""I was riding the bike over the holidays in Satellite Beach, FL and Tried to pay more attention to the feel of the bike. It seems jerk the bike right, with loaded
throttle acceleration.""
This "jerk to the right" would possibly be the loose swing arm bolt.
"sounds like a fleet of shopping carts rattling"
From the video it sounds like the cable bracket vibrating on the front fender.
These are two separate issues. The engine itself sounds solid.
I mostly agree with this. The motor sounds okay to me, too. However, torque steer (if that's what happening) means excessive lateral deflection of the swingarm & wheel assembly. With 88cc, there's just not much more torque than a stocker; it really takes a 55mm+ stroke to make enough torque to start flexing the pivot bushings and that means 130cc, minimum. The pivot bolt would have to be really loose...so much so that it'd be impossible to miss...to be the root cause. OTOH, the swingarm is a structural component of the rolling chassis. Without a solid pivot assembly: bushings, internal spacer + bolt, properly torqued, the lower engine mount & swingarm mount would be an incredibly weak point for the frame. He says he replaced the swingarm bushings and that, imo, requires a level of mechanical skills that, ostensibly, rules out a rookie mistake like leaving the swingarm pivot bolt loose. I'm left with the impression that it's something basic...but arcane enough to be overlooked.
Having a number of other bikes to use for reference should make this easier. Quickest test, at this time, swingarm deflection. Grab the chain with one hand and squeeze it like grip strengthener...then repeat the test with one of the other bike and note any differences. If there's significantly more lateral swingarm deflection, you'll see it; then it'll come down to figuring out why. If not, time to look elsewhere, which is why I suggest the engine & frame swaps. Gotta figure out what/where the problem is: engine, chassis, owner perception...or some unusual combination.
As much as I don't expect this to be an engine problem, it's not completely out of the question...yet. Every once in a great while, one's luck can be spectacularly sour. Build enough engines and eventually you'll come across one that insists on running through the hall with scissors. A crank that's off by an extra couple of thousandths, a tweaked flywheel, or even an imbalanced clutch, is all it'd take and none of those are common enough to suspect, or all that easy to check. I don't know how one would check clutch balance, other than by swapping them & retesting. I've not run across clutch balance problem, ever (yet?) thus it seems highly unlikely, imho. That said, we're making blind guesses and it sounds like Darrel has thrown "
everything but the kitchen sink" at this motor, yet the answer remains elusive, the vibration unchanged. Until the problem can be isolated (frame, engine, swingarm, owner perception) I wouldn't go back into the engine. At most, for now, I'd try a flywheel swap...which I thought had already be done. IMO, the problem has to be isolated and the list of things to check is getting short.
