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Thread: RS250 Aprilia Horsepower issues ETC

  1. #1
    apriliaforum newb
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    Angry RS250 Aprilia Horsepower issues ETC

    Hi all, After a little help and guidence etc on what the common horsepower outputs should be with the following mods etc. This is where Im at.

    I bought the rs around 2 months ago, have done 2 test days, and 3 race days, coming home with a much suprising 3rd place overall on my last race event in the Pre 96 f3 class we have.

    My big issue was the straight, every bike I was up against, whether it be rgvs tzrs or other rs's just destroyed me down the straight even if I shifted the same and carried more corner speed onto the straight. I had the opportunity to throw it on the dyno so today I did so to see whether I was down on power or just needed to shift earlier etc.

    It came out at 53.7 Horsepower. Which to me is a very underpowered bike, as when i bought it i was told it was dynoed at 64. I have done 5 hours tops on bike since owning it, it and it had been freshly rebuilt 4 hours previous to me buying it. Came with all receipts etc and the guy is very trustworthy although he could not supply dyno sheets etc. It was rebuilt by a well known 2stroker in New zealand.

    It has tyga pipes, and been tuned, running BR9ECM plugs, running on what we call 98 octane pump gas. Single ring vertex pistons (minimum size) i think .94. I am still running factory squish to my knowledge. and I dont think the heads have been O ringed. Still factory head gasket and base gaskets etc. Using castrol TTX Oil.

    I already have some new pistons to put in, another set of the same vertex single ring from tuning works. Got the same size as whats in it.


    I have left the bike with the shop and will give them the pistons to swap for me, I was planning on doing it myself, but I thought since they have a good name and there could be issues, I thought it would be better to give it to them, to do the pistons and run up and retune on dyno.

    My big question is, with these mods, what horsepower should I be looking for on the dyno ? I understand there could be up to 10% variations between dynos etc. but at the moment it seems very underpowered. My gut says its either down on compression or the powervalves arent quite right, Ever since I have had the bike, it has stuttered entering powerband. If i am out of powerband in 3rd or 4th etc, It will stutter for at least 5 seconds if not more before it enteres powerband and pulls away. This is the same in 2nd but not quite as bad. I try not to let the bike stutter by just flicking the clutch to get it into powerzone, and once I have done so it seems ok. I have nothing to compare this to as its the first two stroke ive ever owned or ridden. The band is also shorter than I expect, looking at videos of other racers im racing with, they seem to have a wider powerband. All the other bikes are destroying me down the straight even if Im drafting them.

    Without doing any more mods, just running properly. What should I expect to see ?

    Thanks in advance to all.

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  2. #2
    apriliaforum Junkie gangus's Avatar
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    60hp with fresh pistons. Getting heads squished/ updated shape will give you another 4.
    Post up in the rs250 section

  3. #3
    apriliaforum Junkie gsaltus's Avatar
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    Your bike is basically stock with pipes. Your right the range where the bike should be. If you want a quick fix you should play with the jetting and run a mix of Pump and Race fuel. Race gas will give you a good bump in HP but you shouldn't run full fuel until you change the heads. VP Fuel C11 or C12

    Gone but not forgotten.

  4. #4
    apriliaforum expert mattology's Avatar
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    not every dyno reads the very same, so i can tell you that one dyno may read 60 and another may read 65 so it's hard to say, but if you're going through a full rebuild look into the following:

    new 3 piece billet powervalves
    new billet cylinder heads with inserts for avgas
    zeeltronic programmable ecu

    if you do that along with the rest of the stuff you already have, and you set the squish properly, you will enjoy the power the bike is able to make.

    turning more rpm will make more power, but just make sure your crank is healthy, and you'll be happy with it.

    Make sure your power jets and air solenoids are working properly also.. if its too rich up top it wont rev out
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