a power stroke- so you have combustion every other revolution.
Now you'd think that because a 2-cycle engine fires twice as often as a 4-cycle engine it would make twice as much power, but if thats what your thinking you're wrong. Why? because 2-cycle engines rely on the pressure of the incoming charge of gas and air to push out the exhaust. This leaves exhaust gas in the cylinder with the fresh charge and means there is less to burn so less power is made per power stroke than on the 4-cycle engine which dedicates an entire stroke just to pushing out exhaust gases, and there-for less burned gas remains in the cylinder when fresh gas comes in and is burned.
There is a way however for a 2-cycle engine to make far more power by the more complete exhalation of exhaust gasses. This requires different port timing so that more exhaust gas can exit while more fresh gas can enter the cylinder. This would mean having a taller exhaust port so exhaust gasses can begin leaving the cylinder earlier and a intake port that is extended further down the cylinder wall to allow more time for the fresh charge of gas from the crankcase to come in. But now there is a new problem- unburnt gas and oil is lost with the exhaust gas in the effort to better scavenge exhaust from the cylinder creating a powerful engine that runs very dirty and wastes gas. I'm going to guess that engineers of small 2-cycle engine are going for economy rather than power most of the time.
And the final point: weight power and gas mileage.
A 2-cycle engine is lighter than a 4-cycle engine and can produce marginally higher horse power for it size- it there for uses less power (and gas) to haul it's own weight and more to haul yours. A 4-cycle engine offers cleaner burning and can deliver better gas mileage but is heavier so if you spend time actually pedalling your moped it gives you a little extra exercise- and it also has to use more of it's power hauling it's own weight as well.
There is no conlusion this writing, it is inconclusive- maybe you have an opinion over what the better type is.
= this can't be the proper spelling, or is it?
And if you really must have a source
Here is one :General Power Mechanics- 1968 Mc Graw hill