Honda produced a 50 cc minibike, the Z100, in 1961 for use in the Honda Tama Tech amusement park. Riders reportedly appeared simian while on the Z100 and the minibike was nicknamed the Honda Monkey. Honda modified the original Z100 for street use and dubbed it the CZ100 in 1963. The Monkey underwent further modifications for 1967 and Honda released it as the Z50M. For 1969, the bike underwent further improvements and released as the Z50A Mini-Trail in the U.S. and the Monkey in the rest of the world. In 1970, Honda released an off-road version for the U.S. market dubbed the QA50.
Honda marketed the QA50 series as a youth model minibike. It featured patented Swivel-Lok handlebars that folded down so the bike would fit in the trunk of the family car. Honda dubbed the debut model of the QA50 series the K0. It was available from 1970 through 1972. The QA50 K0 had an OHV, single cylinder, 49 cc engine with an automatic clutch and two-speed transmission. The K0 was available in three colors, Gypsy Yellow, Sprout Green and Scarlet Red.
For model years 1973 through 1974, Honda re-dubbed each year's QA50 as the K1, K2 and K3. The only differences between model years were the colors offered. In 1973, the QA50 K1 was available in Hawaiian Blue Metallic and Candy Ruby Red. The 1974 QA50 K2 came in one color, Candy Orange. The final year for the QA50, 1975, saw the K3 in Mars Orange.
Engine - Air cooled 4 stroke OHV (pushrod) engine, single cylinder angled 80 degrees from vertical, displacing 2.99cu-in or 49cc.
Oil - Wet sump, takes SAE 10W40 (2.1 pints or 1 litre).
Tappet Clearance - 0.0002in or 0.05mm.
Sparkplug - NGK C7HSA with 0.024in or 0.6mm gap.
Points - 0.012in or 0.3mm gap.
Transmission - 2 Speed with wet semi-auto multi plate clutch.
Final Drive Chain - 428 x 120 L.
Cylinder - Type = Cast iron, Ovality limit 0.002in or 0.05mm, Taper limit 0.002in or 0.05mm, Cylinder to piston clearance 0.001in or 0.02mm limit is 0.004in or 0.11mm.
Piston Rings - Gap = Top & 2nd 0.001 - 0.014in or 0.15 - 0.35mm, Oil Ring = 0.008 - 0.02in or 0.2 - 0.5mm.
Torque Wrench Settings for head and barrel studs - 10.1 lbt