99 FLTRI, 21G cams, PCIII, pinging on light load

[PC_Hater]

1999 FLTRI, Andrews TW21 cams, PCIII, engine breather is a pipe to the ground, Supertrapp 2:1, HD 6R12 spark plugs

The bike has been pinging at low revs light load for a couple of years and many thousands of miles and I am tired of it. There is no ping at high load or high throttle or both.
The most recent tune was done by DynoJet UK. The tuner removed as much timing as he could and still the ping was there. Put in a lot of fuel and still the ping was there.
The performance on the dyno was very poor like that of course so after some discussion we agreed he should use his skill and judgement to make it better than it was when I brought it in. Which he did. It is still not right though and now we have got back from touring Norway it is time to fix it. I certainly wasn't going to mess with it before we went!

Using higher octane fuel doesn't help.
The oil needs topping up once between oil changes but the usage really is low.

I did a CCP test and got 160psi in each cylinder.

After the CCP test I checked for trouble codes with the engine check light and got '25' for the rear ignition coil. This would be correct because I removed the fuse for the fuel pump during the test and that fuse is in the coil circuit too.

I was hoping the CCP test would show a previous owner had fitted high compression pistons that wouldn't play nicely with the cams, or a trouble code would show a dodgy sensor, but no. All I know is 'something' isn't quite right.

Does anybody have any idea what I should try next?
Colder spark plug? If so which one?

[Don D]

Get into the timing table and see what numbers are in there under the conditions where it pings. May need to highlight the problem area and decrement the numbers

[PC_Hater]

The timing tables are mainly 0 for all throttle positions and all rpms and are identical for each cylinder.
0% throttle has up to 5 degree advance at all rpms.
80% and 100% throttle have 1 or 2 degrees of advance at some rpms.

There is no timing retard in the troublesome 1500 rpm to 2750 rpm up to 20% or so throttle region.
I suppose I get to play with that this weekend.

[Don D]

Take it out slowly and test warm.

[FLTRI]

Consider this:
Detonation (ping) generally occurs @ high load. You are noticing the ping with light load.

Higher octane didn't help - points away from detonation.

Retarded timing didn't eliminate the ping - points away from detonation.

This leads me to question if there isn't something else going on that is making the ping sound?

Piston slap sounds like ping-type light rap when cold and usually lessens with heat.

Certain parts on the bike can make pinging noise at specific vibration harmonics which you go through when you add/wick the throttle.

Hope you find it,
Bob

[yositime]

What FLTRI said and, I had a car with similar symptoms and found a tiny vacuum leak, just enough to affect off idle and part throttle, but not enough to noticeably affect idle or WOT.