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Thread: Aftermarket exhaust vs. stock exhaust

  1. #1
    apriliaforum prov-nov
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    Angry Aftermarket exhaust vs. stock exhaust

    Last year I've derestricted stock exhaust on my RX50 (that is removed everything except cat inside expansion chamber) and in the next months I tried to more or less tune the carb. The problem with stock exhaust w/cat was that no matter how big main jet I throw in, it will never four stroke at WOT as it should, to give me some sign of over-richness to set jetting starting point. And plug reads were totally unusable with ceramic half brown-half deadly white (I would not rely just on plug reads anyway...) It did four stroke in mid-range however, so I found quite optimal setting with little larger atomiser 210GA (stock was 208). Still had cutting-out-fuel simptoms at WOT with A13 needle, changed to A20 (sharper tip, to let more fuel pass) and it was better, but it would still cut-out after time. I have never found cause for this...

    I gave up and ordered new exhaust, TurboKit R, with E-mark and homologation papers for RX50... It came with restrictor cone welded in two points, so I have grinded it out. 98-102 main jet and A20 needle is quite common configuration with stock cylinder/piped SX/RS/Derbi Sendas, so I didn't change anything in carb (MJ100/A20@#2/IJ32). This time I wanted to do it "by book" So: 1. warmed it up (not a problem, since it's 33 degrees outside ) - check, 2. set idle air mixture - check, 3. set main jet.. I accelerated but anything over 1/3 of throttle was just missfire and four-stroking... Top speed was 25kph! I wasn't sure If I left needle clip at 2nd notch from the top or bottom, so I checked in indeed it was wrongly positioned, so I've moved to #2 from top to lower needle. Now still four stroking, and when I progress it clears up a little, but still it won't go over 45kph...! New exhaust, but now I can't even reach WOT...!

    Is this needle problem (too sharp-to much tapper, should I try A13), way to big main jet (100) or both?

  2. #2
    apriliaforum prov-nov
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    Update: changed to A13 with middle clip, and now it is ridable, maybe still little rich and very underpowered under 6000rpm compared to stock exhaust, but when it reach 7500 it literally explodes and pulls all the way to 12000rpm. So exhaust definetely works, but is it normal that is so underpowered under 6000rpm..?

  3. #3
    apriliaforum expert Scoop's Avatar
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    I have the Yasuni, absolutely dead under 6000 rpm. I preferred my old stock unrestricted pipe but it was rusted to pieces and had to be replaced

  4. #4
    apriliaforum prov-nov
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    I had idea to fit back 14/53 gearing, which did stock pipe barely handle. I thought that it would be no problem for that extra power from that Turbo Kit pipe. But after testing with current 12/53 setup, I think i'd have to push bike at launch by myself, until it would reach 5000. Nightmare, if you are driving where are just traffic lights and cross roads...

  5. #5
    apriliaforum prov-nov
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    Today I did some extended riding, and you know what, it isn't that awfully powerless at low-range as I first thought, there is small 'bump' of power at 4000-5000 rpm, then there is completely flat spot at 6000 and then power band starts somewhere at 7000-7500... That's small 'bump' is just enough for very easy cruising, it feels just like totally restricted moped I did read about flat spots before entering power band, so I guess that's it...

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