Dyno Tuning the Suzuki GS500

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 is located at 1038 W. Little Creek Road in Norfolk, VA. They specialize in sales, service, and performance tuning of import motorcycles.

 

Check out more Suzuki GS500 posts! 

By | 2017-09-13T02:07:52+00:00 January 13th, 2015|Motorcycle Projects|9 Comments

About the Author:

I'm a lifetime car guy with a broad interest in just about any type of self-propelled machinery, and racing. I have a soft spot for under-appreciated marques, which often gets me in trouble with oddball projects.

9 Comments

  1. Bert April 15, 2016 at 5:23 am

    you mention the bike had a stage 3 jet kit but do not tell us from which manufacturer. Who’s stage 3 jet kit.
    I’m guessing dyno jet or factory pro. Let us know. thanks,

  2. Mikkel Fessel August 24, 2016 at 8:52 pm

    Hello there. Very informative. I have been spending the last couple of days googling, and reading around on different forum about Dynojet kits, / stage 1-3 / etc. My question is this. I have an 2008 Suzuki gs 500 E. None of the dyno kits I have found on eBay has the stage 3 kit (for this make/modal), and after writing to Dynojet kit, I got the answer that I can use a stage 1. But that is not what I understood from reading around on the internet. I have a KN filter / Iridium spark plugs / full Yoshimura RS 3 exhaust.

    Is that something you could help me out with?

    Regards

    Mikkel

    • Dan Hankin August 25, 2016 at 12:30 am

      Hi Mikkel. I’m not sure of the carb differences between the old GS I had and the later bikes like yours, but companies like Dynojet do a ton of R&D on their kits. There may be a reason they only offer a Stage 1 kit for that bike (i.e. drivability, tuning issues, etc.). Even in the case of my GS500, the jets that came in the Stage 3 kit were far too fat for the bike to run well, even with full exhaust, pod filters, and advanced timing. We ended up having to lean out the jets quite a bit.

      If it were my bike I’d go ahead and install the Stage 1 kit on Dynojet’s suggestion and tune it from there. You can always richen the mixture a little or put fatter jets in down the line, if necessary. You should feel improved throttle response, and hopefully some more pull in the middle/top of the power band after the jets are done. If you don’t have access to a dyno (or cash for dyno tuning) the next best thing is hooking the bike up a wideband 02 sensor/gauge to look at the AFR under varying loads. Make sure you’re not leaning out too much at WOT. Ideal AFR is about 13:1, but it will fluctuate under different loads. Good luck! Let us know how it turns out.

      • Mikkel Fessel August 25, 2016 at 1:05 am

        Well Dan Hankin. Thank you very much for a quick and good answer! I will go ahead and try it out. I am not really looking for top speed, but there is always room for a better response and more torque:) It will take some time before I do the upgrade, but once it’s done, I will try and post the result here for you and any other wouldbe dyno fans using the “newer” modal of the GS.

        Thank you again!

  3. Dan Hankin August 25, 2016 at 12:34 am

    Also, if you’re not already a member of the board at GS Twin, I highly recommend it. I’m no longer frequently active on the board, but I’ve always found the site to be a great resource. http://gstwins.com/gsboard/

    • Mikkel Fessel December 7, 2016 at 12:01 am

      Hey Dan. So I finally got my dynojet kit. Just waiting for some free time, so I can take it to the guys who are going to install it. I have a question, that maybe you could answer for me, if it’s not a bother. Ignition timing. Is it something worth looking into? I mean, I read that one of the best ways to do that is :”Dynamometer tuning” ? Since they are going to use the dynamometer to best install the dyno kit, would that be relevant to bring up?

      Thank you for your time

      Regards

      • Dan Hankin December 7, 2016 at 1:28 am

        Hey Mikkel! I had made so many tweaks to my bike it would be tough to say how much of a difference just the timing made. The thing with small displacement engines is that no basic bolt on part or minor change is going to make a huge power difference.

        If you can get your hands on an advanced timing rotor I’d go ahead and have it put in along with the jet kit prior to tuning. The aftermarket rotors are pretty rare. You can drill an advanced timing slot in a stock rotor (that’s what I had done). If you don’t want to risk messing up your rotor you should be able to find a used one pretty cheap. I’m no longer active on this board, but it was a good source of cheap used parts when I was: http://gstwins.com/gsboard/index.php?PHPSESSID=5c7c6d0b7fb5cc0c68145a053cadedf0&board=2.0
        I think there used to be a guy that was drilling advance rotors and selling them on the board. Don’t remember his name though.

        All of that said, if the timing advance is out of your budget or you can’t find an advance rotor I wouldn’t sweat it too much. It’s super easy to install in the future if you find one later on, and you very well may be happy with exhaust and a jet kit with a little tune. Good luck!

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