I’ve been a long time owner of a Gilera Runner 180SP which has loads of punch and been great fun to ride, but hey, it’s 172cc and it performs like a 2 stroke should.
But I felt I needed something else in the stable.
I’ve recently bought a new Aprilia SR50 Biaggi SBK replica, and to be honest, was a little underwhelmed with it’s performance.
Okay, yeah I know it’s “only” a 50cc”and I shouldn’t expect too much from it, but my wife’s LX50 Vespa had more get up and go.
These Aprilias get rave reviews in Pommie land for performance, top speed and handling.
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Time to uncork it, me thinks….
I opened up the transmission, took the restrictor washer from the CVT variator, put 5.5gm rollers in instead of stock 6.5gm and buttoned it back again.
I also cleaned the carb, airbox and checked for any other restrictors. None found.
Result? Well, not a great deal of difference with acceleration really, still gutless up hills but top end was okay on flats, and it was better downhill, indicating 75kmph on clock no worries.
Time for more research in go fasting…
So after some hours reading performance forums, checking out any other factory restrictions in carb, airbox or stock exhaust, I came to the conclusion that the catalyzed stock exhaust was the main issue.
I got online and purchased a Leo Vince TT exhaust on Ebay, some stiffer clutch springs and slightly lighter rollers again, this time 4.8gm, all of which came with pipe. I also bought a jetting kit to set pipe up properly, as a lot of peeps seem to have issues with the right jet selection.
2 days before Xmas, a nice box arrived from Italy, so I finally got a chance for some workshop time on Boxing Day and installed the pipe.
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Opened up the carb again and Fuck me, it had a stock 53 main jet.WTF? That's tiny, she said. I thought these things run a 57 main jet.
No wonder the poor thing was struggling the whole time, not enough go-juice getting through.
Economical, yes, but to the detriment of any performance. Out that goes, and in with the new, I upjetted to a size 62 main.
After my initial test ride, I think this jet is probably about the right size, although some people do recommend running up to size 70 main jet. I’ll do a plug chop after a few more km’s and see if it’s running lean or not.
I left the airbox stock (recommended) but blanked off the Secondary Air System (Piaggio engine) as it only recirculates exhaust gases (required in Europe due to 2-stroke emissions laws) and is not really required with performance exhausts.
I hit the starter and gave it a few squirts on the throttle, it sounded crisp right off the mark and had good throttle response through the rev range. Time for a road test, under rider load so to speak.
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Christ on a bike! What a different machine! It just took off from the get go, and once the scoot hits mid rev range, it really kicks into performance mode.
No worries at all reaching 75 kmph on the flats and just keeps pulling past the clock stops at 80 kmph.
I’m gonna have to GPS the top speed because my speedo doesn’t read higher than 80, or 50 mph.
I’d guess it was topping out at 95-100 + because I was catching up to cars on the highway.
Came back home grinning like a schoolboy who’d just got his first root.
Happy? Fuck yes. I just hope it doesn’t go and hand grenade on me. If it does, time for a 70cc kit
So, anyone else had good performance results from their ‘ped?
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Originally Posted by CrazyFrog
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