well if the head is going to come off you may as well do the valves and check the cylinder for scoring while you're in there. That would take care of most problems that could resemble a bad head gasket.
you just need one from a scooter with a wheel the same diameter as yours. There mostly inaccurate anyway. some scooters come from the factory with the wrong puck or tires to small. consider a gps phone app
the stock cam is already pretty good and is not actually the problem most of the time. I have found that the stock valve spring actually starts to float at 5000 rpm on a 150 it still makes power at higher rpm but it's limited and not very good. I think perhaps this is why many gy6 have a 5000 rpm limited ignition. Stiff springs is a possibility and will even help a lot. I have found it much better however to use stock springs and instead cut and polish the rocker arms and replace the valve spring retainer with titanium. The cam following pad is massively over sized and can be trimmed significantly. all this has the benefit of significant power increase without the extra frictional loss and increased wear from heavy spring pressure
Last Edit: Mar 28, 2021 2:01:35 GMT -5 by chewbaca
A heavy clutch spring does exactly the same thing as a light veriator weight except it causes more friction in the belt. It should really only be used if you have so much extra power that your belt is slipping. Just match up your V-weight to your best torque rpm. 5000 to 6000 rpm is peak torque for a stock 50 and it drops with more displacement, drastically with stroke but hardly at all with bore.
the 3 clutch weight springs change the engagement rpm and you should always have the engagement rpm as close as possible to the veriator shift rpm without going over. Cutting the clutch weights is far superior if more difficult to do correctly.
Last Edit: Mar 28, 2021 1:29:45 GMT -5 by chewbaca
I am not exactly sure of what you are saying but if you use an oil catch canister and plum the valve cover vent through that and into the intake manifold as opposed to the air box you can induce a slight vacuum in the crank case thereby reducing pumping losses and eliminating oil leaks
they are functionally equivalent With the flat gasket providing slightly more resistance to flex than ring. most of the exhaust pipe is too poorly made for that to matter anyway. if you want to do something that matters take a dremel and smooth out the throat of the pipe. a clean smooth transition is very important when going from large to small diameter pipe.