2 stroke maintenance and tuning - RS125

[c_dug]

Hi All,

I own a relatively rare Tuono 125 2 stroke, it looks a bit like this one:
https://2.bp.blogspot.com/-CKiGV4OMp24/Uaxl8Vo2tfI/AAAAAAAACRk/sG2_tte8vVw/s1600/Malaysia-Aprilia+Tuno+silver.jpg

It's essentially an RS125, with a different fairing and bars.

I originally bought it for my other half to learn on, but I've since realised how rare they are, and also quite enjoyed riding it, so, it's mine now

It runs okay at the moment, but I'm aware that its due a top end rebuild around about now. It also bounces hard off the rev limiter at 80mph in top gear, which would suggest it's probably been at least partially derestricted at some point, a cursory glance would suggest the front sprocket has dropped a size or two too.

I know these are capable of outputting high 20s bhp, low 30s at a push, and I'd like to get it towards those figures. I can work a set of tools, but I don't really have the knowledge of tuning two strokes, and I'd rather not learn the expensive way when it can be avoided!

As far as I'm aware, it's virtually standard at the moment. Where do I start?

Sporty barrel?
Bigger carb?
K&N filter?
Sporty pipe?

How do I work out jetting for the above?

I'm not intent on keeping it bog standard to eek every penny out of it's value in 15 years time, I'd rather enjoy hooning around on it now, and showing it off down the ace (It gets about as much attention as my old TDR250 did!).

All advice appreciated,

Thanks!
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I am a bellend, I am a man of constant sorrow, I am a gummy bear, I am a rock.

[Robby]

My memories of people doing 2-stroke tuning on their 125s back in the day mostly ended up with people messing with their bikes to try to make them as quick as an RS125. This generally failed. They seem a lot more sensitive to fuel/air mixture than 4 strokes, and you have to get the oil mixture right as well.

That said, the usual best and safest (for the engine) bolt-on power is in the exhaust. 2-strokes make their power on the clever maths happening in the expansion chamber.

You're a grown-up, with experience of big bikes. Rebuild and service that one, then see how it rides. Once that is done, decide if you want to sink a lot of cash into it for 2 more bhp.

[redeem ouzzer]

Decent pipe, bigger carb (ideally one that lets you use the air box, if not then run it open, programmable ignition.

Then dyno time...
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Be a REAL MAN!

[RhynoCZ]

I was gonna say keep it stock, that it's not worth the money and worse MPG with short service intervals..., but then I'd like to see you fitting a RS 125 engine with big bore kit in it.
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'87 Honda XBR 500, '96 Kawasaki ZX7R P1, '90 Honda CB-1, '88 Kawasaki GPz550, MZ 150 ETZ
'95 Mercedes-Benz w202 C200 CGI, '98 Mercedes-Benz w210 E200 Kompressor

[stevo as b4]

[c_dug]

It's never going to be an every day bike, but I'm not chasing every last bhp at the cost of worrying it'll go pop either. I'd rather it ran reliably at 30bhp than unreliably at 35! I'd quite like a shiny stainless spanny, just because I'm a tart.

I guess step one as suggested, is get it running properly in pretty standard condition, and go from there.

Does anybody know how to tell whether my expansion chamber contains the restriction bits and bobs, or whether it was full power from the factory?
____________________
I am a bellend, I am a man of constant sorrow, I am a gummy bear, I am a rock.

[Kickstart]

Hi

It isn't so much the pipes were restricted, rather than they landed up with all sorts of rubbish in them as time went on to get through noise and emissions tests. Early bikes had better pipes, and with later ones potentially quite a bit of power from a decent pipe.

After that, later carb, played with barrel, played with cdi unit if you want.

All the best

Katy
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[c_dug]

Is it worth opening up and gutting the oem pipe initially, or am I better off spending some pennies on a JL pipe or something of the like?
____________________
I am a bellend, I am a man of constant sorrow, I am a gummy bear, I am a rock.

[Kickstart]

Hi

Honestly not sure. Personally tart value (and not liking to do things that can't be undone) would make me buy a new one

All the best

Katy
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[ScottT]

Polish the ports, then split the engine and make sure your transfer ports line up with the crankcase, and theres no gasket in the way.
Then start blueprinting the engine, get everything 100% right, that alone will give some increase and give you a baseline to start from, you have no idea what has been fiddled with by previous owner.

Do a google search someone once used the rs50 engine for a landspeed record bike, reading what they did will give you plenty of ideas what can be done with a small 2 stroke engine.

[Kickstart]

[stevo as b4]

Fucking lol!

Polishing ports, which ones? How shiny should they be? What are you doing to stop the fuel from clinging to the shiny port walls?

I don't know how many two stroke bike engines Scotty has tuned or stripped, but do you really think on all relatively modern two strokes, that there are huge casting obstructions in the transfer ducting and where the liners meet the crankcase?

Also everything you have said even if there was some some small casting imperfections and mismatch between gaskets and port entry areas, is very minor in restriction to air flow. The manufacturers would get it perfect if they were losing any noticeable or easy to get at bhp.

So best case scenario is that your so called blue printing is going to gain a few fractions not masses of power. Tuners don't generally go for the tiny time consuming details if there's much more noticeable and dramatic gains available elsewhere.

[ScottT]