First build, Stihl FS 48 trimmer engine

[Buzzerbiker]

This is my Stihl 23cc buzzer bike. Have been contemplating such an animal a while. I've purchased several weedwhackers at yard sales, but the Still FS 48 was best configured for my needs. Bicycle is a Ross racer (yard sale as well) Now this project is not for the beginner, as nearly every aspect of this project requires major fab work. I machined five grooves on the engine crank nut/shaft driver. The jackshaft has a Subaru power steering pulley on the right, and a cable operated tensioner. The belt primary is also smoother than chain at 10,000 RPM! The secondary drive features a 12T three pawl freewheel to a 52T final. Overall gearing works out to about 36:1. Now 23ccs is pretty puny, so I build tuned exhaust and intake. Without these mods it would run about 15mph an pull no incline on it's own. I modified the intake three times to get what I want. Now it'll pull comfortably from 8 to 20mph at even half throttle. Today I hit 24.5mph with a slight tail wind, that however, is well over 11,000 RPM, so I won't make habit of it. It will pull hills well, and will even take moderate trail work at about 10mph with occasional pedal assist. Weighs in at 50 lbs wet and am getting 140mpg with 14mph trip average speeds.

 

[Dave31]

Very nice Buzzerbiker I like it Welcome to the forum glad you joined us.

 

[Buzzerbiker]

Hi Dave31, thank you! I have added a few upgrades since these photos. I put a foil backed foam engine cover on to cut down on noise. The exhaust now has a second silencer, (a mini glasspack). The intake is what really howls though, the cover really helps and I continued the "rat" black paint scheme with the adds. I am not totally satisfied with the intake, am stihl scheming future mods. Once I got this bike running the WORK really began, lots O fun though. My best upgrade however was building a rubber isolated goose neck for the handle bars,"comfy". I will post a pic of that part later. Thanks again.