Yes, you read correctly, a Hemi Big Block scooter (ala “moped” / “mini-bike” / “looks like a Vespa”).
Fact of the matter is, the Honda 139QMB GY6 engines used in just about every Taiwanese / Japanese / Chinese knockoff scooter now-a-days are actually fitted with hemispherical combustion chambered heads. So, technically speaking, they’re Hemi’s.
Ya… didn’t think you’d buy that. Regardless of the shape of the chamber, nobody’s going to confuse a 50cc (er, 49.5cc) scooter motor with a venerable Hemi (of any generation of build).
That said, you can get a lot more than 3 horse (as they’re equipped typically stock) out of one of these motors with about 700 USD worth of upgrades.
What you’ll need..
– 23 to 25mm carburetor along with a carb “spacer” (it’s actually an adapter – think “square bore to spread bore”, but not obviously, just the same purpose – the larger carbs are for the 150cc motors, and won’t fit without the “spacer”.
– larger intake (its a pipe elbow but is actually serving the same function as an intake manifold on an automobile – it sits between the carb and the engine).
– rip off the stock air-box setup and slap on a simple free flow filter element. Most of the aftermarket valve cover breathers for a small block Chevy / Ford / Chrysler will be right about the right size. If not, a small motorcycle air-filter band-clamp element will work nicely.
– unregulated ignition box. These engines use a CDI (capacitive discharge ignition – think “an MSD box for a scooter”) which works nicely, however all of the OEM / stock ones have built in rev limiters to limit speed and power output. Gut it, install a new unregulated one, and add a performance ignition coil (typically these come with the ignition cable).
– performance grade camshaft with steeper lift and longer duration.
– 52 mm big-bore cylinder kit. This kit will typically include a 50cc stock “jug” (cylinder) bored out to 52mm, along with a decked (milled) 50cc head that’s been ported / polished and has larger intake and exhaust valves. Of course the piston itself, rings, wrist pin, and c-clips should also be included. You’ll reuse your original crank case, timing chain, crank-shaft, and such.
– the shop manual. Dig up a 139qmb 50cc manual written in English. Good luck on that, and let me know when you find one.
We’ll take some pictures at tear down, and do something up for this. It’s a project – no hurry on it, so don’t get your hopes up for it to be done too quickly.
… and we’re probably going to end up needing a lot more parts…