I'm having trouble finding a performance muffler and do not know how much to trust the vendor when he says "yes it fits and no it's not too loud". Police here are very strict and sometimes even have decibel-meters in their car!
Seeing as the general idea is to facilitate gas flow by reducing resistance, an oem muffler made for a 250cc for example must flow more gas than an oem 125 muffler, right? And much quieter than a free flow aftermarket muffler.
Cutting and welding downpipe and brackets wil, of course be necessary and much less obvious even for the official county technical control mechanics.
No other choice really if you cannot find OEM weight on internet. Measure the rollers installed, try all 6 together on kitchen scales. 6 x 24g = 144g, 6 x 23g = 138g etc. Perhaps Dr.Pulley can help? Then order 1g or 1.5g lighter for sliders for smoother acceleration.
ps: Most 2 or 4 stroke scooters from Asia all made roughly the same way, just the Italians are a little different.
I wonder if you have the head off or just separated enough to look, you can turn the crankshaft until the piston is at top. Then find the position where the cam is not opening any valves, you'll have between 60° and 80° of free mouvement according to some web posts. Having found TDC you can reset the valves to factory clearances to start then turn it over by hand to check no valve tapping against the cylinder. Just my penny's worth...
Wow, this job made me suffer. When I deemed myself ready to attack the head again, I took a day off on overtime hours. The evening before I stripped off body panels and modified some lugs on the flat floor panel with a cutter so as not to have to take off the whole rear end the next time. Up early, all the EGR pipes were soon disconnected, pipe, carb and inlet studs also.
The head was transferred to the kitchen where it was warmer than the 5°C in the garage! Here, the valves were taken out and I unfroze my fingers.
Here in Switzerland, most apartment buildings have atomic shelters under the garage, they are actually used by residents as cellars or storage rooms. So the grinding and matching took place down in our "cave" (french for cellar, UK expat liiving in french speaking region). The valves remounted and all cleaned.
When I had put all back together, turned it over by hand then by kick, I fired it up only to have a horrible clacking sound. Investigation revealed that the chap who had mounted my winter tyres had oover tightenend one exhaust nut partially pulling out the stud, thus gas leaking. So I dismounted the head again and drilled and tapped a bigger (8mm) hole, installed a 8mm bolt with loc-tite then cut it off with the Dremel to the right length. I drilled out and retapped one of the exhaust nuts which were derusted and painted. All was put back again and she fired up fine. I've only had time to warm her up in the garage but will test on the road of course. Here she is now ready for the cold season, leg protection for me and winter tyres for her along with a belly full of new 10w40.
Oil consumption is low, I'm at 9k km, stop/start city centre short journies. A little inlet manifold matching will be done next time as well as cleaning inlet side gunge and exhaust side coke. Very similar to Yamaha cylinder heads.
Strangely enough, I've noticed that putting the valve clearances closer to 0.010 than 0.015 (recommended 0.012 +/- 0.002) has reduced idle speed and pulling power WOT uphill. I'll put them back closer to a tight 0.015 where the motor seemed happier before, just a llittle tappet noise...