suddenly gone very lean

my yamaha cw50 suddenly started to run differently and pulled over it was smelling hot anyway took it steddy home put in a new plug took it for a spin and was very light brown so i whacking in a jet 10 bigger than before and still light brown making me think i have a air leek i have orded a new rubber inlet manifold but im worried it might be my crank seals or i dont really know its just it happened suddenly any pointer?

 

only way i know is to vacuum test the engine really for a accurate test without completly stripping it. how many miles has the bike done? if the bikes sitting for a few months then fired up the seals may have gone a bit brittle.

 

could spray some easi-start around. If the revs rise in a certain place there may be a leak there

BTW 2stroke...is that a KE125 in your avatar?

 

Yeah 1975 ke125, got giving it by a guy at work for parts for my kh125. It had sat around in his garden for 14 years absolutely fucked but was curious if ir had any life left ib it so I sprayed easy start through the carb and kicked it went first time!!! Decides to restore it instead of chop it up for parts. Added to my collection of 2t

 

Try resetting your mixture screw if it's running too lean, if that doesn't work then look for possible air leaks.
So many people on here don't set up their bikes, and just throw new parts at them in hope the problem will go away

 

i know ive jetted 4 peds now and i had it running slightly rich when checking the plug ,then it started being really hot now the plugs gone light brown i will have a look see at the mixture screw as ive never played with that but new crank seals are in with a new innlet manifold with the biggest jet i had 118 still lean