My 48" scag walk behind will stall out if the (deadman) handles are not held down

if not a simple cable adjustment
or drive shaft isn't broken between gearbox and wheel

will have to inspect the internals of the gearbox
this is close to the walk behind gearbox
How to take apart and reassemble Peerless 700

Your mower doesn't have enough power to handle very thick grass at high speed. You need to go slower across the lawn. That's easy to do if this is a push mower (just don't walk so fast) or if it's a self-propelled model with a speed control. But if it's a single-speed model you'll have to mow the lawn in fits and starts: squeeze the lever to move it forward; release it when you hear it bogging down; wait for the motor to reach full speed; squeeze the lever to move it forward again; repeat. Also, is the grass very high? If so, try setting the cutting height higher on the first pass, then lower it for a second pass. Finally, make sure the blade is sharp.

The clutch probably needs adjusting

if its hydro drive check the linkage adjustment if its belt drive they never worked very well you need to push down on the handles to help it tighten the belt

you can adjust the handle not the switch try and swapping the switch with the other side and see if the problem follows the switch

Down behind the back wheels should be knobs on each side for folding. The handle will fold down on either side of the mower on top of the deck. var geo_Partner = '1890d1e7-e721-4f9c-b474-1a19eda23e94'; var geo_isCG = true;

look and see if the Kill wire is hooked in wrong spot on linkage therefore grounding it out when you squeeze handle

The dead man cable or "deadman bar".
It kills the power to the magneto and stalls/shuts down the engine.

the springs that control carby is there leaves or grass stopping it from moving ,some lawn mowers have bad desinge for air flow off ****

is the deadmans handle pulling the cable enough to cancel the off switch? if not relase the cable from the handle, TIE A KNOT IN IT(!), re fit to handle, & bingo!
If the cable is working well enough already DONT tie a knot, it wont help, its the ignition coil! ( around £30)