The Perfect Tune

Speed’s Spotlight

For a carbureted bike, and there are still plenty of us with them, the question of whether or not to get that dynamometer tune is a no-brainer. There’s just no better way to tune a motorcycle than to put it on the dyno and run it through its paces. Sure, you can try to set up a carburetor yourself, changing jets and slides and springs and needle heights and making small adjustments until you’re blue in the face, road-testing each change again and again until you think you have it right. You’ll never be absolutely certain, of course, never having a clue as to the exact air/fuel ratio at any given throttle position. But on a dyno, with its exhaust-gas analyzer, that carburetor tune can be made as close to perfect as possible.

These days, of course, most riders are on fuel-injected bikes and the situation here, in an auto-tune world, can be considerably easier. “Can” being the operative word. With the advent of all those auto-tune systems currently available, it’s easy to believe that the perfect air/fuel mixture is all right there. Install one of those systems, download a pre-written map approximating your setup and parts selection, the pipes, air filter and so on, and then go for a ride. Presto, after a few miles riding to establish a learning curve, pun intended, the bike automatically reaches tuning nirvana. And in many cases that can be true. But, and this is a big “but,” in just as many cases that’s not going to be the case.

“There are lots of reasons for that,” Jason Hanson, the dyno magician at Speed’s Performance Plus explains. “But the main one,” he says, “is that all those auto-tune systems have built-in limitations. They’ll allow a fuel/air mixture adjustment by only a certain percentage either way, rich or lean.” Now, if the motorcycle in question is a fairly stock bike and set up with only a set of popular slip-on mufflers and a free-flow air filter, and it’s a fairly new bike in perfect mechanical condition that auto-tune, working within its allowable parameters, will most likely adjust things close enough. “But any deviation from any of that,” Jason warns, “is where the problem starts.” Where you begin to run into trouble, he says, is when the downloaded map isn’t quite close enough and the auto-tune can’t compensate within its set limits. No two bikes, even running identical aftermarket parts, will be exactly alike. They’ll most likely require completely different tuning maps to start with. Add cams, big-bore kits, wide open pipes, cylinder head work, or any number of other variables into the picture and auto-tune will be taxed to the max trying to keep up. “And those short, wide-open pipes so popular now can be especially troublesome,” Jason adds. Reversion waves in the exhaust flow will actually suck cold air back up into the pipe, indeed all the way up into the cylinder heads, and completely flummox the O2 sensors. They won’t know what to make of those intermittent clean-air readings. See where this is heading? Incidentally, the reason for limiting the automatic adjustment possibilities of an auto-tune is to assure that the system will run in a “safe mode” should the motorcycle develop problems like a faulty injector or a massive air leak. In those situations the O2 sensors would detect an overly lean mixture and call for a maximum infusion of fuel.

What’s the answer here? Like we said at the beginning, the best bet for a perfect auto-tune is to start with a custom-tune mapped specifically for the motorcycle. With a custom map specific to the bike, professionally written on a dynamometer and on-the-money correct, then the auto-tune can be turned on to make minute adjustments as needed. And from that perfect starting point the auto-tune will work like a charm because it will be working off a map that’s already perfect for the motorcycle. Tuning doesn’t get any better, or closer, than that.


Speed’s Performance Plus

(605) 695-1401 – MN

(605) 695-2272 – SD