Tag Archives: r125-general-tuning

Racing

RWYB at Dakota, 16th August

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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, Blog, DIY-Dyno, Racing

The becoming of a drag queen?

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So I went to check out a disused airfield nearby (in the header) with a view to doing some sort of top speed run, as legally as possible, on level ground.

And whilst it’s a great moody spot (especially in the mist) and it might work for head-to-head over an 1/8 mile or something like that, unfortunately it wasn’t really smooth enough to even be thinking about trying to get near triple digits like i’d been hoping to.

Which sucks, I was really hoping it would be suitable as santa pod is such a looong way away.

Well, dismayed I went back to check out if any other options had magically presented themselves, and in fact they had!

Last year I booked in to an event at Dakota Raceway which was then cancelled at short notice, and given they’d cancelled all events for the rest of the year after that, I thought it was game over there.

But apparently they’re back, which is awesome. and they have a RWYB event on the 16th August….so….

BOOKED!

Unfortunately it’s also only 1/8mile rather than 1/4, so we still won’t be hitting top speeds and will need to gear right down, and it’s likely to be as rough as the other airstrip, but it’s organised racing with (presumably) proper timing gear and any racing is fun so hell tf yes. Plus I bet they have an ambulance on standby which is a lot more than we’d have out in the wilderness by ourselves.

No-prep, not no prep:

So given I’ve been kinda flat out with moving the last couple of years, i’ve not really done a whole lot to the bike. I was very lucky in that I was able to just build the current engine, put it in and it *relentlessly*worked*great* for a couple of years, despite much adverse weather and circumstance. Nonetheless, I still wanted to give her an at least cursory going over to check there weren’t any glaringly obvious issues pending which might escalate when being run repeatedly down some rough concrete. I also wanted to just listen and feel and check that what I’d been observing while out riding was actually grounded in reality.

Dyno time

Whilst my dyno still doesn’t really give reliable power readings (yet!), so i can’t really say “it has x hp” with any certainty (at all), it does let me observe the bike closely while it’s under load, which is something I don’t usually get to do (e.g. when riding).

Whilst I’ve been working on the 2019/gen3 i’ve been kinda spoilt since the Tuneboss ECU works over bluetooth so I was able to keep my phone connected the whole time and either watch the map or be datalogging or whatever the whole time – it’s been rather convenient.

However, this bike is built using “prev-gen” technology so it’s all laptops and USB cables to talk to the PCV, flashing ecus (very slowly) with a spaghetti of wires and a half-hour round-trip to make a single change (and risk bricking your ECU)..arg. I’m realising how easy i’ve had it on the gen3 xD.

Since i can’t fit a laptop on the fuel tank, I also can’t usually have the PCV software hooked up when it’s in gear and under load so being able to see the AFR values and just generally how it’s doing whilst feeding it different throttle situations, is pretty useful (again, on the gen3 the AFR gauge on the dash let’s me keep an eye on that while riding).

I’m sure I’ll figure the dyno thing (not being able to get truly comparable/repeatable results) out in due course, and in fact i have thoughts on this so I’m trying to not be too annoyed that it hasn’t worked perfectly like I expected right out of the gate, but instead am trying to use the roller in ways I *can* apply and are still helpful… like being able to see what the bike does at 60mph.

Power readings or not, that’s still incredibly useful from a diagnostic perspective. Imagine being able to observe, prod and poke your bike while it’s at speed and hooked up to monitoring gear? Very handy.

I had a few modifications planned for the bike and was hoping to get them done before Dakota but actually my takeaway from today’s session is “it’s great! don’t mess with it, go race”, so I’m going to do just that and give myself a break for once.

Forced modifications, vibrational harmonization:

The modifications mentioned above are neither whimsical nor through choice.

Continue reading The becoming of a drag queen? →
B-motor, Yamaha YZF-R125

YZF R125 180cc kit top speed

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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.

Continue reading YZF R125 180cc kit top speed →
Yamaha YZF-R125

Autotune – game changer

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(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 wordpress.com 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 →
Yamaha YZF-R125

Fitting an extra temperature gauge to the YZF-R125

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[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 →
Yamaha YZF-R125

Baffled again..Exhaust tuning with custom baffle

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My account on r125forum.com 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 →
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Manual timing chain tensioner on YZF-R125

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More fun with taking engines apart and finding things not as they should be on the YZF-R125

Yamaha YZF-R125

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

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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! 😀

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

Changing front sprocket on yamaha yzf-r125

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This is me trying to do a walkthrough of changing the front/drive sprocket on a Yamaha YZF-R125 without a rear wheel stand/paddock stand.

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Yamaha YZF-R125

Baffled – Part 3

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So I found this thread which possibly explains what’s going on with my exhaust (2nd post particularly relevant).

i think this may be about gas velocity, which would sorta explain the current counter-intuitive performance improvement by adding the baffle in the can. I’ve also realised that it might be better still if i take the forward baffle out (the one which came with the exhaust system) and only have the rear one…that way i might get better performance still and regain some of the nice sound.

It may also do nothing/make it slower in which case it’s going back how it was….gonna find out today hopefully.

Continue reading Baffled – Part 3 →