[BSR-1]

Originally Posted by Beauwulf

On a DI engine, the MAF registers the total air through the intake and the ECU basically divides that amount by 6 and fuels accordingly. In a throttle body injected engine, the fuel is added to the airflow and mixed before it gets to the intake plenum area so, each cylinder gets all the air with fuel it can pack in. If one cylinder flows a bit more, the mixture is still the same.

In a bike engine, with individual carbs, each cylinder will still fuel for the amount of air it can pack into the cylinders. CV carbs are best at this because they work on vacuum in each intake so if one flows more air, it will still fuel more keeping the mixture right.

In our DI engine, (or FI motorcycle engine) if one cylinder gets more air, the ECU is still only fueling for 1/6th of the total airflow so, that cylinder could be lean. Add turbulence in the intake tract to that, which can cause incomplete burning of the mixture, and you could run way lean and hurt stuff... mostly exhaust valves. Better a safe tune than broke from buying new parts.

Thanks for the explanation. That may make a difference.