Could be the 40 amp breaker. Make sure those connections are tight as well as the ground from the battery to the bike.
Dropping to 9 volts is too much.
I will point out that bad grounds or connections do not and can not cause this kind of voltage drop. That said a poor ground can impede a proper charge.
But we aren’t looking for parasitic draw, we are looking for enough draw to pull a battery down in a hour or two. That aside it is true that most basic multimeters can measure amp draw up to ten amps by putting in series. At that point what would be the point of checking voltage if you were only interested in parasitic draw. It would be more helpful if I said for someone without a multimeter that a basic circuit tester, a lightbulb type put between the negative cable and the negative side of the battery would light up if serious draw was involved.
A reasonable assumption as we are not entirely sure why his bike is hard starting except for the drop to 9 volts with starter engaged.
if he bought a cheap battery, very possible the meter is the same, might be a analog meter or off calibration. Would a drop to 10 volts be acceptable? possible it does drop to 10 but meter says 9.
A drop to ten volts is still too much for a draw from a starter with the proper battery and proper charge. When voltage drops that much either the battery has weak cell(s), starter windings are shorting to each other, a large draw from a different area in the starter circuit when the starter is engaged.
