Aprilia rs50 03 bogging under 6k

[Redheadsket]

So I need help with my 2 stroke rs50. She idles fine, starts first touch of the button and revs up normally but underload there's just no power and its just a slow build up through the rpm until I reach 6k and the bike turns into a rocket... well a 50cc rocket anyway. I can't figure out what's causing it to bog and I feel like I've gone through everything I can think of. She has had a full engine rebuild (Seals, bearings and top end) and service along with a few other things but they won't effect the running of the engine. I can't find any vacuum leaks and the engine is stock with no performance parts fitted and ran fine before the rebuild until the bearings went. I have a hunch it could be the cdi but they cost a lot to replace and I wanted to get some other opinions before I splash out. I feel like I'm being stupid and missing something so any help and advice would be appreciated. Thanks
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My 125 does 90mph in my dreams

[jeffyjeff]

Welcome, Redheadsket. Your description sounds more or less normal to me for a small displacement two stroke motorcycle; more specifically, one that has been tuned for maximum power output. During the top end rebuild, are you sure that the cylinder porting remained stock? The characteristics of these little engines are that they produce their power at higher rpms. If the power band starts at 6000 rpm, my recommendation is to ride your little 50cc rocket from 6000 rpm to redline all the time, every time you get on it.
PS. It's not your CDI
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History shows again and again how nature points out the folly of men - BOC

[Redheadsket]

Thanks for the reply and the welcome. One thing I forgot to mention is the bog makes it impossible to ride above 3rd gear as there is just not enough power. As soon as you shift up you can feel it slow down even at full throttle, I'm looking to sell the bike and its had a lot of work put into it and it would be a shame to sell it as not running properly. It feels like its fuel related but the reeds are fine and the jets are the same as I used before and the cylinder porting is definitely the same.
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My 125 does 90mph in my dreams

[stevo123]

Hi, I would double check carb, pay special attention to float height and needle position. Sounds like running rich lower down could be your problem. If the needle is high (ie clip lowered a notch) a richer mixture as medium throttle openings will be gained. Too rich and it will not burn and will bog down.
Sorry, went a bit TEF there...

[Riejufixing]

[Redheadsket]

Thanks for the suggestion I will check the needle position and float when I get a chance in the next few days. When I was rebuilding the engine I double checked everything along with my dad checking and I followed a Haynes manual just to make sure everything was done properly so I'm 99% sure everything went back together how it should. Ps. What I meant by a few other things that won't effect the running of the engine was a respray and brakes etc so hopefully a shiny coat of paint won't cause it to bog. Sorry for the confusion
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My 125 does 90mph in my dreams

[Riejufixing]

I was thinking about the piston. I don't know whether or not it's a directional fitting on these, if it is there should be the word "Front" or an arrow pointing towards the front.

[Redheadsket]

Oh yeah I know what ya mean it had a little arrow at the top of the piston and I remember double checking it when I put the piston on
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My 125 does 90mph in my dreams

[Easy-X]

Talking of pistons, how did you align the ring gaps? Blow-past would affect performance....
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Husqvarna Vitpilen 401, Yamaha XSR700, Honda Rebel, Yamaha DT175, Suzuki SV650 (loan) Fazer 600, Keeway Superlight 125, 50cc turd scooter