The tuned pipe can increase volumetric efficiency quite aggressively at resonance if set up properly - it is simply acoustic supercharging, meaning that it increases the pressure and thus density of the incoming fuel/air mixture. All depends how the porting/timing is set up. Two strokes run fine open exhaust or with simple expansion mufflers. The tuned pipe is not required, it is not a case of you "must" use it. when it starts to get really powerful, turn the screw out until you notice a decrease in power. now, do the same with the high speed circuit, except when you do this, have it at wide open throttle. keep tightening it slowly, until it bogs down, or quits, now loosen it 1/4 of a turn, no more, no less. now, with the motor running, you will want to tighten the screw very slowly, and you should notice a difference in the speed of the engine. once it starts, it should promptly die when you try to give it throttle. if it does not start, you will need to close it again, and turn it out two and a half again, prime it, and loosen the screw 1/4 turn at a time. it should at least sputter, if not, then tighten the screw 1/4 of a turn, and try again. attempt to start the motor after priming it, by pressing the rubber button 3-4 times. Then, turn the L screw counter clockwise two and a half turns, opening the passage for the idle circuit. you will want to gently turn both screws clockwise, closing off the fuel to the engine. L stand for low speed (idle) and the H stands for high speed. on the body of the carb, you should see two screws, labeled L, and H. next, you will need to remove a plastic shroud that sits in front of the carburetor.
I removed the bar, because it was in the way. safety first, you will need to remove the chain, and bar from the motor. the engine I am using is from my chainsaw, which is a Husqvarna. So folks, let's get down to the nitty gritty. The burning fuel expands, driving the piston downward, to complete the cycle. At the top of the stroke the spark plug ignites the fuel mixture. (At the same time, another intake stroke is happening beneath the piston). The piston then rises, driven by flywheel momentum, and compresses the fuel mixture, insuring that the mixture explodes properly.
so, you think an exhaust pipe is just meant to get the exhaust away from the engine, right? well in the 4 stroke application that's completely true, but in the two stroke, you must use a specially formed pipe, that uses something called backpressure, to force the expelled mixture back into the combustion chamber, this can be seen in the animation quite clearly. I'm going to interrupt here for a second to explain how that fresh mixture is prevented from being expelled. Unfortunately, some of the fresh fuel mixture is usually expelled as well.
This expels the exhaust gasses out the exhaust port, usually located on the opposite side of the cylinder. Toward the end of the stroke, the piston exposes the intake port, allowing the compressed fuel/air mixture in the crankcase to escape around the piston into the main cylinder. The fuel mixture is then compressed in the crankcase during the remainder of the stroke. During the downward stroke the poppet valve is forced closed by the increased crankcase pressure. The illustrated engine features a poppet intake valve, however many engines use a rotary value incorporated into the crankshaft. Intake, The fuel/air mixture is first drawn into the crankcase by the vacuum created during the upward stroke of the piston. 2 is the fact that they have fewer moving parts, which decreases the constant load on the engine, allowing it to burn the air-fuel mixture more efficiently, and reach much higher revolutions per minute. 1 is the displacement, they generally have smaller combustion chambers, which means less fuel burned. Two stroke motors are more efficient that four strokes for a few reasons. Here is an overview of how two stroke motors work.
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