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My toro 75755 with the toro 24.5 hp motor, will throw black smoke and will start to shut down at half throttle. At full throttle it will run better but still not great. I changed the plugs as they had a dry black heavy soot on them. I drained the gas and put fresh in, I changed the fuel filter, plugs and fuel pump. It is still running like crap.

Running rich. something wrong with the carb. Poosibly a jet has fallen out causing it to pull in too much gas under load. Just as a side note also make sure the oil doesn't smell like gas, because gas fumes from the crankcase can cause similar issues.

Angles1610 said:

My toro 75755 with the toro 24.5 hp motor, will throw black smoke and will start to shut down at half throttle. At full throttle it will run better but still not great. I changed the plugs as they had a dry black heavy soot on them. I drained the gas and put fresh in, I changed the fuel filter, plugs and fuel pump. It is still running like crap.

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How many hours on engine and year and model of engine?

Good possibility the coils are weak and failing. I am working on a customer mower with Kohler Command right now exhibiting similar symptoms. Black, powdery spark plugs, running rich, occasional black smoke, low on power, idles poorly and better at WOT. Ohmed out coils and they are on order. Took a bit to diagnose and checked several things before ordering coils.

I owned two Toro mowers with the same engine. That particular engine has a two barrel carburetor and has a paper air filter and foam pre-filter. It’s very important to keep that foam pre-filter clean. I would blow out the foam pre-filter after every mowing. Both should be changed yearly or at 100 hours, whichever comes first.
It’s also a good idea to blow off the entire mower and engine after each mowing.

just worked on one yesterday. It has 2 jets one for each cylinder. Remove the jets and tubes clean the small holes

NorthBama said:

just worked on one yesterday. It has 2 jets one for each cylinder. Remove the jets and tubes clean the small holes

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You are talking about a two barrel Nikki carburetor and actually has slightly different size main jets. There is a Walbro carburetor on the mower I am working on. Usually it is a lean running condition that requires a carb clean. Running rich is a choke not opening correctly, float position problem, or possibly accelerator pump, if equipped.