First, you meant combustion, not detonation. Detonation refers to the situation where petrol-air mixture burns much faster than usual. The ignition is timed so that the peak pressure normally occurs slightly after Top Dead Center, when the available space is increasing rapidly as the piston descends. Detonation brings forward the time when peak pressure occurs to approximately TDC, which results in an abnormally high peak pressure in the combustion chamber, accompanied by a knocking sound, which strangely enough is called a knock. In severe cases this sudden ultra-high pressure is prone to breaking piston crowns. Detonation is a severely destructive phenomenon, which at high speed can destroy pistons in less than 5 seconds from its onset.
Crankcase compression two stroke engines rely on a rather marginal process to scavenge the burned gas from the chamber after combustion. The momentum of moving columns of gas plays a key part, and at light throttle, when there isn't much incoming charge, scavenging is very poor and the engine will need a two or more successive attempts at scavenging before a combustible mixture will be achieved (called 4 stroking, or 6 stroking, or 8 stroking depending on how many tries it takes). One of the methods used to improve scavenging is to tune the exhaust system to produce pressure pulses timed so that there is a momentary low pressure at the exhaust port late in the exhaust process: this low pressure helps suck out the burned gas. Having a heavily baffled muffler right up against the exhaust port has the opposite effect: it messes up scavenging by causing a sustained positive pressure at the exhaust port (back pressure). This matters a lot more to a crankcase induction two stroke than it does to a four stroke. So, to get power from a crankcase induction two stroke what you would like to have is a pulse-tuned pipe (preferably tapered, megaphone-style). This is easily accommodated on a motorcycle but is a cost and packaging challenge on a lawnmower.
Any petrol engine will produce more power on less fuel if you raise the compression ratio, up to the point where detonation occurs, and provided you maintain the same volumetric efficiency. Power is also increased by improving scavenging efficiency, which in a crude baffled system can be brought about by omitting the baffle or making more or bigger holes in it. Of course this increases noise levels, which is a problem when there are laws about such things.
