Mild 50cc Liquid Cooled 103

by Andrew Scouten
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This was my first go at a 103, it went through a few variations before winding up where it is now. For my first build I used the cheapo 90$ 6 port 50cc Airsal with an Teknix high comp head, Polini Country exhaust, same everything else, the bike did pretty decent, hitting 43 on stock gearing, not bad, however I dropped the pipe while riding, ran it over, stripped the exhaust threads. So I tried out a 50cc Gila, fuccckkkk that cylinder, its 160$, the port timing is shit, the ports are crap, it did like 35 out of the box, ya ya ya you can port it, and I eventually did, which got it to 45, however, that Airsal out of the box was a MUCH better cylinder. I modded the stock variator, 3 balls, 2 star washers, 2 m6 nuts on each variator arm, and the bike moves pretty good off the line with my large self on it. but then....a Treats sale happened, there was a 50cc full LC Airsal kit for sale....105$. Needless to say I bought it, now this version did not have the porting of the 6-port 50 Airsal, it was actually a re-pop of the late model stock cylinders, so I opened the exhaust port up, enlarged the transfers to match the case, and it was decent! 43mph on stock gearing, but with better torque then the previous set up, likely due to the lower temps allowing for substantially better jetting. For the Liquid cooling I decided a pump was really unneeded, thermosyphon would do the trick, my temps run around 220-280 and Im good with that. Next I re-geared the bike for a bit more top end, getting to 47 with out really losing any bottom end, a happy medium that leaves us where the bike is today, rally ready. Edit: I could not stand the shitty bottom end, went back to 11x56, it did like 38 forever and it was quick…. I built a few more fast 103’s after this, but I kept staring at this thing. Time for a re-visit, added a Doppler, 19phbg, er3/clutch pulley, and a pump powered by a regulator/rectifier with battery in-line. Now it rips off the line, and does 48


1978 Peugeot 103SP




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