Gap iridium plugs?

[NickCLotus]

Any thoughts on whether to gap Iridium tipped plugs or not. From what I have read they should not be gapped but default gap is 0.7mm whereas manufacturer recommends a gap of 0.9mm, is this likely to make any difference?

[NickCLotus]

GreenV8S said:

If it was a big difference I'd regap them, but use a wire loop style gauge not the wedge style to avoid damaging the tip. For the small difference you quoted I'd only bother if the new plugs introduced running problems.

Well they do seem to have caused running problems, rough idle and hesitation/fluttering at low throttle openings. Reverting to the old plugs seems to solve the problems so it seems in this case perhaps the 0.7mm gap is too small and needs to go to the manufacturers recomendation of 0.9mm.

Edited by NickCLotus on Wednesday 8th May 17:26

Edited by NickCLotus on Wednesday 8th May 18:02

[NickCLotus]

Panamax said:

So long as you've got enough HT voltage to jump the gap a bigger gap should mean a bigger spark igniting the mixture.

Some may recall the Alfa Romeo "twin spark" engines. Two plugs in each cylinder for better spark ignition. (Not to be confused with aircraft practice where two completely separate ignition systems operate simultaneously for safety reasons.)
...

Bearing in mind that the smaller gap did not work well, might be worth opening the gap out to say 1mm or even more as these are Iridium tipped plugs and so not likely to widen out any during their lifetime.

[NickCLotus]

New iridium tipped plugs now refitted but gapped to 0.925mm, running much better. Looks like this was the cause of the problem all along.

[NickCLotus]

Unfortunately that didn't completely solve the problem. Hesitation when driving at light throttle openings is better but rough idle is still there when warm.