Can I control speed of self propelled mower ?

The cable may be stretched and should be replaced.

disconnect the spark plug turn the mower on its side and inspect the drive belt on the pulley above the blade (on the crankshaft) it may have a shroud over it. Also there is a small gear case that maybe dry that the belt drives, that goes to the wheels, Also try lifting the drive wheels up off the ground and engage them and see if it still does it. if it stops once lifted it might be the bushings on the axle its self.

i would guess that the belt is'nt tight enough when engaged. when you press the drive bar on the handle it should make the belt really tight if not it will need replaced. sometimes the gears in the wheels will mess up. there are videos on you tube that describe that and also the belt.

Some self-propelled mowers include a speed control, but sometimes it may seem that no matter how you adjust it, the mower just creeps along at a snail's pace. Most likely this isn't a mechanical malfunction, but an adjustment is probably needed.

Very tall or thick grass can bog down a self-propelled mower, but adjusting the height of the blade may allow it to roll through and cut the grass at normal speeds. If the blade is low, the amount of cutting required may slow down the movement of the entire mower. The frame of the mower may also stick in the high grass. Raise the blade little by little until the mower rolls at the appropriate speed. Going up hills may cause a similar response.

It's possible the drive belt on the mower can slip. Inspect this part to see if it is loose or cracked, and replace the belt to restore power.

I believe that engine speed will adjust travel speed. GOOD LUCK.

use 10W-30 or for best performance, use synthetic 5W-30

Cable could be stretched belt could be worn or old, if it has a gear box maybe it slipped a gear or lost some teeth. Do some investigation, Good Luck

no adjustment for drive

Verbally threaten to trade it in for a riding mower.

Your self-propel is probably belt driven. Belts can make an awfully lot of noise when unhappy. Possible it has rolled over and is running on the wrong side of the belt or is worn and just needs replaced. Hope this helps.,