52mm build  By  imarider (Read 1,390 times)

1 gasket and the piston hits the head. Millsc told me to use two and like magic no hitting.

There is no exact answer as jetting requires trial and error . Rather than pay per jet I would get a jet kit with many sizes to test out like this one jets If you look on Amazon you can often find NGK sparkplug packages which is cheaper than buying individually so that you can do many plug chops and keep them for later use . Here is a great chart to compare your plug tips with plug chart . R&R the plug after idling , 1/4 , 1/2 and 4/4 which is WOT . Hopefully your carb you can adjust the air/fuel screw and needle clip . If you already have the carb and a caliber to measure the jet dimensions , go here to verify that you carb uses the same type of jets as most 139QMB carbs do jet identify

I used an Air Sal 50mm BBK that used the stock 49cc head and two gaskets as compression is higher with the smaller combustion chambers than on a 50mm or 52mm head . The bigger heads should have larger valves and ports . I hear great reviews on the custom head from Scrappydogs here at the top of the page Scrappydogs

I have seen a few online and many local riders who have a 2T exhaust pipe on their 4T and no muffler . They have been rejetted and do not pop , not as loud as I would have thought , has a nice mini thumper exhaust note and performs better . I first saw this on a Keeway Matrix which is normally a 2T Minarelli scooter but my dealer had one with a GY6 150 with a 2T pipe . I guess it was one of those " sleeper " mopeds .

The stock crank may hold up unless you are abusive and the bearings go out . Look into getting a Hoca or Nakaru stroker crank for another day