I'm pretty sure "mine" ( ie the wife's ) does 100 easily enough... altho I never rode it anywhere much - ( most my local roads in sai kung are 70 at most so I do 85 on them - i never took it on the highway since I never had need to - altho I wouldnt hesitate if I had too )
metal ash? - well ash is sometimes a mistranslation of smoke... so basically he's saying its burning some oil? is this the new oil you just had put in.. can you see the colour of the oil in the inspection window... takes a while for it to go black usually...
and 2 liters? hmm that would put a lot of pressure on the inside of the engine............ ( some people just shouldnt have motorbikes!!!!! )
which gasket did he change? at the front you say? ( blowing due massive pressure build up - too much oil )
( would that be the head gasket? or the base gasket? in which case he's had the piston off.......... shame you cant ask him.. )
is this a fuel issue? maybe the carb wants a clean? - altho I would have thought you would have issues in other gears at top of rev in that case.. ie reving the b0LL0x off it - is it ok?
other factors could be a breather hose - but again that would affect other gears?
new spark plug should only be HK$ 50 -90 depending on brand - so thats no big deal
hopefully someone on the forum can shed some light on my stabs in the dark.
alternativley before you give up call Yuen at ACE motors - just on the other side of cross harbour tunnel -
speaks english and is cheap too.....