The carb on my PGO Big Max 50 was knackered with stripped threads on the float bowl and mixture screw. I spoke with the guys at 'Pedparts' and opted for the 19mm TNT 'Racing' carb as it had various jets etc included making it easier to set up. I also got a 'Speedfight' adaptor to connect to my existing manifold. I removed the stock jet and fitted the '85' that came with the carb. When removing the float bowl I noticed two spring washers under two of the bolts. I put the float bowl back on and refitted the bolts (including the ones with two washers). When I fitted the carb, I noticed the float bowl gasket leaking. On inspection it seems that there is interference between the main jet and its shroud and the float bowl, thus preventing the bowl seating properly! In the carb body, two of the float bowl bolt holes are clear, the others are 'blind' yet all the bolts are the same size, ie: two are slightly too long, I've ground them down, maybe I'll have to do the same with the main jet!
this is the same that happened to me! i have sent it back and still not heard anything yet i would suggest doing the same!