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…
ok so we’re about 1200miles down on the rebuilt B-motor with rebalanced internals and right the way through break-in miles I felt like the clutch was slipping. I sorta expected this because on the previous motor it slipped from too much power so didn’t really think much of it. Every now and then it did seem to “catch” properly and would dig in and take off but it seemed to be random. For those times it happened though.. wow.
But then at the end of break-in miles since i had to change the oil anyway I put the upgraded clutch (R15 clutch basket with 6-spring boss + uprated springs) from the old engine and it still wasn’t quite hitting the speeds I was expecting. It would get to about 85mph but not any further and given this engine has the power band back in the correct place and screams from about 8.5k right thru the limiter this was unexpected behaviour.
I had been expecting the map to take a while to adapt to the new engine but really it ought to have done that by now. I had recently done a 2hrs each way run which was all main roads so we were in the 8-10.5k range most of that run which meant the autotune had plenty of time to do its thing and sort the map.
The other week I thought I’d just try it on the 14t front sprocket as a test and weirdly it was still not catching right…so I dug into it a bit more and discovered I’d put the clutch cable in a different position from how i’d had it before to see if i could lighten the pull, and then forgot I’d done that. It’s a 1 finger stunt clutch with 3 cable positions so you can vary the travel/pull-weight and as it turns out in the “lightest” position where I had it (which gives the least clutch movement) it was never fully engaging the clutch….
So then I switched it back to the middle position back to the somewhat heavier pull and holy chickenballs what an instant difference.
Continue reading B-motor – 1200mile updateSince the “A-motor” has been removed from the bike now, I need to strip the upgraded clutch I built a while back off it, since the newly rebuilt “B-motor” is already slipping on the stock clutch and the upgraded one needs transferring to that engine when I do the “end of break-in miles” oil change.
Continue reading YZF-R125 R15 Clutch upgrade – 6000 miles inspection and stock clutch install speedrunwoop! it runs \o/ (so far).
This has been a massive learning curve for me, particularly the sheer number of operations which have to be completed, as well as having to build at least 2 special tools to get the job done meant (for me anyway) it wasn’t really possible to “see” the whole process from start to finish, which in turn makes me very nervous on a project.
Continue reading The B-motor runs!!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.
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 speedI started a thread on the forums a little while ago but meant to mirror it here. I may add in the old posts here if i get time but otherwise this will have to serve as a little photo-catchup. please refer to the forum thread for the full story. I’ll try and update both moving forwards..
Whilst not pictured here the cylinder and head are loosely on now while I set up the timing chain etc. Hopefully in the next few days it should be ready to fit.
[EDIT: pics updated, engine fitted and runs!]
Biting the bullet here and using the ebay hydraulic pless to separate the halves of the crankshaft and replace the con-rod etc. This is getting serious now..
going further down the crankshaft-rebuild rabbit-hole and getting on with the crankshaft rebuild for my new motor…
In this video we’re looking at trying to calculate the balance factor for the old 125cc setup vs with the big-bore kit, to see if that maybe explains why it’s run a little differently since going big-bore.
The logic is based on this video from 2StrokeStuffing (thank you!): https://www.youtube.com/watch?v=0hoE_…
B-motor crankshaft rebuild progress in pictures…
what we’re starting with..
This is me attempting to replace the inner camshaft bearing on a YZF-R125 cylinder head.
I’ve not done this process before and it involves extracting a bearing from a blind hole. I’ve found how it’s meant to be done but this is a test to see how well that goes to see how difficult it is, and to help me decide whether it’s something I want to try doing on my main engine.
The bearing puller I’m using is pretty much the default ebay one, just search on “blind bearing puller”.
