My brumby (in Oz) developed a misfire at cruise recently.
It uses about 1mL of oil per km, detonates in warm weather unless an octane booster is added (which was done for two tanks prior to this tank of fuel), is run on 98RON fuel. From memory the timing is set at 4° btdc, anything more and it pings hardcore.
No issues under load or when accelerating slowly or going hard with the misfire. Just at cruise it misfires giving small jolts in loss of power.
The old plugs were pretty toasted so new plugs went in with no change with the issue.
I’m open to ideas on this one as I can’t work it out and I want to keep driving it before a long winded EJ conversion happens to it.
Cheers
Bennie