Running lean will really set off the spark knock and as others have said, it can cause major issues with the internals of the motor.
With Harleys, the first thing buyers do is to ditch the air cleaner for one that breathes better. Along with that we replace the exhaust for louder sound and better performance.
After doing this you have to buy a tuner for the ECM and either get a dyno proven canned map or have the bike setup on a dyno. All of this usually sets one back, depending on what systems you buy, $1,500 to $2,000. I have to wonder why we have to do this on a brand new bike, but that's what we do. The tuner alone can cost upwards of $500.
I see the same opportunities on the M3W with the S&S wedge motors. I'm sure with the correct tuner controller, one could get the fuel ratio to a livable point that the spark knock would go away and the motor would run a lot cooler. There may be a tuner already available for this motor and ECM because S&S has been making the wedge motor for some time. If anyone was interested, I would check with TTS Mastertune, Fuelmoto or Power Commander.
My Harley bagger has a 110” / 1802cc twin cam motor from Harley. I bought the TTS Mastertune with the vendor’s dyno proven canned map. With the tuner kit you get a module that allows communication with the ECM along with all the necessary cables to hook up to your laptop. I did all the updates myself with my laptop. I downloaded the Harley map and uploaded the new map. Unlike some of the other tuners, nothing stays on the bike after the upgrade. My bike runs much better than it did stock and with two up on normal riding I get in the high 40’s for mpg.
One thing that the TTS Mastertune allows is on the fly recording of the fuel and ignition while you’re driving. This is kind of like an auto tune part that TTS offers. Some have gotten better results by tweaking after the fact, but my canned map was dyno proven on probably 15 to 20 exact same bikes as mine, AC and exhaust setup.
So I would investigate the opportunity to do this on the M3W’s. I’m sure some here have later Harleys and are familiar with the tuning process.
