^^^ the temperatures inside the cyls are so much hotter when actually running full compression (at wot), that's what oxidizes the carbon off so well. When cruising the dynamic compression is usually between 3:1 and 5:1.
That's why the Onan Deere needs the heads off every couple years to brush off the carbon. 6:1 comp never gets hot enough, even air cooled, unless the grass is a foot tall. Also that's why a farm tractor never really runs smooth until you've plowed a field with it, gotta get it to open the governor and keep it open for a while.
Honestly it's the first 5 minutes after you start driving that the worst deposits occur, when it's harmful to drive hard and to boot the surfaces are cool enough for the incomplete combustion that forms elementary carbon in the first place. It'll self-clean enough if you drive a half-hour or more every day, but if you're driving 3 miles like me, it would take a trip across state before it gets rid of that buildup so I go full throttle a couple times a week after getting the motor good and hot.
Usually doesn't form on the intake tract. More where the injector sprays onto the back side of the valve, and its higher-than-average temp can cause the fuel to break down if the fuel concentration is sufficient and the airspeed (read: vapor pressure) is not. The worst hotspots aren't usually on the piston face, it's the flat face of the valve, which are much hotter. They only transmit heat into the head via the really thin seating surface.
detonation = super accel of flame front due to combustion pressure and after the spark plug sets it off, puts too much stress on rod bearings- this is what hotspots can cause, or bad gas + high comp; usually happens near TDC
preignition = compression + hotspots causes ignition during compression stroke before TDC and before spark plug fires, if you get this dieseling your motor is gonna be messed up quick, few actually run into this
Weight slows it down too, today between the 4 of us I know we were a good 200# over the limit of the car
. Felt like a Geo Metro.