Category Archives: Yamaha YZF-R125

How to convert PCV maps to PC3USB easily (and free)

So I just figured some stuff about how to convert Power Commander V (PCV) maps to Power commander 3 USB (PC3USB) so I’ve done a little write up of it.

You can import older PC3USB maps into the PCV, and you can import PCV maps into the PCFC, but you can’t import PCV maps into the PC3USB, and you can’t import PCFC maps into the PCV.

Except now you can…and it’s super easy to do: Read more here

Autotune – game changer

(for me anyway)

There’s been quite a lot gone on here lately.. I’ve not posted for a variety of reasons which I’ll also get into along the way.

I’m trying to work through the backlog now and will have to post it in parts. This is part 1 – which is a little catchup on the autotune box I added to my bike recently, which we’ll build on for the next part/s.

I also realised that my email subscription thing on here is all messed up so till I get that figured out I’ve added a thing so you can login and comment with a account, as well as google and faceballs and whever other type of accounts. I hope that makes it easier to comment and ask questions etc.

The story so far

Continue reading Autotune – game changer

YZF-R125 injector swap

So there’s been a few discussions on the forums recently about different injectors, and I happened to film when I swapped my injector over so figured it might be useful.

It’s a pretty straightforward process…as long as you don’t mess it up.

At which point it would become very complicated. So really don’t do that.

I have a theory – that on a stock R125 which has perhaps a slip-on ((or full exhaust) and a K+n filter, that a 120cc/min injector would make a really cheap, convenient upgrade.

When mine was tuned like that the fuel map was adding about 20% across much of the map. Not all of it but enough for it to potentially make a difference where it matters.

And here’s the link to the 120cc/min injector. As far as I’m aware stock is 100cc/min, so that would give you a 20% bump across the range.I’ll just leave this link here:…

My problem currently is that I don’t have a stock bike to test the idea on…though I’m hoping i’ve found a volunteer. Watch this space 🙂

Cooking Clutches – R15 clutch upgrade for YZFR125. Attempt #2

Ok wow I’ve been working on this upgrade & video for months now – so it’s great to finally get it finished.

This is my step by step journey to upgrading the clutch on my YZF-R125 to the larger, stronger one used on the YZF-R15 (international version, 150cc standard), which is then further upgraded with a clutch boss with 6 uprated springs (vs 4 standard) which claims it can hold 2x as much power as the standard R15 clutch.

Continue reading Cooking Clutches – R15 clutch upgrade for YZFR125. Attempt #2

Fitting an extra temperature gauge to the YZF-R125

[I’m also moving this from the R125forum while there’s issues with it].

Some pics from fitting the temp probe and other randomness…

the temp probe.. it’s in what I believe is the return pipe for the radiator so whilst it’s not quite as good a location for temp as the main temp sensor, I haven’t got a reading from that and won’t have till I have the POD-300 controller/display so this is the next best thing and should tell me if she’s having a meltdown…

here’s my replacement section of pipe to replace the coolant pump return..hopefully it fits in the space.

Continue reading Fitting an extra temperature gauge to the YZF-R125

Baffled again..Exhaust tuning with custom baffle

My account on seems to have been deleted so I’m going to carry on here and transfer the last couple of posts..

I’ve had some work changes going on so been having to deal with that lately.. so not really had time to post about stuff, just do it.

Nearly 1k miles on the new cylinder and I’d been feeling with the old baffle in it was too restricted and losing power, and without any it’s still a bit overpiped and was losing the torque at the top end.

So I got some 2.5″ ali bar off ebay and cut a slice off and then made up some sort of baffle on the lathe, which looked more like the sort of diameter I was thinking might be good. One side is a bit tapered bc I was limited with the lathe bits I had, not really done much boring before, new bits on order will bring new possibilities.

Continue reading Baffled again..Exhaust tuning with custom baffle

Wideband O2 sensor on YZF-R125 with 180cc kit, for street tuning

Short video running through installing and testing my wideband O2 sensor to try and get the fuelling right on my YZF-R125 with 180cc kit. I was kinda nervous about hacking a big hole in my nice shiny stainless exhaust but I guess that’s part and parcel of getting into the more interesting tuning stuff…


LDPerformance wideband O2 sensor:

carbide grindy bits: (clutch diagram & parts):

6-spring clutch boss conversion from MOTOGAGA (untested, mine hasn’t arrived yet):


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Refitting the engine on the YZF-R125, now with 180cc big bore kit


not a lot to say here really – engine is rebuilt on the 180cc big bore kit, this is just putting it back in the bike..if it runs then we’re pretty much back in business!

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YZF-R125 engine rebuild (180cc big bore kit) – can I fix it?

This video is me trying to reassemble the broken motor for my YZF-R125, this time with a 180cc big bore kit. Link for the cylinder I bought (which looked *beautifully* machined):

Apart from that I only ended up buying the top cam chain guide and one replacement head bolt (which looked like it was going to round off) and a bunch of oil and filters. I’d bought a new cam chain too but hadn’t realised you have to split the bottom end casing to fit it..and you’re supposed to change the main shaft, cam chain and cam gear as a set, so i guess not this time.

Videos I found helpful for preparing the piston, rings and wrist pin etc:

wrist pin fitment (this was super useful):…

measuring ring gap:…

installing rings:…

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YZF-R125 Engine tear-down & failure analysis – what went wrong?