So, 18 months later I figured I'll put an update to this little project.. it's come along a lot.
Starting with the suspension, I got a Fastace shock that was the right length and allowed preload and rebound adjustment, but the spring was a bit hard and it had too much compression damping. A new spring wasn't too expensive which helped soften the rear and I also had a go at stripping the shim stack and losing a few shims to soften the hit over bumps. Seemed to work pretty well. I guess a small bike is never going to be too plush on the bumpy lanes though.
Up front I've fitted a Race Tech emulator (well, a chinese copy of one) which needed an adaptor and different spring on the valve, but that works pretty well to be honest. The forks only damp on one side which speeds up changes if nothing else!
Aswell as the suspension, putting on a Michelin front, and Sava rear without inner tubes made a nice improvement to feel and cornering response. It is now handling pretty good, quite sharp and crisp. A bit frisky sometimes, but I like that, makes it feel more exciting!
Last winter it went on a diet. Originally it weighed 107kg without fuel, and I was aiming for 100kg. So, a new rear subframe using a Honda RS125 seat was made, small oil tank in the seat hump and Lithium battery and teeny rear light set up. The front end lost as much as possible from the steered mass, so it has twin lights from a Derbi GPR, and digital vapor dash with a modded TZR125 tacho. Losing all the weight from the forks made a huge improvement to the handling.
It now has an alloy front engine stay and bottom frame cross member which lost another kg.
I tried to strip it as far as possible while retaining the ease of use needed for a roadbike, so I'm really pleased that it's now down to 94kg without fuel, some 13kg less! With only 26ish hp on tap, that makes quite a difference to how the bike feels and accelerates.
A new pipe was made to be a little revvier and give better overrev. It only gained about 0.5hp, but the wider powerband and better revs made it racier to ride. The extra revs meant I could drop a tooth off the front sprocket without losing top speed, but gaining extra thrust for accelerating. Getting the jetting right started to get beyond the realms of normal jets, richer and richer it went, until I gave up buying them and just drilled them instead. 2.2mm felt good and gave good plug colour. 2.2mm is about size 600!
It also has a zeeltronic cdi.. it was meant for the TDR but I stuck it on the RS instead..
And recently I splashed some cash on a lightly used 170cc Athena top end for it. Most people reported a good increase in bottom end grunt but no real gain at peak hp. It turns out this is mainly due to the cylinder casting being the same as their 125cc cylinder, so it has 125cc sized ports. I opened them up to 170cc sized ports by widening the exhaust 5mm, and lifting the transfers about 1mm. The pipe stinger was made larger to suit too.
Initially the 170 kit felt awful, until I double checked the pv setting and found the spool must have a different end for DT's, as even with the pulley lined up, it was about 3mm closed. Once that was reset, it flew... I'm very impressed.. the bottom end makes cruising more relaxed, and the extra top end means it'll now hoist a wheelie in 2nd. Sadly the local dyno was sold off, so I've no idea how much power it's making, but I'd guess low 30's. How well the Athena top end will last, or if the fuel tap can flow enough (now up to 2.3mm main jet), or if the stock 50 rad can cope... we'll see..
So it's lost 13kg and gained maybe 5hp everywhere... I really like it!
