Tag Archives: B-motor

Racing, Yamaha YZF-R125

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

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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).

———

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

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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, Yamaha YZF-R125

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

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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…

B-motor, Yamaha YZF-R125

B-motor – 1200mile update

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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 update →
B-motor, Yamaha YZF-R125

The B-motor runs!!

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woop! 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!! →
B-motor, Yamaha YZF-R125

YZF-R125 180cc “B-motor” engine build photo catchup

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I 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!]

casing halves possibly with new bearings
the tool I made to pull the crank into position worked perfectly
oem piston
180cc piston

Yamaha YZF-R125

Splitting the crankshaft on YZF-R125

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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..

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Finding crankshaft balance factor on YZF-R125

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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, Yamaha YZF-R125

splitting the B-Motor crankshaft on YZF-R125

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B-motor crankshaft rebuild progress in pictures…

what we’re starting with..

Continue reading splitting the B-Motor crankshaft on YZF-R125 →
Yamaha YZF-R125

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

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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…