Guess it's a matter of personal opinion. For use in average suburban traffic (or anything above 25-30mph sustained), no argument, totally underpowered. For trails, quite adequate. Still, 35mph is no problem for my stock K1, even with a combined 300lbs of rider & tolerant wife on board. Freshly rebuilt stockers can usually spin the rear tire on gravel from a low roll...not bad for 72cc. It's not a surplus of power, just crisp throttle response and an ultra-low first gear. It works well offroad.
I wouldn't stretch oil change intervals to the 1K mile range. An extra $25 per year, for a few more oil changes, is damn cheap insurance. No need to use expensive oil, just bike oil formulated for use with wet clutches. I am dead serious about keeping clean oil in these motors. The oil "filter" is only a small chamber inside the clutch face, just behind the throwout bearing flange. It's surprisingly effective...when properly maintained. That said, it only holds maybe a couple ounces of clutch debris then abrasives begin circulating through the motor...making short work of the cylinder walls. Nearly every engine I've rebuilt has had the oil spinner filled with hard-packed dirt. Check out the attached pix and judge for yourself.
It really doesn't take a whole lot of time, effort or money to keep one of these bikes running like new for many years & miles. IMHO, stretching oil changes & ignoring the filter is penny-wise and dollar foolish...no disrespect meant.
As for making one of these bikes roadworthy, for an adult rider, anything but freeway use is possible and has been done. That, however, is a long discussion and off the original topic.
