Suzuki FXR150T
- Jan 8
- 5 min read
Updated: Jan 10
After working on some more parts for the CB125T over winter I decided if I was going to have a chance of actually keeping up with the fast guys at the kart track, or doing a half decent lap time at Timaru then I'd need a better chassis than that of the old Honda. I had made some straight intakes to replace the OEM ones, but didn't notice that in order for them to fit on the engine in the 125 frame, I'd need to either modify the frame or mount them on an angle... it was an easy decision to build a new bike rather than continue with something that was already fairly limited handling-wise.
As luck would have it a Suzuki FXR150 came up for sale just down the road from me for $800. It had already had the engine swapped for a 2 stroke GP100, as well as some other choice mods like wider wheels, aftermarket clip-ons and an RS125 seat. It was the perfect starting point for my new bucket, the chassis provided ample room for the Honda engine to be mounted between the frame spas and the design of the frame made it easier to adjust the carbs, remove the rocker cover and adjust valve clearances and work on the cam.
Mounting the Honda engine in the frame of the FXR was a bit of a mission if I'm honest. The frame was well painted from the previous owner, it took quite a bit of cutting and grinding to remove the engine mounts and paint from where I needed to weld. Getting the engine lined up was the next task, If I'm honest I didn't really do the best job of this and it'll probably required some tweaking in the future to get it perfect... I lined everything up off the rear axel, not sure why I decided that was the best option, I should have used the swing arm pivot as the reference as it's a fixed point. This is a perfect example of learning from your mistakes.
Regardless of weather I did it the right or wrong way, I thought I did a pretty good job of lining the engine up at the time. I made a mount for the front of the engine and tacked that into place on the frame. I had a dummy set of cases that I used to get the new rear mounts into position, I used my digital level on the rear axel, zeroed it, then moved the engine around using the clutch gasket surface as a reference, as I figured it should be pretty perpendicular to the countershaft axis. Once I had it pretty good I tacked the lower rear mounts into place and worked on the upper rear mounts to get it as straight up and down as I could. After I was happy with the alignment I welded them all up and called it good.
Whilst I was working on all the frame mounts, I had also spent some time building up a new bottom end for the new bike. I had taken the CB125 to the last round of C.A.M.S at Timaru at the end of the '24/'25 season and found that the gearing was way to short to keep up on the back straight even with the tallest sprocket combo I could find. After some googling and a bit of work on gear commander I figured out that I'd be able to use a CB250 "two fifty" transmission and cases with my 125 crank and top end and get a wider spread of gears for greater top speed at the big track.
The CB250 engine is practically identical to the 125, the mounting points are larger to accommodate larger mounting hardware, the transmission is beefed up with wider gears and longer countershaft. It doesn't have any provision for a kick start mechanism, not the end of the world for a race bike, and it turns out it's pretty easy to bump start. The final drive is taller too, with an extra friction plate in the clutch. Overall it's a better base for more power.
I ended up doing quiet a bit of work on the cylinder head and intake track on the new engine too, port matching the intake runners and ports, three angle valve job, back-cut valves and a new exhaust with larger header pipes.
There was a bit of faf involved once I had the engine fitted, the wheel alignment was well out of whack with both wheels biased to one side of the chassis. I had offset the Honda engine is offset left to right in the frame to mimic how it's mounted from factory, they do this to try and even up to weight distribution. But once I'd got it fitted the bike felt like it just wanted to fall over to the left, like the weight was biased to the left. Anyway long story short I moved the wheels centre of the frame to the rest of the frame and the bike no longer felt like it was going to fall over. Who would have thought...
The first time out on track with this bike was a revelation it handled so well when compared with the CB! It was predictable, with plenty of feedback both through the bars and the seat. I could tell if it was going to slide much sooner, when it did loose grip I didn't end up looking in the opposite direction, I could control it and carry on. That's not to say it didn't have any problems. A couple of races in I came to a very abrupt stop at the hairpin and it didn't take long to figure out why. One of the carbs had come completely off the intake and was just dangling on the throttle cable, a strange problem to have but I figured it was just the old Honda rubbers giving up the ghost and not clamping properly on the intakes. Turns out the timing rotor had come completely off, caused a backfire as the throttle was closed as I was slowing for a corner and popper the carb clean off! This wasn't the last time this would happen either... I managed to mount the carbs much more securely before my first trip to Timaru for the Southern Classic, and having done a full meeting with no issues I figured the timing rotor was a non issue too. It ended up coming off again on my qualifying lap, leaving me stranded on turn 5 and having to get trailered back to the pits!
Comments