Fun and practical

[Gibsonvair]

I've recently completed a new project. It gets apx. 60-80 mpg. I will verify things later. It is a 20" motorized bicycle. Top speed on a flat is 30 mph exactly. Downhill it has topped out at 38mph. It rides 2-up and weighs 62 lbs. without the luggage baskets. It is very off-road capable and can climb steep hills. The limitation is traction in mud and dirt.
OK, it's not really completed. I've just removed the engine to modify the mounts after finding cracks. All in all, we've rode over 100 miles and burned almost 2 gallons of gas/oil mix. I used it all week to do chores and go fishing.
Steve Gibson

[DonR]

Specifics?

[Gibsonvair]

I kinda put that message out as a teaser to see if anyone might be interested. This is mostly an automotive forum, but it does get good gas mileage.
It is an early 90's Huffy brand BMX style bike. The engine is from a Hoffco brush-cutter. The engine is an 85cc two-stroke, 3.5 hp @4600 rpm,Tecumseh with points/magneto ignition and the pumper style carb mounted on the opposite side of the crankcase and in-line with the cylinder bore centerline. This makes it fit in the small frame opening fairly easily. A cut-off 3/4'" shaft from a 5hp Briggs and Stratton with a 3/4-10 nut welded to it is utilized so it can thread onto the Tecumseh crankshaft. This in turn allowed the use of a standard Comet torque-converter. The crank set and bearings were removed from the bottom bracket and replaced with a "sealed bearing" kit with an inside diameter of 19mm. A 3/4'" keyed shaft couples the driven pulley of the torque converter on the left side of the bike (acting as a jack-shaft) to the right side of the bike where a #41, 10 tooth sprocket is attached. A #41 chain drives the freewheel on the rear wheel. A 48 tooth sprocket was welded to the back side of the original 14? tooth freewheel sprocket. It could also be bolted due to the bolt pattern in the sprocket used. The gear reduction on the torque converter is infinately vairiable from apx. 3:1 to 1:1, maybe a slight overdrive. It works really well and is rugged and simple and coasts like a normal bicycle. I have taken jaunts of 30 miles on one 48 ounce tank.
The engine is solid mounted to the frame with 1/8 " plate welded to the thin wall tubing. Pictures are worth a thousand words so I'll post a link later.
Steve Gibson

[beatr911]

Sounds like a fun project.
Looking forward to the pictures.

[The Atomic Ass]

Interesting, but not earth-shattering. Have a gander at my recent tanks on the 'mule.

And I drive faster than 30mph most of the time.

[Gibsonvair]

Building this bike made me think of what kinds of effortless speed and economy could be obtained with an aerodynamically effecient fairing. I think that is what is keeping the fuel effeciency and top speed down. The belt drive does probably rob some power, but makes it simple. To see pictures, I have an album of photos I took last night and today: Picasa Web Albums - Steven - moto-bike

[Gibsonvair]

By the way, the tank is only 32oz, not 48oz. My wife and I ran out of gas on a 22mile ride. We made it 19.95 miles. I am using a bicycle "computer" and am in the process of verifying accuracy. That 30 mile trip must have been a fancy of my imagination! How is it though, that a Kawasaki Ninja or a 400cc mule gets better fuel economy?
Steve Gibson

[Frank Lee]

Worst problem is likely the 2 stroker itself. Those old carb'd ones usually aren't that efficient- lotsa raw gas out the exhaust, rich mixtures, etc. Then there is gearing.

I have a nice strong Stihl chainsaw engine I'd long wanted to put on a bike but never got around to it, partly due to laziness and partly due to realizing what I really wanted was a little 4 stroker like a Honda 50 or something.

[Christ]

I have a 196cc generator motor that's 4 stroke... but it's too big to be legal w/o a M-class license in PA.

1.5HP max rating in PA, as well, and less than 50 cc, w/ a designed top speed of less than 25mph.

PA's laws are based on optimistic human-max figures, I presume.

[younggun]

brakes?