Tag Archives: YZF-R125 exhaust over-scavenging

Baffled again..Exhaust tuning with custom baffle

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.

Either way I had it tapered side out and performance was great but horrible clacky, farty sound. Just tested it the other way around today (flat side out) and performance is even better and sound much improved and pretty much perfect. You can go really quiet if you need to stay low profile, but when on it properly she makes all the right noises. Not as many pops and bangs as de-baffled but enough 😉

so just been out for a wicked test ride today – ~30 mins each way, country roads, town and fast 3-lane a-roads too, and she absolutely aced the lot. A-roads are now actually kinda fun. Keeping up with traffic wasn’t a problem at all and she pulled 82 into a strong wind before running out of road again, and that was with a large, flat protruding rucksack on me too, and with the motox bars and cut down screen which are a real hit to the aero.

On standard clipons, without the cut-down screen, without the backpack/sail and in full tuck I reckon 85mph and beyond would be actually fine, and probably pretty terrifying B-)

We weren’t out of revs either – obviously I was focussed on where I was going but I think we were around 9k so plenty more headroom and she was bang in the the “surge”/torque, which seems to come in around 7k and last till just shy of 10k since the new baffle. She definitely pulled all the way to 10.5 one time too so it doesn’t seem to drop off now like it did before.

It’s hard to explain just how happy I am about how she rides now. It’s like running with an excited puppy. Still a puppy but hella fun and up for anything. Keeping up with traffic on an a-road wasn’t a problem, I actually quite enjoyed the fast section, wouldn’t mind a bit more of that. A showdown with literally any bigger bike will not go my way but so what lol.

I need to set up an alternate map since atm I’m just on the one from the wideband, and I thnk the 0% throttle might need to be a bit leaner (big of bogging when you crack the throttle) and i’d like an alternative fuelling (e.g. +/- 10%) for flat out too and see if anything changes there esp now with what’s probably over-scavenging aka “the surge”. The top end could still be a bit stronger but I think the piston is also still loosening up to higher rpm so not looking to rush it, and given we haven’t changed the throttle body, intake or valves I reckon she’s doing bloody amazing \o/