Get someone to help roll it until you find the tightest spot - can make a difference. Manual says 10lbs pressure should move belt by 11mm (7/16") from relaxed position using the belt tension gauge.
If you don't have the tension meter, as a sanity-check you can grab the belt with a couple fingers, it should have over half-inch from pushing down to lifting up.
10 lbs isn't much pressure.
If up/down is under an inch when I change oil, I don't bother checking with the meter (slacker).
Tight is worse than loose, IMO. Tight can give squeaks/creaks, a low frequency hum, and wear out bearings and sprockets quicker.
Compression should be 180 +20. Meaning 200 is fine, but under 180 is bad. If that's the source of vibration, you'd have significant disparity between the cylinders.
A fuel issue with one or the other cylinder can cause similar issue to a low compression cylinder. Tougher to see, but same basic symptom - one cylinder not firing well. Doesn't hurt to throw an ounce per gallon of seafoam in the gas. That does a better job cleaning up fuel resins than any injector cleaner I've used, even though it sounds a little redneck.
Another way to tell if a cylinder isn't firing well is to use a laser thermometer & check the temp of the headpipes. If one is significantly lower than the other (use high-idle choke lever to spin it up a little) then ignition, fuel, or compression is bad in the low cylinder. Prob the quickest way to isolate to engine?
I did put new plugs in it and change the oil when I got it home. I will check the compression and see if the cylinders are close to each other but thats about all the harbor freight kit is good for.
as for the belt, should it feel somewhat tight? just want to make sure my belt adjustment was done properly because it is drastically tighter than it was initially on the bike when I bought it. it had a ton of play initially.
XC, KP, & Custom MuscleVic in Boise