G'day mate, I run the same motor as you. I irk is great for throttle response. But you have to ride it more like a two stroke higher in the rev range if you want to maintain engine torque. Climbing hills for example you need to rev the bike harder. But I expected that. I think the valve springs are fine. You moto must be new so I'd probably go for the irk and upgrade the barrel and pistin to 140cc when you blow up the 138(127 really). We are already seeing a price war on all these parts, so make friends with Roost or ESD and get yourself a good deal. I have a question for you. Does your bike rev out propererly with the 30ml carb. I had to change to a 25ml to get it reving perfect.
Peace bro, ride on.
ive got both in my 138cc lifan and it goes so good now but id probly say do the irk first then see if u like it
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my ride: DHZ 138cc lifan. 55mm hc piston, inner rotor kit, pro taper bars, pro taper grips, kenda carlsbad front and back, ngk spark plug, dvs sticker kit