I own a John Deere JS20 self-propelled mower. I was mowing my backyard and hit my barbecue grill with the front of the mower. The mower speed (rpm's) dropped dramatically. I checked to see if the throttle bent or if the sparkplug wire in the front was damaged. I discovered that the throttle linkage is on the side, and I did not see anything loose or damaged. If I move the lever on the mower handle to increase the mower's ground speed (which also increases the engine speed), the mower does not speed up much at all. Do you have any clues as to what I should check?

Could it be a clutch problem? Or are you missing a drive belt?

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.

First guess is the flap that protects you from flying debris and grass. It must pass vertical and then be dragged under the mower when going from forward to reverse.

Mower blade might be bent, that would cause it to run out of balance and it would slow down the speed of the engine.

John Deere Model JS38 Walk Behind Mower Parts


About half way down the page, left hand side. About $20.

Semper Fi,
Z

Check under the cover of the self propel unit to see if the belt is off the bearing or broken.

Take big screwdriver and stretch on the rim.

Have the valves adjusted for they are required to be adjusted every year refering by the owners manual. If the lash or gap is too big this will cause the symptoms your having. Also replacing the spark splug and changing the oil is recomended every year too

Make sure that your gauge wheels are not running on the ground during mowing,they should only hit the ground when you engage a high spot on one side.also when you level the deck the front should be a 1/2" lower than the rear.