dual chain drive whipper snipper bike

hey all,
I plan to build a chain driven whipper snipper bike and could use some help.
I have a few 25 and 30cc whipper snipper engines.
I was thinking of having a small sprocket on the engine and a large sprocket on the left side of the rear wheel which would give me around a 4:1 ratio. I know this wouldn't be enough so i was going to use the pedals and the normal bicycle setup as well(my motor would be able to run without it turning the pedals) I'm just not sure if the whole setup will be practical?
would the engine engage at a manageable speed and what would stop speed be? (centrifugal clutch)
if this system is impractical i would ditch the pedals and give the bike a big ratio still using 2 chains

thanks for the help.
I've been thinking about it more and i'm coming up with new ideas.
So i was thinking about 3 chains, i want to have the pedals so the usual bike setup with pedals would be one chain, then i'd use a jackshaft and 2 chains to get a big ratio somewhere between 15 to 1 and 20 to 1. But my new problem is that if i'm looking along the shaft of my motor towards the engine, the engine is turning anticlockwise (i hope ppl can understand me)
The pedals and normal bike stuff is all on the right side of the bike so i'd end up welding another sprocket on the left side of the bike.
So if i hooked it all up so that the bike is travelling forward my engine will be hanging off to the right side of the bike, which i don't want.

To combat this problem i could switch all the standard bike pedaling mechanisms and freewheeling section from the right side to the left side of the bike, problem then is if the engine is running through a sprocket i would weld on the right side of the wheel it would end up turning everything connected to the wheel including the pedals which i definitely don't want, so to combat that i'm going to need help
the question is can i reverse the free wheeling section on a standard back wheel to freewheel the opposite way for when the wheel is going the other way round?

bloody **** thats hard 2 explain and to me seems hard to interpret but good luck help givers