All you need to know about adjusting your bike’s fuelling – it’s important!
Getting the fuelling right is essential on any tuned bike. But how can you sort it? We check out the options – and the problems with the latest bikes.
Power Commander and a pipe. They go together like pie and pint, vodka and coke, wheelie and stoppie. For almost the entire 21st century so far, it’s been the basic level of bike tuning. The pipe – a full exhaust system ideally, a slip-on can if your other half has restricted the bike spending this month – will save a load of weight, make you look and sound like an utter MotoGP hero, and add on plenty of ponies.
And the Power Commander? Well, it’s there to sort the fuelling, or smooth out the flat spots, or add an extra power band. Or something. Isn’t it? And didn’t your mate say something about having his bike ‘flashed’ instead of fitting a Power Commander? Is that the best thing now?
It’s fair to say that some folk are a little confused about what an ECU flash, a Power Commander, or other fuel injection tuning kit, is all about. Luckily, we’re here to help. Even more luckily, we’ve actually gone and asked some grown-ups all about it…
What’s it all about, then?
So – the basics. Bike engines need petrol and air, plus a spark and some compression to make them go vroom. The lovely folks at Honda, Yamaha, Triumph, Ducati et al, make it their life’s work to provide us with gorgeously-fuelled motos, purring away under us, consuming the unleaded and emitting fumes that are less noxious than a sparrow’s fart. All’s well with the world, and all you need to do is keep putting in the Optimax, twisting the throttle, and perfecting your wheelies on the ring road.
But the minute you alter anything on the engine – the aforementioned pipe, say, or maybe a flash race air filter, different camshafts, inlet trumpets, altered airbox – the factory fuelling won’t be spot-on any more. So you’ll need to work out some way of changing how much fuel is fed into the engine, and at what times.
In the past that was dead easy. Carburetted bikes used small brass ‘jets’ – accuratelymade orifices which let a precise amount of petrol flow through them. As you opened the throttle more jets were opened, and a needle moved out of a large jet, allowing more fuel to flow as the engine hit full throttle. Change these jets for ones with physically larger
holes, and you let more fuel in. Smaller holes let less in. A differently-shaped needle will alter how the rate of fuel changes through the rev range. Simple.
Enter, the hero
The American firm Dyno made its name in the 1980s and 90s with its Dynojet carb kits, which provided pre-selected jets with improved fuel flow to suit different tunes. They ironed out flat spots on standard bikes, richened up lean runners, and gave tuners lots of options for getting carbed bikes running with pipes, cams, race air filters, you name it.
All was good – but by the end of the 1990s, fuel injected bikes were becoming more widespread. And, of course, they don’t use jets. Altering the amount of fuel that goes in is simpler in theory – you just open the fuel injector solenoid for a bit more (or less) time, and more petrol goes into the motor on each intake stroke. But changing the numbers inside the fuel injection ‘brains’ was far more technical than just unscrewing a wee brass jet. Tuning early FI bikes, like Honda’s RC45, was the preserve of the genuine factory race team, with complex, bespoke technology.
Someone had to come up with a simple way to alter the fuelling on these new machines. Enter the Power Commander. This little box of tricks worked on a fairly simple principle – it plugged into the bike’s wiring loom between the fuel injectors and the ECU, which let it intercept the electrical signals to the injectors. Dynojet could whisk the stock injector signal away into a little black box, do unspeakable things to it, then send out a new signal, down the wires to the injectors. That new signal could be a bit longer, adding ten per cent more fuel, to overcome an emissions-dictated flat spot, or it could be shorter, taking away some fuel, to cut out rich running due to a different exhaust pipe.
The PC used ‘maps’ inside its electronic brain, which told it what fuelling adjustment to make at which point in the engine rev range. The early PCs were simple beasts, but over time, it’s got smarter, able to make more adjustments, gained a USB port for faster loading times, and Dynojet also added on a heap of accessories, from quickshifters and LCD displays, to different fuel map switches, ignition modules, and secondary fuel modules (for bikes with eight injectors).
That’s the basics then. And it’s fair to say that the Power Commander has pretty much dominated regular tuning in fuel injected bikes. There are other choices of course – Bazazz in the US makes a great range of tuning parts, with traction control and a load of other options. Yoshimura made some tuning boxes for Suzukis in the early 2000s. And for more serious tuning work, and proper racers, something like a Motec 400 setup totally replaces the bike’s stock ECU, taking over all its functions, including ignition advance/retard, the entire fuel mapping process, and stuff like speed limiters, power limits for different gears, running the dashboard, and the like.
Witchcraft
But another option has appeared of late – ‘reflashing’ your bike’s ECU. That is, swapping out the files inside the standard fuel injector control module, and replacing them with ones you’ve written/altered
yourself. On the face of it, it looks like a far more elegant solution: no add-on boxes, total control over the whole bike, with the ability to dump speed limiters and power restrictions in lower gears.
But there are downsides too. It can take much longer to change fuel maps, since each change has to be downloaded into the ECU, and that is slower than altering the numbers in a Power Commander. Tuners we spoke to said that there’s much more work involved in properly mapping the fuelling via ECU flashing. And while it sounds great that you can alter stuff like ignition timing, it’s also possible to really arse things up. Add too much ignition advance at full power, and you’ll properly blow an engine, within a few laps at a trackday.
Returning a bike to standard after flashing isn’t as simple as removing a piggyback box – you need to have the original backup maps to flash back into the ECU’s memory. If you sell the bike, you don’t have an extra ‘bit’ to remove and sell separately if you want to. And once a flashed bike is sold on, the second, third, fourth owners will have no idea it’s been altered, unless the information is properly passed on with the bike. So someone could buy a litre superbike, that doesn’t run right because it was flashed to run with a race pipe and cams, and is now back on standard parts. They’d be spending thousands at a dealer trying to sort it out – with no easy way to tell the ECU’s been changed internally.
What’s the best answer then? Sean Mills at Big CC Racing reckons there are swings and roundabouts. “The best answer is probably to have a Power Commander for the fuel mapping – but use ECU flashing to do the other things that you want – like removing ride-by-wire throttle limits in lower gears, taking out speed limiters, and deleting stuff like closed-loop fuelling or O2 sensors.”
Epilogue
So there you go. Got an older, normally fuel-injected bike? Get a PC on there with a pipe and filter for a simple, easy stage one power-up. Got something a bit fancier and more modern? Then you might want to add in an ECU flash to tailor the bells and whistles, and remove factory limits. Going for the ultimate, money-no-object race tune? Consider a full ECU flash, with plenty of days on the dyno, putting all the maps in there in full – or go the whole hog with a standalone Motec ECU. Then, once you’re all done, give us a bell, and we’ll take it to Donington for a blast and tell you how good it is…