In early 2024 I started building up a bucket racer for the coming season's racing at the local kart track. The bike was in a bit of a sorry state, no brakes, forks were partially disassembled, engine had low compression on one of the cylinders and so on... I got the bike for free so I can't complain too much. The bike is based on a CB125T, the wheels and front end are from a TZR250 2MA.

I stripped the top end off the engine, the left piston looked pretty knackered. It'd had a seizure at some point. I had a second engine that came with a half decent set of pistons and cylinders. I gave the bores a quick hone, chucked a set of rings on the pistons - just to get an engine together so I could get it running and start going through what needed doing with the carbs, ignition system etc...

In and around working on the engine, I started making an exhaust and sorting out the brakes and suspension. I had a dummy engine in the bike that I could get in and out easily (nice and lightweight, no internal components) so I could mock up an exhaust. Lucky for me, I was working at a Yamaha dealer and there was an old set of header pipes from an R3 already chopped up in the scrap bin, I commandeered the pieces and cobbled together a 2 into 1 system mated to a $50 AliExpress muffler.

At this point the bike is pretty much ready to go, it's running and I've ridden it up and down the driveway. I took it down to the dyno at MCR so I could run it up properly, get some temperature into the engine and get an idea of what sort of power the bike was making. The first few runs went okay, the fuelling was way off (I'd bought some cheap carbs from Trade Me that were intended for a single cylinder 125). Before I could start swapping jets the bike just died... no spark. To cut a long storey short, the bike came running a TCI module from an old XJ750, it had decided to give up the ghost so that was game over for that tuning session.

In a bid to get the bike running and riding for the first race of the season, I cobbled together a set points, found some old coils that'd work and got them married up to the bike. They seemed to work okay although, they took a long time to set up and they seemed to float at high rpm giving an irritating misfire... they got me through the first round at the kart track which is all that matters!

I turned to my old friend AliExpress, turns out you can buy an electronic ignition set up for a Honda CB500 four that is very close to 125 setup. It basically goes in place of your points and you can use the same coils, pretty much plug in and play. There was a bit of fiddling with the backing plate to make it work on the 125, also the magnet supplied in the kit was crap... so I ended up using the ignition rotor from an XR200 instead which worked perfectly.