My ’20 107 does that. I run 91 or 93 when available, and have added Lucas Octane booster, but that had no effect. I’m now running a Fuel Moto tune via Powervision and eliminated some of the rattling/pinging when accelerating, but I still get that distinct Tink Tink when I open it up. Sounds like two small rocks hitting the inside of the front fender, only it’s not, because it is repeatable. As posted above I’ve reached the conclusion that it is such short duration due to the knock sensors causing the ECM to retard the timing.

At least that is my speculation.

 

I run US 93, 99% of the time.
If I go to a gas station and an old lady is filling her Saab, I stay away from that *****!

 

That's exactly how I would describe the sounds I'm hearing. A metallic two-beat, "k-tink" kind of thing. Has to be the same, maybe it's simply a ping... I refuse to believe that this is something that is simply "how it should be" though, so now the question is what to do about it...

 

Roger that, maybe I should strive to only fill up with EU98 and see if that helps... Only, that **** isn't available everywhere... Like, do I need to carry a ****ing jerry can of premium with me wherever I go?? That seems less than optimal...

 

To be clear, if I ran 91 octane, which has happened on occasion, still I have no pinging. I'm at around 11.5:1 compression for over a year.

 

I’ve been sleuthing it for a year and a half. All I can tell you is that not all M8’s do this, but some do. I’m at 17,000 and plan to keep taking it on trips. I think it’s a peculiarity of the beast. I’ve run datalogs for Fuel Moto and I think further tuning is not the answer.

 

It's my opinion that Harley tunes their engines just on the edge of pinging for the peak horse power and torque then relies on the knock sensors to keep it under control. This probably works fine in most conditions but the "plink" comes as the ambient temperature and humidity reach a certain point.
I could be wrong but it is possible the tuner used the default timing table and adjusted the fuel and air mixers. This is what happened when I had my Twin Cam tuned. I would talk to the tuner to see if they can fine tune your timing tables. They could use knock events on recorded runs to fine tune the timing tables in the appropriate ranges.
These days I'm not looking for peak performance so I'm not afraid to sacrifice a little power by pulling some timing off the tables for something that runs a little better when it's 100f out. My primary use for my bike is long range touring. As I said above, I'm not too concerned with the occasional "plink", but one day my obsessive compulsive side will make me do something about it.

 

IMHO, the factory tune is done to get the best out of 93 octane which some states have. Then the knock control is designed to retard spark when it detects knock, which will happen under load with less octane. You will still get a slight ping though. In my experience it takes about 1 oz of Lucas octane boost per gallon of gas to notice a ping reduction.

Remember, octane does not add power, but it allows the motor to develop more power without pre-detonation. As such, lower octane fuel, will result in slightly less performance as knock is detected and the spark retarded yo reduce the knock And consequently reduces power.

 

Does your bike do it only at higher altitudes? Also how low do you allow the rpm’s to go before downshifting?

 

After chasing this identical issue since late 2020 I’d first like to say this is probably the most constructive discussion I’ve seen here on the topic so thanks to all for that.

Couple of observations in the case if my 2020 107.

In stock configuration when new, the bike would lightly ping/rattle consistently through the rpms when accelerating the least bit “aggressively”.

I always run name brand 91, usually Exxon/Mobile because that’s what’s available. Shell 93 where available.

I tried adding 2oz (one bottle) of Lucas octane booster per six gallons, which they advertise boosts octane level “3 points for 4-6 gallons” . Did this periodically even after adding a Powervision tuner and running a new tune after datalogs were sent to Fuel Moto. The octane booster at that concentration had no impact on pinging whatsoever. I haven’t tried two (or three) bottles per trigeezer’s recipe for one ounce to one gallon. I may do that.

It wasn’t till I was on a trip last fall around 11,000 miles on the bike where
I recall first hearing the “tink tink”. If memory serves, I needed to hard accelerate in heavy traffic in warm weather from maybe 2500 -2800 rpms through fifth into sixth gear to 85 mph on an expressway ramp that I first heard it. Wondered if it was rocks hitting the inside of the front
fender, till it did it on the return trip identically, and very occasionally will do that in similar riding conditions.

Interstingly, the consistent ping/ rattle (like “castanets“, think flamenco dancer for us old farts) when accelerating seems to have largely diminished.

One interesting point, when I sent data logs to FM their observation was that any knock events they could see in the logs where considered “normal” and they were surprised that I could even hear them.

Also, I can’t say for sure if I was ever able to log the “tink tink” events last fall when I was adding the tuner.

ETA: I had the two clutch side spark plugs out last week and it’s pretty safe to say the bike is not running lean.