4age Smallport missfire

[Whiteke70]

So I ran into a missfire issue recently with my 4age smallport ke70. Just last week I put 98 octane into it for the first time as the previous owner was using 91. The car sat until a few days later where I took it for a spirited drive and one final hoop down the street before pulling into the driveway which is where I then noticed the idle had dropped off 100-200rpm and minor a missfire had surfaced. I just automatically assumed perhaps the ecu was still coming to terms with a now higher octane fuel.

regardless today I went and got new plugs which were identical to the ones currently in the car, in which I discovered the old plugs were quiet black (I did suspect the car was on the rich side). I installed the new plugs where I then turned it over to which it did, but was quite rough and sounded to be missing once again but with also black/grey smoke coming from the tailpipe and exhaust manifold which I didn?t realise was leaking.

I turned the car off and pulled the new plugs out, sure enough black as the ace of spades. Perhaps I?m over analysing the previous few days but what you guys suggest investigating going forward? I would suspect an ignition/spark problem perhaps checking the resistance of the leads, dizzy and also a compression check.

thanks guys

[rthy]

oil getting into the intake/value guides/blow by?

[Whiteke70]

Will inspect the intake closer tomorrow, but otherwise no obvious signs of blow by that I can see? No visible signs of oil in the bay, dipstick still stationed, breather on camshaft cover blows but nothing I’d consider excessive. Oil is still visibly clean maybe 1500km since last service

[rthy]

oil getting in via rings? assuming its a lighter viscosity?

Only other thing would be somewhere in the ignition, did you get around to checking the leads or dizzy/cap?