Why do some riding mowers die (especially MTD) when I try to engage blades at low and mid rpm?

[semimechanicman]

I’ve had a couple of riding mowers, which all have been MTD mowers. (Troy Bilt, Cub Cadet etc) It wasn’t all of them but some of them had to have the blades engaged at highest throttle or else the engine would die by itself.

When it first happened to me it was with a 2009 Troy Bilt Bronco with manual PTO. I started up the mower and tried to test the blades and I was in mid throttle, but when I tried to engage, the engine died and sounded like something like the blades got stuck or something. So I took the deck out again and checked for an stuck pulleys or bearing... they were all good and I could even move the belt and see the blades moving with my hands. I didn’t know what it was so I just put it back on and this time I engaged in full throttle and everything worked perfect. The engine didn’t stall or anything and the deck didn’t have any weird noises.

A few months later after selling that one, I had a Cub Cadet lt1018 (2004) I finished fixing it so I put the deck on and tried starting the blades up (I was also in mid throttle) and it died like something got stuck. I remembered the case with the Bronco I had and engaged the blades at full throttle and it also worked perfectly with no issues.

Ive had maybe 4 mowers (all MTD) do this thing but it was very minor, but I’m just curious. All mowers worked without any issues after that and we’re sold but I just want to know if it is normal or something was wrong.

 

[mechanic mark]

Read Operators Manuals from cover to cover first. Manuals will state that operator can engage PTO at full throttle. Very simple in laymans terms, follow instructions. Common sense, do not deviate from instructions. When you deviate from instructions there will be consequences, parts will start failing sooner than later

 

[StarTech]

Usually under powered mowers require full engagement. I have no problem engaging my Yard Machines (MTD) at mid throttle or lower but of it has a 21 hp ( originally a 16.5 hp was on it) powering a 42 deck which is currently using a 5/8" belt instead of the 1/2" the mower originally came with. I also cut 6-12" high grass at near full travel speed. Now the 3 foot or higher I have to slow down and cut half the mower width or I over load the deck discharge. Previously it was a gutless wonder when I was trying to cut my grass.

 

[Scrubcadet10]

My cub (Courage19) has no problem spinning the blades at low-mid RPM.

 

[cpurvis]

Engines that are not warmed up are more prone to do that. When the load is applied, the governor detects the decrease in rpm from the applied load and opens the throttle to bring the rpm back up. But that creates a lean condition and if not corrected with the choke, the engine will die.

Two of my three mowers exhibit this when not warmed up. The third is a diesel. Diesels aren't subject to lean conditions.

 

[ILENGINE]

Worked on a Poulan Pro years ago that would die if engaged at full throttle, and would run fine if engaged at idle and then brought up to full speed. Most likely due to newer engines with emissions making them run lean and can h'tandle the extra load when not completely warmed up.

 

[bertsmobile1]

It all depends upon the inertia of the engine.
Engines with heavy flywheels usually have enough stored energy to handle the blade load till the governor has opened the throttle and the engine has responded.

 

[howaya]

Could just as easily be the PTO safety switch. You can replace it with a new one or, if you prefer, bypass the switch. My MTD tractor needed two of the three safety switches dealt with this way.