They told me that the lean situation might not be a problem, but it could be fixed with either a Power Commander or a race ECU. I decided to keep the bike for a while and see how it went with just the standard fueling. I also wanted to see what it was like with the db-killer in and out.
It didn't take long before I decided that the engine seemed to be lacking a bit low down, and was also a bit snatchy on the throttle, so I called Peter Stevens up and spoke to a chap about my options. He said they had the ECUs in stock, and I could get one fitted immediately - specifically designed for my bike. Within a few days I had the ECU on the bike and this time they reported that it was running slightly rich, which is apparently a better situation than slightly lean. The mileage I get now is about what it's always been - 180km from a full tank until the low fuel light comes on. Although my last tank I got 200km before the lamp came on.
The ECU definitely calmed the bike down in the lower ranges. It's a lot smoother from idle to 4k and no real dip in power there any more. Of course in the upper ranges it screams like a banshee and has bucketloads of power - as always. The other thing is the sound it makes when idling cold. Since fitting the ECU, it does this kind of sine-wave idling thing where it sits there going brrp brrp brrp brrp instead of just staying at a constant rpm. Sounds awesome.
Not knowing much about bike electronics/software I came to the conclusion that the Power Commander is a device that sits between the sensors and the ECU and tricks the bike into thinking that conditions are different to what they actually are. It seemed like you had to find a decent map suitable for your bike, so I preferred to go with the after-market ECU, which seemed like a more straightforward option. I'm certainly happy with the results.
I experimented with the db-killer out, but eventually came to the conclusion that it's just too loud for me. I ride every day, and always wear earplugs to cut out the wind noise etc. but I found the noise level when I rev the bike out to be just too intimidating. It becomes so loud that it deters me from revving. I prefer to have a quieter sound that doesn't sound like a jet engine, yet is loud enough to make cars notice you - which is my main motivation for fitting the exhaust in the first place.
Interestingly, the Buell was a lot better at making itself heard when doodling through the traffic, simply because of the bass thump of the big twin. The four-cylinder sound of the MV is not as bassy when idling, but a hell of a lot louder when flat out. Most of the problems I find with traffic not seeing you occur at fairly low speeds, when the engine is in its low to mid range, so the twin is better from that perspective. Of course the Buell ran out of steam at 6,500rpm, which is just about where the MV kicks in! Hence the 52 horsepower difference, I suppose...