Tag Archives: YZF-R125 tuning

Dakota Raceway 28th Sept, RWYB – [edit: event cancelled!]


I’ve just booked my 180cc bike into the RWYB at Dakota on the 28th sept. With the new RPM increase and some other changes I have yet to make I’m really curious (and excited) to see whether we can finally break 90 (i think yes), and if so how close we can get to 100mph.

Currently she’s capped at 11k which should put us at a geared max of 96.7mph, but so far I’ve not really seen the power band finish yet even with the 11k limit, so I’m thinking of adding another 500rpm and just praying i don’t melt the engine, which would potentially get us geared to 101.1mph.

Whether she’ll have the power to push that far I don’t know, whether I’ll end up melting everything and be left with no local transport and lots of new bills, I don’t know either. There’s gonna be a lot of “i don’t know”s in this experiment, some of them potentially quite expensive if they go the wrong way, but hey, life is risk, right?

So far with the local riding I’ve done she’s felt really good right up to the limit but I’ve not had chance to actually see about top speed, only in lower gears so far.

Also Dakota is an old runway and from the look of it is large blocks of concrete and definitely a “no prep” track/event. Apparently “they sweep it sometimes if they feel like it” which is very different from the fully-prepped (smooth as glass and glue on track for extra grip) Santa Pod which is the only other strip I’ve raced driven on.

Personally find no-prep more interesting/fun/dangerous since you have to actually take into account the track surface, lane choice etc rather than just twist the thing as hard as you can, so it’s actually more about rider skill than just who has the most ponies and money, but I suspect that it being less-than ideal conditions will affect achievable top speeds.

There do look to be a lot more small-cc bikes there so I’ll hopefully not stick out and feel as much of a wally there as I would on my little R125 at santa pod among the scoobies, skylines and superbikes.

Tbh if we can convincingly break 90 I’ll already be pleased, but if some of these new ECU tweaks pan out as hoped I think we might be able to do a little better than that.

Bear in mind this is still a 180cc with a stock head and valves, so we’re still using the small valves from the 125cc but trying to squeeze 40% more air in and out (80x/second!), and I’ve done *nothing* at all to the intake tract yet – stock throttle body, stock airbox etc, and no valve timing adjustment either, and all of those could make considerably more power.

So if we don’t hit 100mph this time, we’re certainly not out of things to still improve to get there, and if we DO get there, then we may well be able to push further than I’d ever hoped. And that’s before we even start down the road of forced induction, whether NOS, supercharger or turbo.

Given the rough surface at Dakota I think I won’t be switching to the “track” wheels with the sport demon tyres on and will just run my current combo which is a dualsport/all-terrain tyre on the back (Heidenau K60 Scout 130/80) and a winter tyre on the front (Heidenau K66 100/80). Somehow Heidenau tyres are unbelievably sticky but really hard-wearing. I don’t know how they do it. Both tyres have incredible grip in sketchy conditions, and ngl I sorta like the idea of rocking up to a drag strip on what are essentially dirt tyres on a somewhat “farm use” looking bike 😉 (especially if I’m then somewhat fast).

I was going to get all the newly painted plastics out of storage, and even had the boxes open and was looking at them, and whilst I’d love her to be in the right colours, looking as intended rather than the mishmash of random panels she’s wearing currently, the environment here is pretty brutal for a sportbike and until I have the facilities to repair/refinish them, I’d rather not trash my nice new panels amid the muck and gravel where my workshop is based, so I guess for now, patchwork bike on farm tyres ftw ¯\_(ツ)_/¯


Fastest R125-based bike?

I don’t know what the world record is for an R125-based bike (whether 125cc, 150cc or 180cc) – the fastest similar bike I know of is the Tuneboss Thailand one which has a turbo (but still somehow only makes 24hp??). They looked to be hitting 180kmh (111.8mph) but that was on a dyno with no wind resistance, so whether that would be the same on track I don’t know. Some dynos can calculate wind resistance and factor that into their power calculations but we didn’t see that, only the speed reading on the speedometer, which showed (an indicated) 180kmh.

It sure takes off though and as far as I’m aware, that’s currently the fastest…whether it’ll stay that way, remains to be seen.

If you know of another fast R125-based bike then please do let me know.

The only other thing I could find re fastest R125s was this video below on youtube which also shows the TuneBoss one as the fastest but also has another one which looks pretty spicy:

But those two are the fastest I can find and whilst I don’t think mine makes quite as impressive flames (though tbh I’ve generally been focussed on where I was going at the time so don’t actually know) I wonder if we might be in the running for at least being in the top 3 fastest R125s in the world, which would be awesome.

I was chatting briefly to a guy in france (or belgium, idr which) who had an R125-based bike apparently with hp in the 30s. He’d managed to squeeze a 250cc cylinder in there somehow but apparently he had to do quite a lot of work to the crank cases to make the cooling work (I’m not surprised!), but he wasn’t super communicative so I don’t really know much more about it than that. Pics or it didn’t happen.


Either way, I’ve just spent money which was earmarked for urgent drainage pipework for my workshop/living space, to go drag racing instead, so it’s pretty clear where my priorities lie ¯\_(ツ)_/¯

p.s. I just found this guy (Abhinav Bhatt) the other day and whilst he’s having the work done rather than doing it himself, he explains what’s going on really well and he’s doing some really interesting things with his later R15 which has the VVA engine and a 180cc kit. There’s a really good video of the (top end) engine build for that bike. With ~25hp it would also have to be in the running for fastest R125/R15 and he’s had quite a lot done to it. Check out his channel 🙂

YZF-R125 (180cc) – Swapping out the ECU to get an RPM limit increase, and hopefully higher top speed

So my bike keeps topping out at 89mph at which point we’re still on power but bouncing off the limiter.

Today we’re attempting to fit another OEM ECU, but which has been tweaked to increase the rev limiter to 11k.

If it works, it should increase our potential top speed to around 96.7mph – which would be a significant improvement, and also makes me wonder whether 100mph might actually be possible.

Will it work though, or will it result in fiery engine death?

Only one way to find out…

Removing lower timing gear on YZF-R125 attempt #2 – success!

This is the second attempt at removing the lower timing gear and the captive bearing on the crankshaft of my spare “B-motor”, which I’m trying to build up for my bike.

Idk if this is how it’s supposed to be done but I’m working with what I’ve got.

Whether this turns out to be a good approach or not long term remains to be seen but for now let’s see how far we get with it…

How not to remove lower timing gear on YZF-R125

This is the first of my “descent into madness” series of videos where I’m trying to rebuild this spare R125 engine.

I bought the engine as broken and when I took the cylinder off the bearing surface of the little end was damaged, which means the crank needs to be pressed apart to fit a new connecting rod.

So basically I have to take the entire engine completely apart just to get to this one dumb piece to replace it.

The videos are out of sequence but I have such a backlog and there was going to be a plan and it all went to crap. Every expert I was hoping to get to help me with this basically just disappeared or didn’t follow through, so I’ve finally resolved to buying the kit and figuring out how to do it myself.

Even though the engine in my bike has issues (from when I messed up a couple of years ago), despite that it’s done another 5k on the 180 cylinder (even wiht the timing chain issues) and I have not gone easy on it 😉

I’ve had a few people asking me to rebuild engines and do upgrades etc which is very cool, so it seems like it’ll be worth learning how to do it.

Hopefully this all ends with an engine dyno and building mad engines as was always the dream/plan 🙂 I’ve added this video to a new playlist for the B-motor rebuild so I can add all the other videos to it as I work through them. Thanks for watching and thanks to SXparts.com for sourcing hard-to-find components like the lower timing gear.


UPDATE: I said in the video (at 2:08) the lower timing gear wasn’t available, well it turns out i was wrong on that and you can get it here. Thanks to A for the link 🙂 https://www.cmsnl.com/products/sprock…

#YZFR125 #R125Life #bikelife #bikewife

I’m on Instagram – NEW R125 FRAME

Ok well you probably know how I feel about facebook products but if anything’s going to get me to cross that line it’s bikes. And it did..Actually so far I quite like it. Lots of nice picsand seems like lots of similarly bike-obsessed ppl but less noise than fb. Biker twitter has decidedly less outlaws than I was hoping for so perhaps Insta is a better place.

Either way..if you’re on there, of if we’ve seen you whilst out riding, please do follow + say hi 🙂

Let’s see if insta is a better outlet for my photos…

https://www.instagram.com/north_cust/

Also: this just happened:

For about a year I’ve been looking for a cheap frame to mount the turbo motor in, kinda because I was hoping it would be easier than making a motor stand..You sometimes see written off frames o ebay for peanuts and I was hoping to get one and perhaps cut out what I needed if it couldn’t be put onthe road anyway. You can get clean frames with paperwork from italy and germany but they’re usually £500+ and that’s a bit much to spend on somethign wich may never even make it to he road…but then at long last I found this one the other day in Germany.

Continue reading I’m on Instagram – NEW R125 FRAME

Making a new fuel map for bigger injector with PCV & Autotune, on yamaha YZFR125

This video follows on from my last one and goes through the process of building a new fuel map from scratch for my 180cc YZF-R125, the way I do it, using the Dynojet Power Commander V (PCV) and Autotune (with a wideband 02 sensor).

We go through all the various components/electronic gizmos and how they interact to get to the end result of a tuned bike.

I hope this makes sense cos I had to make a bunch of diagrams and stuff for it which took forever lol xD

This video is focussed on tuning using a PCV and Autotune which is a setup that seems to be working well for me, and for this sort of moderate tuning.

I know many of you have PCFC/PC3USB etc which is a little different and can’t use autotune, and the next video will be about what your options are in that case. Thanks for your patience and I hope it’s helpful 🙂

IF YOU’RE INTERESTED IN FUEL MAPPING:

Please check out this interview I did with DynoJet UK – we covered some really interesting ground – especially if you’re thinking of buying a Power Commander (who make the Power Commanders).