Anyone could put this together with a hacksaw and a few minutes at the muffler shop. Takes me 3 months...
The pocketbike pipes have a 22mm downtube. The 19mm Spree downtube fits inside this nicely. I notched the larger tube slightly and inserted the Spree into it. Nice tight fit. Then I tack welded it in place and went for a ride. I should have just bolted it up, checked fit/angle, then taken it back to work for final welding. More on that. Let's say for now I was impatient.
I should note now that the Spree has a bad back tire (brand new Chen Shin, out of round) so I haven't been riding it, it bounces down the street if I do. I warmed it up and went for a ride, with the backend bouncing. Very loud. Seems to lose some midrange but is breathing nicely. As I approach 30 (top speed currently 28) I hear a loud "clang" and a roaring sound. Look behind me to see the expansion pipe bouncing down the road after me; the spot welds had broken. It finally stops under a parked car. Hilarious. I walked the scoot the rest of the way home.
The final version needs full welding and an L-bracket support to the engine case to keep the pipe from breaking the jug over time (too much torque at the exhaust port otherwise.)
The other reason I didn't finish the welding: While this is the easiest version to build, it's not quite correct. Ideally, the Spree downpipe should be the same length as the original downpipe, which was around 9.5". It's currently 11.5" or so. To correct this, I'd need to cut the pocketbike expansion chamber at an angle, reweld it, and attach it to the cut-down Spree pipe. This may or may not actually happen, but if I build it, I'll post it.
