putting a weed eater engine on a bicycle?

Chainsaw motors have more power..A typical weedwhacker motor is so puny it has difficulty propelling a bicycle with an adult on it..theywork OK for kids ona skate board though!..

I see a guy locally who put a 3.5HP Briggs on a 10 speed bike,he put the engine over the pedals and used a centifical clutch like a go-kart used,with a #35 chain sprocket welded to the original ones on the pedals..I see him go flying by my house often going at least 35 mph!..

He says the cops here pull him over a lot ,because your not supposed to have a "moped" with more than 1.5 HP,anything more,its considered a motorcylce,and needs to have all the usual things required to be road legal,and have motorcycle plates and insuranace on it..(and they want us to be "green" huh?..)..as far as they are concerned he's no different than the kids who ride mini-bikes and ATV's on the streets illegally..

I think that sucks,because I have been tempted to put some of my small horizontal shaft engines on a bike or make a 3 wheeler..be nice for trotting to the store 1/4 mile away,etc..I have a 2 stroke Tecumseh A600 off a snowblower that would be ideal,4 hp and it loves to wind out!--plus its dinky and easy to mount in tight places..

I see a LOT of o;d bokes at yard ales,and even at the landfill!--but most of them are GIRLS bkes,and though they would be easier to put a fas engine on (no upper bar to be in the way),I wouldn't be caught dead riding one..they look weaker too,probably flex and fold in half while going down the road!..I see lots of small kids bikes with 12" wheels too,so far I haven't come across a suitable men's 10 speed..I'd love to score a "Sting-ray" 20" bike with the 3 speed rear hub and a coaster brake,that would be really cool,but those bring big bucks now,doubt I'd ee one being offered free anywhere..

My brother in law has a three wheeld 3 speed bike rusting in his backyard for 5 years at least,that wouyld be an ideal gas conversion candidate--but he refuses to part with it,despite being offered what I considered good money for it..(its sitting next to his roto-tiller,that I put a like new 5 HP Briggs on I had,and he busted the rope on the starter and never used it ONCE!--there it sits outside for 4 years...probably scrap now..

I'm not sure if a ten speed would shift with a gas engine powering it,the chain might come off if the engine is keeping torque on it..a 3 speed one with the gears in the hub would probably work ok though..be neat to hear it going through the gears,like a motorcycle..