Tag Archives: Yamaha YZF-R125

My First Drag Racing Win on YZF-R125 @ Dakota Raceway

August 19, 2025 northcust Leave a comment

So whilst most of the day was everyone racing individually against the clock, they did have an optional “knockout” competition in the afternoon, where each bike has a handicap based on the times you’ve run so far.

This is 1/8mile (660ft) no-prep sprint racing on an airfield and my first time out racing on a bike.

So as far as I understood the rules: with this knockout thing if you’ve been running 10s and someone else has been running 8s, they’ll get a 2sec delay on the start and have to chase you down. If both bikes have a good run they should cross the finish at the same time.

So it lets mismatched bikes run sorta fairly, which is pretty neat. If you make any mistakes and the other guy doesn’t..you’re out.

The survivors of each round go into the next.

If you somehow run better than your best time so far, you knock yourself out, which is random but an interesting twist (similar to “bracket racing” i think).

I’d been running early 11s all day and the scooter I was racing was much faster, running 8s, and somehow despite my start I got there before he could chase me down 🙂

That was only the first round of the comp and I very much lost the next race, but hey. A win, ANY win first time out is a nice thing, so I’m happy 🙂

Bizarrely it was actually my slowest run of the day (11.6).

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This is on my gen1 (2008) YZF-R125, 180cc, still; on the PCV+autotune setup with the RPM limit raised to 11.5K on the OEM ECU.

#YZFR125 #YZFR125tuner #YZFR125racing #YZFR125sprint #northCust #NationalSprintAssociation

Racing

RWYB at Dakota, 16th August

August 11, 2025 northcust Leave a comment

So, with a bit of luck we should be drag racing this weekend at Dakota Raceway in South-west England.

This should be quite good timing as this is as far as I’m planning to go with the current tuning setup (PCV + Autotune, 11.5k limit) so it should be a nice benchmark of how far we’ve come.

Assuming the bike (and rider) are still functional afterwards, I’ll hopefully be taking the bike apart and doing a bunch of updates, including switching to a tuneboss-based ECU setup which ought to make tweaking the ignition timing a lot simpler and also add a quickshifter.

I also feel like the timing chain has maybe stretched somewhat and is pushing the power band higher than I’d like, and we’ll hopefully be fitting an adjustable top gear (vernier cam pulley) to correct that.

With a bit of luck I should have some help from a friend at Sword & Fiddle Productions who should be filming the whole thing (thank you!), so with a bit of luck we should have some cool footage afterwards. Also thank you to my other sponsor NewJerseyIsALifestyle.com

I don’t really know of any other real-world testing (videos/timing) of R125s so I’m very interested to see how we do. For me this will serve as a reference point, and perhaps once the bike updates are done we can try again and see how we do in comparison.

I put the bike on the roller the other week and tbh it felt great so let’s see what it can do 🙂

It’s 1/8th mile racing rather than 1/4 mile, so we likely won’t be setting any top-speed records and will likely have to gear right down in order max out before the finish, but the plan is to start off on a 14t (normally I run 15t), till I’m used to the track and then gear down to 13t if needed. Hopefully that means times should improve towards the end of the day.

If you’re planning to attend the event, either racing or spectating, please do come and say hi 🙂

Below is a quick clip of how she was running…seemed to have power to the limiter so let’s see how we do!

B-motor, Yamaha YZF-R125

YZF R125 180cc kit top speed

June 11, 2022 northcust 2 Comments

TL;DR: Top speed I’ve managed (so far) on my gen1 with 180cc kit, 160cc injector and longer duration cam, with PCV + Autotune/wideband: 89mph at which point we’re still on power but bouncing off the rev limiter.

UPDATE (4/8/2024): I’ve just increased the RPM limiter from 10.1k (standard, according to the ECU itself, not hearsay) to 11k, which should give us a new top speed of 96mph – I’m awaiting an opportunity to test this as with the rebuilt 180cc engine with the rebalanced internals (forged con-rod and lightened crank pin) she’s still very much in the power band at the previous RPM limit of 10.1K. At the time of writing this i’ve only ridden it once with the new limit and it was only locally but she pulled all the way to 11k so I’m hoping we can get close to the theoretical 96mph. I’m gradually getting a bit more set up in my new location and this is something I’m going to be working on in coming weeks/months, so watch this space, and my youtube channel for updates. I think with a little more work 100mph will be possible.

Please note: just raising your RPM limit may not be wise and may destroy your engine, especially on a 180cc kit since it changes the engine’s internal balance factor. I’m doing it here because I’ve built this engine a certain way which means the power band actually comes in a little higher than stock, so when we were hitting the limiter before we were still very much in the power band, and the engine wasn’t shaking or sounding unhappy, in fact it was smooth and in “mechanical harmony” (best way I can describe it). You can probably go a little higher on a stock engine (e.g. 500rpm) but mine is most definitely not a stock engine, so don’t try this at home kids, unless you know what you’re doing.

Info re RPM limiter coming direct from the ECU. The box we’re looking at is on the right where it shows the high limit is 10.1k, not 10.5K as is often (wrongly) assumed. My tacho showed 10.5k as the limiter, but apparently it also isn’t that accurate.

So I’ve noticed there’s people searching on this topic so I’ll share what I’ve discovered so far, hopefully it’s of some use.

Top speed on mine when I got it, as 125cc on stock 14t sprocket was 83mph (indicated). That was absolutely throwing-it-down-a-hill-with-the-wind-behind-you, the most I could get out of it. 83 seems to be a fairly common top speed for stock bikes. Some other people have claimed 86 out of a stock bike but I can’t verify that myself and that wasn’t my experience and speedo variations could account for the difference.

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I’m on Instagram – NEW R125 FRAME

August 6, 2021 northcust Leave a comment

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.

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Yamaha YZF-R125

YAMAHA YZF-R125 ADJUSTABLE CNC brake levers

April 21, 2019 northcust Leave a comment

Whilst my thus-far pitiful efforts to pop dank wheelies are still going unrewarded, trying to do so highlighted some issues with my hand controls.

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Yamaha YZF-R125

Debunking airbox mods On Yamaha YZF-R125? – part 1

April 19, 2019 northcust 2 Comments

Ok so this seems to be an ongoing urban myth, whether it’s chavs drilling the airbox of their mum’s Fiesta 1.1 popular or little 125s, or even big bikes, people seem set on the idea that airbox designers are actually our mums who are trying to sneakily slow our bikes down. or something.

Why am I even going down this road?

On my bike I’ve shown the exhaust side of the engine quite a lot of love and attention, but despite the nice, big-bore shiny pipesness, she continues to run better with a little baffle in the end, like so:

The best reason I can come up with that the bike runs better with a smaller diameter exit/baffle in the end (effectively restricting the flow again) is that perhaps the exhaust is a bit much pipe for the bike – and by that I mean for the amount of air the engine is moving, the pipe diameter gets too wide at the end, which ends up with the gasses slowing down too much and actually impeding scavenging of the exhaust system. Or maybe there’s some sort of sound-waves stuff going on like with two-strokes.

Either way with the baffle in you get a little bit of torque around that 70mph point where you shift into top gear. With the open pipe it didn’t have the oomph to push through that but with the baffle it does (albeit slowly).

A couple of months ago, under what turned out to be ideal conditions on a private runway, thanks to that baffle we hit 85mph.
That was on a 15t front gear too so would have needed even more torque to make it through to the power band.

And it was absolutely equal parts terrifying and exhilarating..,as you would expect flying along on a glorified moped! 😀

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