Overfilled motor oil on ATV

So I am on the road currently and my Son tells me that the oil level in the quad is low. So I tell him to drain it (Ends up draining the Trans fluid, which he measure the right amount and replace correctly with 10w-30.) So He still put motor oil in the engine, and he fills it up all the way to the top to where he almost overfilled it. After replacing trans oil and with the motor oil filled all the way to the top, he started it up and he said the quad couldnt accelerate past 2 mph, no leaks he said. Is it because everything is over lubricated causing problems? It smokes overly in the exhaust when accelerated and smells like crazy he said. So is it the engine itself or just the overrly amount of motor oil. (Probably 1.5 quarts more the required)

Please help!

Dont worry, I told him to cover it up till I get back.