My first motorcycle - or first transportation of any kind at 15 was an ’82 Kawasaki AR80. My dad chipped in on half the cost and my job bagging groceries covered the balance, saving me from the torture of riding the school bus as a sophomore in high school. Probably not legal on my learner’s permit, it existed in a quasi-legal world where “brake horse power” was limited to 5 and the police hazily interpreted this as 50cc maximum displacement. I decided to push my luck because my only other option was a Honda MB5 and I thought they looked dorky. Only once did a cop hassle me about the size of my bike but no ticket was written. At least not for that. Many other infractions, yes, but not displacement.
I rode the wheels off that bike for a year and had a great time but upgraded to a Triumph Spitfire. I never looked back and for years thought it was a bit lame that I got so excited about riding a moped on steroids. But perceptions change, I’ve mellowed and I like seeing vintage two strokes on the street. So I began my search for another AR80 to see if that excitement I’d felt 32 years prior was still there. After a few months of searching eBay and Craigslist, and nearly buying an overpriced AR in NYC for $2500, I lucked upon one in Wisconsin for $500 + shipping. The owner stated he thought it needed proper jetting, but said it ran. Two weeks later it was offloaded into my garage. Little did I know the purchase price would be the cheapest thing about this bike and that getting it running properly would be a war with many lost battles. My pal Scott Lelievre was properly chuffed at this purchase and proposed that we resto-mod it. His proposal came after the bike refused to respond to different jets and sucked most of its crankcase oil through a failed crank seal. On a 2-stroke this means straight into the cylinder where it became an enormous plume of blue smoke on the first few runs on Micah’s dynamometer at AF1 Racing in San Marcos. If Scott wanted to rebuild my sick bike into a world dominator (cough-cough) who was I to disappoint him?
Any state fair would be incomplete without the World’s Tallest Midget - and that’s what we set out to build with this tweaked and massaged ’82 Kawasaki AR80. According to www.motorbikesp... my bike originally made 10.2 hp (5.34 ft-lbs torque) at 8500 rpm - a figure unlikely to elicit much enthusiasm, but a good starting point nevertheless.
As I plan to write a blog on the build, I’ll keep it short. We started with an Autisa 98cc big bore kit from eBay but it was badly scored (buyer beware). We then sourced a big-bore kit from www.1977mopeds.com which was a “Char-Mo" Chinese made piece of shite, not bored circular and seized immediately on the AF1 dyno at half throttle on two sides despite precautions. So we bored the Autisa, sourced a +1 piston from England and used that. The stator/flywheel was not properly torqued and rotated slightly throwing the timing off causing detonation which lunched the piston. Now it sports a YZ125 piston with custom bushings to fit the AR80 crank pin. Other mods are:
Custom exhaust from Andy Cline in Houston (formerly of Jemco)
Moto Tassinari V-Force Reeds (V364A)
Polini PWK 24mm carburetor from the awesome www.Treatland.tv
Sava Tires MC7 3" rear and 2.75" front from the awesome www.Treatland.tv
Lambda Oxygen Sensor Stage6 S6 EGT digital from sip-scootershop.com
Our dyno run today at George’s shop Precision Power produced a peak horsepower of 11.6 (5.67 ft-lbs torque) which arrives at 10.5k rpm. Scott noted that the original stock 10.2hp figure from Kawasaki was very probably measured at the flywheel not the wheel, so subtract around 15% for drive train loss = 8.6hp wheel hp: a more realistic number. In that context 8.6 to 11.6hp is more like +35% gain. Considering it’s nearly a 100cc bike now, that seems reasonable. The down side is that it's peaky. As in really, really peaky. At 8000 rpm it's making a paltry 5hp. To get into the power band requires the kind of flogging that only happens when one is trying to grenade their engine.
Still on the to-do list is returning the bike to Andy in Houston to weld an adapter onto his custom pipe permitting a more effective silencer: it’s absurdly loud with the tiny silencer he specced. Also I’d like to remove the piston and ship it off to be teflon coated which I’ve heard is effective for calming piston slap.
I don’t have the full dollar figure of the upgrades, but at least the dyno time was reasonable. If nothing else I learned a lot about 2 strokes and ate bbq with my pal Scott.