MOPED ARMY

You probably won't find too much help with your Spree here, since most of us are into mopeds and not scooters. -- but on a more general level, cutting the muffler off was a pretty bad idea. My advice would be to put a new muffler on it.

Well, 2-strokes aren't like 4-strokes. In a 4-stroke engine, the exhaust just provides restriction to gas flow (in exchange for sound deadening and some measure of cleaning), so it robs power from the engine. In that case, you might see a power increase from removing the exhaust, even though that's probably illegal in your state.

The 2-stroke engine, however, relies on complex gas dynamics to operate. Rather than using the two extra non-power strokes to purge exhaust and compress the fuel-air mixture, the engine exhausts on the power stroke and draws in mixture on the compression stroke. These engines would be horribly inefficient without some back pressure, because all the gas would rush out the open exhaust port during combustion. In the early days, this back pressure was a tuning compromise bewteen not exhausting enough spent fuel and losing too much compression. (your old pipe provided this restriction)

Then some clever lad figured out that the gaping hole in the side of the chamber that all the expanding combustion gas leaks out of could be temporarily blocked by a pressure wave of gas coming back into the engine from the exhaust line.

It's very clever, really- if you know the timing of the engine firing (which is dependent on RPM), and you know the velocity of the exhaust gas (which you do, because you know the engine displacement and RPM), you can make the gas shock wave travel down a pipe and reflect back into the engine to increase pressure in the combustion chamber only when you need it.

And that increase in pressure equals an increase in work, and more power out. (more power out equals mad wheelies and burnouts)

Race pipes designed especially for this are called 'tuned pipes' or 'power pipes', and they cost three to four times what a comparable 4-stroke exhaust would cost, because they are specially designed to reflect the shock waves back up the pipe at a usable RPM. The bulbous part of the pipe right before the restriction reflects part of the gas shock wave to the combustion chamber.

You could attempt to get one of these pipes and hot-rod your moped. (Beware- this is naughty in the eyes of the state and may cause noise trouble with the neighbors to boot...) However, be advised that if you succeed, you may hole a piston or snap a crank with your newfound power. Or you may plow headlong into that idiot who pulls out in front of you, because your weedy brakes are only meant to stop you from the blistering speed of 30 MPH. Or you could discover that your carb isn't feeding your new hungry cylinder enough gas, and you have to find a new one.

Your other option, the safe one, and the one the Man wants you to take, is to put the stock exhaust for your bike back on it to keep the MPG up and the MPH down. I'd encourage you to do what your soul tells you (hot-rod the beast) but use caution.

Whichever option you choose, please wear a decent helmet. We can't afford to lose any more 2-stroke nuts- the cell-phone using motorists have thinned the herd enough already.

Power to the Pipe! Swarm and Destroy!

Not that a lot of what you said does not apply, but I think the spree is a 4 cycle.

Anyway, I like Miguel's advice.

Ron

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Down and to the left, thanks.