Motorcycle Repair: 1978 Honda Trail 90, honda trail 90, resistance one

Question
I'm trying to diagnose why my ct90 doesn't seem to be charging the battery.  The new battery alone registered about 6.4 v DC not connected to the bike.  It was the same connected with the ignition off.  With ignition on it dropped to 6.3ish

could this identify a short or is power being consumed?

While the bike was running from the alternator before the rectifier we saw anywhere from 5-40 v AC (depending on throttle).
After the rectifier we got about 6.4 to 6.5 v DC. (depending on throttle).
At the battery we got 6.3 to 6.4 v DC (depending on throttle).

Is my alternator producing enough?
Is my rectifier working properly?
Should I just replace all my wiring?

Answer
Canaan, the drop in voltage when you turn the ignition on is normal. There's three parts to the charging circuit.  The stator under the flywheel, the rectifier and the voltage regulator.   That system only puts out about 2 amps and the battery doesn't charge at idle so the engine has to be reved up to about 3000 rpm before it starts to charge.  Check the battery voltage when the bike is reved up.  It should be about 7.5 volts or there abouts.  If the voltage doesn't increase when the engine is reved up, check the stator for continuity.  There should be three yellow wires.  Make sure they all have about the same resistance between the three coils and none of them have continuity to ground.  Next check the recitifier and make sure the diodes are working correctly.  They should have high resistance one way and low resistance if you reverse the leads.  If those check out fine, it probably the voltage regulator.

Good Luck
Rich