Tag Archives: r125-general-tuning

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

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

Changing front sprocket on yamaha yzf-r125

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.

Continue reading Changing front sprocket on yamaha yzf-r125

Baffled – Part 3

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

Baffled – Part 2

I did another quick run across town just now with the baffle in and it definitely seems quicker. I dunno if that’s because I’m less conscious of the rpm and so ride differently but it definitely felt like it wanted to *go* again. Much grinning when I got home. 

I guess it’s possible that at low/mid rpm the little bit of restriction might improve torque somehow – I guess there’s sound waves and stuff going on in there to some extent like a 2-stroke. I didn’t really get chance to go flat out though and that’s where I’d expect the baffle to be a restriction…will have to see. Didn’t seem to be a problem revving high at speeds up to 50ish though, kept finding i had to back off a bit.

I’m still not loving the sound but stealth is better and obviously whatever’s quicker wins. Interested to see how it does on a test run. I guess I need to figure out some sort of timing malarkey I can work with gloves on first, though even just seeing how it performs when flat out with the baffle would be interesting. Next time she’s on the dyno I guess we’ll find out for sure but that won’t be for a while yet.

Baffled!

I did a little test run today, primarily wanting to put some miles on the new tyres…unexpected results in other areas tho.

A couple of months ago when I got the PCV fitted and bike tuned I also got them to put a 15t sprocket on the front since I’d kept bouncing off the gearing up until then and was looking for better cruising rpm (e.g. so I can cruise at 70ish over longer distances without revving like a twat the whole way). which is fine, but it meant I’d never had a direct comparison with before/after tune on the original gearing.

In the spirit of seeing just how good my “mud and snow” rated winter tyres are, I’m wanting to do some “local exploring” where I’d likely be wanting acceleration over top end so I put the 14t back on to test. Also for exploring a degree of stealth may be beneficial so I put the baffle in the end of the can (which I’ve also never tested properly). Without the baffle “stealthy” is definitely not a quality it has.

Continue reading Baffled!