Won't start Poulan yard tractor won't turn over. I can start by jumping directly to starter.

could be a safety switch or a ground problem check the ground for corrosion and make sure it is tight at all places then check each safety switch they usually have one for the seat,mower deck and clutch/brake pedal

Have you checked the battery terminal connections? Is the battery charged fully? Are you sitting on the seat when you try to crank the mower? Could be any of the above but most likely battery connection or the battery is discharged or old.

Click means solenoid has enough battery power but maybe not enough battery power for the armature of the starter to spin, it may be low battery or bad solenoid contact - inside it, (copper washer and pin), or thirdly it may be the engine is stuck so try to turn it a bit by hand to rule this out. Turning the engine a bit by hand may also free a starter gear that has jammed on the flywheel teeth.

there is a plastic connector that holds the steering shaft down into the drive gear the plastic cracks and wears out then the gear jumps passed the teeth its about a $15 part

check the safety switch on the brake/clutch pedal bypass it with a paper clip to test it

with jumper cables jump from the battery direct to the starter if ok sounds like the safety switch on the brake pedal is bad

try and jump start it direct to the starter if the cables are weak they will get hot and it the starter is bad they will as well this will isolate the cause

when changing the belt you might have knocked off a wire to a safety switch

Is the engine free to rotate? Can you move it by hand? If not, the starter can't.
If so, try removing the plug and starting it.
Gary

Sounds to me like the battery hasn't enough charge to turn the engine. Taking the starter off and testing it doesn't require much power as it doesn't have to turn the engine. Check the battery and also that the charging system is charging the battery back up. Alex.