My Toro mower is 7 yrs old. 3 speeds, blade

These push-mowers have a limited power, when you hit tall grass there is much more resistance on the blades. Even higher power riding mowers can stall on tall grass.

If speed varies depending on how much grass you are cutting, look for loose or badly worn belt. If constant slow speed when engine is running at full noise can only be a slipping on pulley or clutch. Most likely clutch. Normally slipping generates much heat so look to your clutch or pulleys. If drive key has separated there will be damage to shaft with metal dust showing.

There is not a governor on newer mowers. Ease mower thru grass slowly, if starts to slow down stop, let mower speed up. In tall grass only use 1/2 of the deck width with side discharge open. Ensure spark plug is clean and gapped properly, replace once a year. Ensure air filter is clean, replace once a year. Ensure oil is full. 30w oil. Always use Stabile in gas. Use carb cleaner and clean outside of carb to ensure choke lever is free to rotate.

Not enough torque. Only use 1/2 width of deck on tall grass, go real slow, Ensure side discharge is open! Ensure blade is sharp. Replace spark plug once a year and clean replace air filter. check oil level 30woil.

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.

Yes, it sounds like you need to adjust the blade brake clutch (BBC). I have a PDF service manual that explains it. If you post your email address I can upload it to you. Here's an excerpt from the manual:

BBC
BBC Adjusting the Blade Brake
1. Stop the engine. Pull the wire off the spark plug.
2. Remove the two screws securing the screen
panel to the top of the mower housing as shown
in Figure 22. Remove the panel. (The panel they're
referring to is the red screen between the motor
and handle.)
3. Move the control bar down and lift up against the
handle. With the control bar against the handle,
measure the spring length (L) at the front of the
spring as shown in Figure 26.
4. If the spring dimension is greater than 32 mm
(1-1/4") an adjustment is needed.
5. To adjust, loosen the bottom jam nut on the blade
brake cable as shown in Figure 27. Adjust the top
jam nut until spring dimension is as near as
possible to nut; not less than 25 mm (1") See
note below.
NOTE: Adjusting the top jam nut too high can
cause the cable end to crush the plastic fitting
when the control bar is moved up against the
handle. If the spring cannot be adjusted to less
than 32 mm (1-1/4") before the cable end
contacts the plastic fitting, the clutch belt is worn
out and should be replaced. After replacing the
belt, adjust the cable per the above procedure.
NOTE: 1990 and newer models are equipped
with finger tip adjusters that do not require tools.
Use the same adjustment criteria on these
cables.

Hello,

The reason the blade slows down when the grass gets thick is simply because the mechanism operating the blade is weak and cannot move fast when on thick grass.

I suggest you troubleshoot the mower. After that, the blade should work fine when the grass gets thick.

Also, some mowers normally gets slow when grass gets thick, so after troubleshooting, if the mower does the same, then you already know it has to be slow when trying to cut thick grasses.

Take care

If the grass is very tall (more than 10") you will have to slow down to less than 1 mph, if you have a mulch kit on this unit, remove it to get the grass out as quickly as possible. Also, sharp blades & a level deck are important.

change the blade

You mention many PM issues but do not mention a blade sharpening. I don't get on my ZTR without a freshly honed blade installed. "That's" what cuts bahia grass...the blade. You can put all the horsepower you want behind the lade but if you're trying to cut grass with a 2X4 it rips more than cuts grass.