As the saying goes, there’s no replacement for displacement. There’s truth in that statement, which is unfortunate when you’re working with 487 air cooled cubic centimeters.
We didn’t have pre-modification baseline numbers for our 1993 Suzuki GS500, but a little research revealed the average stock GS500 puts down about 39 wheel horsepower. That’s not a lot in comparison to the average modern sportbike, but it is enough to have some fun without getting yourself into a whole lot of trouble. That said, after completing a bunch of work on the bike we were hoping to put down a few extra ponies and fine tune our Suzuki GS500 on the dyno at D&D Import Cycles.
Prior to visiting the dyno we had opened up our Suzuki’s factory Mikuni carbs and re-jetted them with a stage III jet kit and pod filters. The ignition was also re-drilled with a five degree timing advance, and we installed a full Vance & Hines Supersport exhaust system.
With the bike warmed up to operating temperature and strapped down on the Dynojet 200, dyno operator Jerry Peak shifted the GS500 up through the gears to an aggressive fourth gear roll on the throttle. Fourth gear was used for the power pulls because it’s the point at which the ratio between the rotating dyno drum and the Suzuki’s rear tire is closest to 1:1. The base pull calculated 44 horsepower at the wheel – already a very good improvement from the stock estimate. The graph also showed the Suzuki twin to be running rich.
Peak suggested replacing the 134 main jet that was installed as part of our jet kit with a smaller 124 main. The smaller jet leaned out the Suzuki’s mixture a bit more than we’d like at low rpm, but kept the twin burning at an ideal air/fuel ratio of about 13ppm in the operating range of the power band. On a carbureted engine compromises like this are often an unfortunate necessity and a lean condition is far less dangerous at idle than it is at WOT. The smaller jet also provided a 1.1 horsepower gain for a peak 45.1 horsepower at 9,200 rpm, and cured an off-idle stumble. The power curve recorded by our GS500 is pretty smooth, but had there been any sharp peaks or valleys the dyno would show us where they were so we could attempt to tune them out.
With 45.1 horsepower at the wheel I’m not likely going to run down a Ducati at the race track, but the extra power combined with an improved throttle response, better breathing, and linear power delivery sure makes it fun to try.
D&D Import Cycles and Triumph is located at 1038 W. Little Creek Road in Norfolk, VA. They specialize in sales, service, and performance tuning of import motorcycles.
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