Tag Archives: YZF-R125 modified

B-motor – 1200mile update

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

The B-motor runs!!

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!!

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

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!]

Splitting the crankshaft on YZF-R125

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..

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).