Tinkering with an '08 RS125

[Loud]

For those of you who don't feel like reading a back-story, my question is simply this:

Am I going to see much in the way of a performance gain by simply upgrading to a 34mm Carburettor on an otherwise stock engine?

For those with more time on their hands I'll try and make it worth your while to read on:

I'm a fan of Italian machinery and have been for 15 years. My friends think I'm laughable for this and, having had a lot of mileage with "Fix It Again Tony" jokes now take delight in pointing out that I have a glorified blowervac / lawnmower / chainsaw etc. To the stage where I can now arrive helmet-in-hand and be asked if I've been out doing the gardening...

For the most part I would consider myself a sensible person, it just so happens that I very occasionally find myself with both an idea and some money at the same time and a downright ridiculous decision often results. Such a time is now, partially thanks to a situation which has my friends laughing all the more...

My bike blew over.

Turns out that a cover acts as a sail and when you add an uneven grass surface (rookie, I know) it results in fairing damage. Fortunately for this ex-Financial Planner with a well-researched insurance policy (as well as mechanical and eBay skills) this may not cost me anything but time... and possibly a few friends if they keep this up.

Now to tie my ramblings in to my opening question.

I like improving things. Not that I want to turn this bike into something it's not designed to be but as a sensible person I upgraded the headlights to Phillips CrystalVisions (difference is like...night and day ) and less sensibly decided it 'needs' the tail tidy (despite the associated implications). I've done some questionable things like matching the jacket and helmet - although I reason that drivers will be impressed with my fashion sense and so are less likely to hit me - but also stooped as low as putting Marchesini stickers on the rims.

But should I touch the engine and will it make me feel better when I tell the next naive soul that it's not a 600 or even a 250?

I've read that the earlier bikes run the 34mm carburettor as they didn't need to comply with the later, stricter emissions requirements that necessitated the 28mm Dellorto on mine. So can I glue one of these on for an instant marginal hp increase or will the "poor thing drown" as a vintage GS1000 rider put it (after failing to keep up with me around a few corners)? Should I go ahead would much head-work be required to get a worthwhile result and, if so, is a dentist going to be more useful than a mechanic? I’d rather leave all else as it is, at least until it’s first major rebuild in another 7,000km. Apart from maybe some tent-pegs to keep it parked upright...

Thoughts?

[MattyA]

vaccume cleaner motor supercharger.

[Mikeymikemike]

they may be quick and nimble around slower corners, but you will get eaten up elsewhere, so if youre after performance gain, sell the bike and buy another italian beast they can be just as quick and fun around tight corners in the right hands.

[Loud]

they may be quick and nimble around slower corners, but you will get eaten up elsewhere, so if youre after performance gain, sell the bike and buy another italian beast they can be just as quick and fun around tight corners in the right hands.

Okay so my question was about the merits of upgrading my carburettor and this reply tells me that I should dispose of my apparently slow bike (that I think is great) and buy a bigger bike that I'm not licensed to ride for at least 10 months...? Dude is that a 'Loose' Cannon pictured in your Avatar?

I'll tell you what, I'll find a performance figure from the R123 motor (I believe this is the pre-emission controlled version of the R122 motor apparently fitted to my bike) which has the 34mm carb and matched head. This should give me an idea of the performance increase I'm likely to see unless anyone can provide some insight. For me to then make a judgement call on whether or not to go ahead could someone suggest a good place to contact about the headwork and tuning?

[darkfibre]

Interesting feedback so far.

What you really need to do is research the difference between the R122 and R123 engines.
If there is porting, exhaust and advance changes to match the carb difference, then I would say dont change to the larger carb. A larger carb is normally only a good choice if the original is restrictive.

If you can find out all the changes between the engines, then change everything required to match the higher powered engine.
Miss match of components with no tuning experience is to be avoided.

[Jamathi]

If engine tune(porting etc) is set up for 28mm then putting a bigger carbie on it will make it a lot less flexable.
This will be very noticable in lower revs where the airspeed will be to slow to mix the correct airfuel mixture (hole of Carbie to big)
This will mean trashing it to keep it going, clutching everywhere and always in highrev range.
This will become very anoying very soon and expensive!
From what i know of these particular bikes is that they are already very highly tunesd for road riding.
Enjoy it as it is would be my useless advise!

[speed3]

Firstly. F$%# the haters, you have an awesome little bike there that is as fun as or more than any big bore. Never sell it.

On topic, I think you should go all out on it and do the pipe, carby, porting and anything else you can think of. The original had a 34mm so you know straight away that the motor is designed for that amount of fuel/air flow. Also have you done the de-restriction mod or whatever it is?

[Rich...]

I know these were originally designed for the CBR125, but I'm sure Robbo Industries could convert one to suit your bike...



As Mr Speed3 has mentioned...do the lot...make it a matched set...

[BigTim]

PM Stratos, and ask him to weigh in to this thread. He's a pretty full bottle on what's available for the RS125s.
He may still have a few tasty parts laying around for one.

[M|ke]

I know these were originally designed for the CBR125, but I'm sure Robbo Industries could convert one to suit your bike...



As Mr Speed3 has mentioned...do the lot...make it a matched set...

Exactly what I thought of when I first seen this thread

[Loud]

Some very helpful advice amongst the replies, thank you.

A little research on the R123 and R122 engines indicates that port work and CDI changes may be required, meaning that the carburettor won't happen until at least the 15,000 km major rebuild.

I'm not interested in sinking $$$ into modifications, it was simply a case that at $250 a 34mm carburettor seemed like an opportunity for cheap power - in DOHC Fiats a carb upgrade can yield 20% on factory output with no other changes but it appears this won't be the case for the RS.

As for the blower vac kit, piss off - that's a 4 stroke Ryobi unit, I might as well get a Ninja...

[PaulMac]

Mate, no experience with 2 stroke 125cc road bikes but if I saw a 28mm carb on any of my 125cc 2 stroke motocross bikes, you'd be looking at the back of the pack to find it in a race. The smaller carb will give you better throttle response and more power from idle to mid but the engine will struggle to breath up top. Just waht learners need. You probably could toss just the 34mm carb on and nothing else and you would find a noticeable improvement up high in revs along with a corresponding loss down low in the revs. I'd also imagine you'd need a few jets to get it to carburate properly with the porting you have. If it was my bike and my money, I'd get the 34mm carb, race expansion chamber/ silencer and buy an earlier model cylinder from the wreckers or get the earlier port specs and get your cylinder ported to match. Pipe, porting and carb work is all most two strokes need to unleash the full potential.

[Gangus]

yours is a rotax engine right? A decent 2 stroke. It will benifit from a larger carb as you dont use the motor for torque at low rpm. Scour the wreckers over east as a pre set up carb will be dynamite compared to ginning about preping a carb from scratch. good luck!

[Mikeymikemike]

haha, your bike is by no means slow and it is great!

[Loud]

Found a very useful UK site with parts to suit the RS125 - including 34mm Dellortos pre-set for post '06 bikes in stock trim.

P J Motorcycle Engineers LTD Aprilia RS125 Air Filter/ Fuel/ Carburettor

[Lukey]

^^^ awesome site thanks!
ive just recently traded my 09 ninja for an 09 rs 125. need i say why... anyway, sorry to bump this topic, but Jesse M have you done any mods to your rs?

[Mr DJ]

That's a very nice bike you have there mate. I trust you are taking very good care of it.

[Loud]

Thanks Mr DJ, I bought it from a very caring owner I've racked up 4000km these past 3 months too!

No mechanical mods Lukey, I had it serviced at 9000km and it transformed the bike - although it's playing up again at the moment... bloody Italians! After listening to the advice above I don't know that I will either - I haven't found swap-in CDI to take advantage of mods anyway.

[Lukey]

errrh wats wrong with it?
apparently the aust. imports are full power and dont need the cdi mod according to my dealer?! an exhuast and jet will be enough.. do you concour?
ive only recently put 1000kms on the clock and had it serviced, hence why im looking at an exhaust....

[db7gtgrigio]

I have an 08 RS125 as well as an 02 RS250 and a 1974 Ducati. The 125 is a wonderful bike and certainly fast enough to have great fun. I have taken it to eastern Creek in the medium group and while EVERYTHING overtakes you on the main straight it is great fun getting them under brakes into turn 2. Turn 1 is taken flat out 160km/h chin on the tank stock std bike.
the 125 has 33hp form 125cc or 264hp per litre. The RS 250 has 60 hp from 250cc or 240bhp per litre. My frined r1 has about 170hp per litre. So the 125 is pretty highly tuned already. And yes I belive all Aus RS125s are full power. The European ones now have cat converters which I don't think ours do.
My 65 yr old father came for a ride with me last week. he took the 125, I took the 250. He normally rides a (shhhh) harley. he loved the 125 thought. said it reminded him of his youth and that while it was quite peaky he reckoned it was faster than his 500cc triumph daytona.

I would not bother tuning it. It is super tuned already and all the research I did on the web siad you will lose any mid range and sacrifice engine reliability. ust enjoy it for what it is - great fun.