Tucomse moer 5.5 Won't speed up when cutting tall grass.

YOU ARE CUTTING TO TALL OF GRASS

Protection for motor. If you cut tall grass the blade spins slower and motor uses more electricity which makes it get hotter faster. When it reaches a critical high temp it will shut down till it cools lest the windings will melt the insulation and render motor useless.

Only way around this is not not let the grass grow so tall that the motor labors and slows down appreciably.

If gas motor, it is overheating and the internal engine parts are expanding, increasing internal friction and eventually stop the motor.

Grass is too thick & tall and may require a second pass until next time when it'll be easier to cut, or... blades are dull & need resharpening, or... tractor speed too high for the length of the grass.

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.

If you are cutting to much grass this can happen or if the throttle control is not in fast speed (rabbit). If it is in slow speed (turtle) it will tend to die down in tall grass or wet grass. Good Luck...

Typically, wet grass or tall grass will get caught. Mow only when dry and make sure your blades are sharp. Mow with the engine at full speed [VERY IMPORTANT] adjust your ground speed by using the proper gear for your conditions. With the engine at full throttle, choose a lower gear when cutting higher grass. Make sure the air outlet of the rear bagger is unobstructed. It has to be able to breathe.

I trust you will find use of these techniques will lessen the clogging rate you are experiencing.

Thank you for your question @ FixYa.com

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.

if it has a grass box,mow without it and then mow again with box or use a strimmer and then mow.

Is this the first time cutting grass with a lawn tractor?
How tall of grass?
Use the grass cutting heigth adjustments on the tractor to a higher setting when cutting tall grass. Cut again to a lower height setting on the second pass. Grass higher than your tractor is not good for your tractor. Follow the manual instructions for best results.

I've noticed that when the blade get dull it work harder a cutting tall grass. I just put a new blade on mine and now it runs and sounds like a brand new mower. also if the inside of the deck is coated with old grass that makes a differance too