KX125 '98 tuning. big bore?/port timing? HELP!!

[alanreeves]

I am converting my mxer into an enduro machine, which is going fine but...
I feel the way the power kicks in the midrange is gonna catch me out on some of the more tricky stuff, and it's a bit low on torque. I want tuning options which will smooth the hit out and increase low end torque without losing any top end.
Would having the ports altered/polishd be enough? or...
I was considering a big bore conversion but what is maximum cc to still be legal in the 125 class? and how much reliability would it loose?
What do you think of flywheel weights? To me on a 125 it doesn't seem like the way to go.

 

[EricGorr]

Hi Allan,
That bike has an inherent problem with the KIPS valves ****ing and jamming in the full open position, which causes a huge loss of low end. Pro Cicuit makes a valve cover that prevents that from happening. Contact PC UK for the part.
Regarding maximum displacement for enduro racing in the UK, I have no idea what your rules allow, I don't think it can be bigger than 125cc. In America the AMA combines many off-road classes like 125-200cc so that allows us to big bore to 133 or 144cc.
Good luck

 

[alanreeves]

FAO Eric Gorr

Would that be the front cover or the side one?

 

[alanreeves]

EricGorr please reply

I've not had much chance to ride the bike yet so I've not experienced this problem but what about modifications to the cylinder and/or cylinder head without a big bore, as the limit as you said is 125cc? I dont want to lose out on any top end (gain some if possible) but would like more torque.:think

 

[marcusgunby]

The cover eric talking about is the top one-you can modify the std on by drilling and tapping it(look at the PC desgn to get the basic idea)
Eric can port your std cylinder for better torque-i used his porting specs on a 98 and it was alot better but only after fitting a FMF fatty pipe-with the std pipe it was held back.One thing was even when tuned the KX's power seems to kick in with a bit of a hit and this makes it a little hard to ride.