Part #1: Purge The Surge
When I bought my current Bandit it suffered from the well-documented low-rev surging issue. It wasn't terrible but it was there and neither of my previous Bandits did it. Initially, I tried the basics: A full service with new plugs, air filter, throttle body synch and TPS calibration. All of which made no difference. I tried running on E5 petrol instead of E10 which also made no difference. I tried injector cleaner, again no difference. There were no stored error codes and otherwise the bike ran perfectly.
And so a process of elimination began. First I fitted an O2 Sensor eliminator which made no difference: Fuel consumption and performance remained exactly the same, as did the surge.
Next up was the PAIR system. I didn't actually remove it, just blocked it off so it was still there but not functioning. Again this made no difference to the running but it did make the exhaust smell more “Fumey” when sitting in traffic, so I reconnected it.
And then, after a lot of research, I decided to remove the secondary throttle flaps. This didn't cure the surging either but it did make a noticeable difference: On a standard bike the secondaries shut everything down at 7,000rpm but without them the engine keeps pulling right up to 9,000rpm. The throttle response is more immediate as well. And removing the secondaries and remapping can easily net an extra 15bhp with a slip on exhaust and performance air filter (more on which below).
But none of this sorted the surging and I gradually noticed that the problem wasn't there when the bike was cold, on the cold map it ran just fine, so it was clearly a fuelling issue.
There are various tuning modules on the market which allow for adjustment of the fuel map. The Power Commander is the best known but the Healtech FI Tuner Pro does a similar job for half the price if you don't need the optional features of the Power Commander.
Set up is simple, the unit plugs into the bikes diagnostic port and then taps into two of the main ECU wires. The Healtech unit itself is matchbox sized and simply velcros to any convenient spot under the seat. It has a USB port to connect to a laptop which, having downloaded the free app, gives pretty much full control over the fuel map. It is recommended to use an O2 sensor eliminator and a Timing Retard Eliminator which forces the fuel system to use the unrestricted 5th gear map in every gear.
The Healtech also allows on-the-fly monitoring and so, with a tablet PC taped to the tank, I was able to ride the bike in the “Surge zone” and see exactly where on the fuel map the problem occurred. It turned out that the problem area was the 2,000 – 2,500rpm range at 0-2% throttle openings. And so I was able to adjust the mixture at exactly those points. I just added 10% extra fuel in the problem area and the surging is gone. So yeah - the Healtech FI Tuner Pro. Recommended.
Part #2: Moar Powah!
With the FI Tuner Pro fitted and the secondary butterflies removed I was already halfway to a decent power increase so I decided to carry on to a "Stage 2" tune. First up was the air box mod: Cut the top off the lid leaving the outer part to retain the filter. Next was a K&N SU-6000 filter, this is actually the listed part for the Bandit 1200 but it fits the 1250 air box and has 20% more filter area than the official 1250 part. It's also the filter that Dale Walker supplies with his 1250 tuning kits, and he's spent more time tuning the 1250 than anyone else, so that's what I went with.
Most Stage 2s use a slip-on silencer with the standard downpipes and I did the same. I looked at the various systems and found them all to be much of a muchness: They're all lighter, smaller and less restrictive than the OE system. I went with a Delkevic X-OVAL 343mm: UK road legal, cheapish and decent quality. It even looks like the Yoshi can that was once offered as an official accessory.
With the hardware complete it was software time. I started with a map shared by someone a running similar set up. And it was pretty close save for a hint of lean surge around 2,500rpm / 35mph and a slight dip in the power delivery around 7,500rpm - both fixed by adjusting the fuelling in the respective areas. It's a work in progress and ultimately I intend to get the bike dyno tuned, but for now it doesn't feel far off the mark.
Update: After some messing around, I decided that I didn't like the open airbox: I didn't like the noise and it felt like the bike had lost some bottom end. So I went back to the standard airbox, but keeping the K&N. And I like this set-up a lot. I'm not sure if there's more grunt than stock but there's an immediacy that wasn't there before. Throttle response is instant and fuelling is perfect from idle upwards. Now I just need some decent weather to go and play...
