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maxemillione
11-03-2015, 03:50 PM
Hi, I'm a new member here and need help with a carburetor.
My daughter has just bought a 2009 rs50 which I promised to fix up for her which I have succesfully done, but am a little stuck with the carb (2 strokes are not my forte)
The bike as bought has 80cc big bore kit, de-restricted exhaust, carbon fibre reeds, more or less straight through air filter and a chinese (mikuni copy I think) what appears to be a 25mm carb.
As it stands, I can get the bike to start ok and rev out from 4000rpm, but flat as a pancake from 1000 to 4000.
I'm guessing I need bigger jets, can anyone advise me which jets might be a good place to start with or should the carb be changed ?
Any help would be very much appreciated.
Thanks

Spudgun60
11-03-2015, 04:08 PM
Hi and welcome aboard. This really ought to be in the Technical section, but no matter.

In my view. The engine being 'flat as a pancake' from 1000 to 4000rpm is perfectly normal. Hell. My engine idles at 1750rpm. Having such a small capacity. These engines need to be thrashed without mercy to get anywhere. I don't get anything resembling power until I reach 6000rpm. I spend a lot of time at 10,000rpm.

maxemillione
11-03-2015, 06:12 PM
Thanks Spudgun,
When I say flat, she would have to blip the throttle like mad just to pull away from the lights, nothing smooth there, open the throttle and it just blurps and wants to stall unless you blip away at it maybe 6 or 7 times.
Power isn't really the issue for us, all I want is for her to be able to pull away smoothly and be able to reach a safe 50mph on the country roads, no way was I letting her onto a busy A road only being able to do 30mph, far too dangerous.
I've got my mind on upping the jets, but haven't a clue where to start, would love some advice from someone who has sorted this problem before !

ToraTora
11-04-2015, 12:10 AM
Hi Max,

Lots of info on this in the technical section (http://www.apriliaforum.com/forums/forumdisplay.php?21-RS50-Technical). You'll also get more eyeballs on your posts. This section is for describing a project build. :)

When looking for stuff for your bike look for Derbi engines. The bike you have has a Derbi Euro3 engine, but it's very similar to the Euro2 engine. The older bikes employed a Minirelli AM6. Very different than what's in your bike, and will confuse the hell out of you if you listen to folks talk about the AM6--which they are most likely to do when you say RS50.

Spudgun60
11-04-2015, 11:58 AM
Thanks Spudgun,
When I say flat, she would have to blip the throttle like mad just to pull away from the lights, nothing smooth there, open the throttle and it just blurps and wants to stall unless you blip away at it maybe 6 or 7 times.

Ahhhh. I understand now. You have (What many would call) a 'flat spot'. You've got it in the most awkward position as well. In truth. I've never had a 2-stroke with a flat spot, so I can't give you a 2-stroke answer. I've had flat spots on 4-strokes though. My Enfield had a flat spot in exactly the same place. The was cured by fitting a richer slide. That's a slide with a larger cutaway.

You've said that your carb appears to be a Mikuni copy. If so. Mikuni and Mikcarb (A Licenced copy as fitted to Enfields) will fit. I know that different slides are available for the Mikcarb (because I fitted one), so you should be OK for parts.

However. It would be useful if you Posted a picture of your carb. So it can be positively identified.