suzuki 70cc not cooling down and sezing

Basically me and my dad spent the whole weekend putting a 70cc cast iron kit into my Suzuki katana ay50 LC. we also fitted a water pump repair kit and clutch springs and wavey disk , but ive got a massive problem with the barrel , it leaks a little tiny bit of resiude from the bottom left nut but its fine when running but the big problem is that it just keep stopping when running , for example im going along for about 3 minutes and the thing just feels like it gets tight and slows down and it turns itself off :/ and it does this frequently. i check if everything is okay and the waterpump is hotter than the standard exhaust but we checked the waterpump and everything is working okay , the water level isnt going down but the coolant feels like kettle water its that hot, so any one know what the problem is as this is staring to piss me off,

Regards :banghead:

 

if its leaking it needs a new gasket.

 

gasket is fine mate , now it hardly starts feels like there is compression but feels like the spark plug , will have a check but thanks