iv got b20b with 12.5 compression
it was running fine on NGK iridum BKR6EIX-11 on its base tune. then i switched to NGK iridum BKR7EIX-11 (same base tune). ever since iv changed the plugs. it starts running like crap like missing etc on light throttle and surging. the plugs were at 1.1mm when new. i regapped them to 1mm (0.040") same thing.

what everyone running them on high compression motors?

iv got another b18c similar compresion same plugs but no issues

so inputs. could it just be a simple retune to suit plugs

 

it was running fine on NGK iridum BKR6EIX-11 on its base tune


Why not get it tuned properly then see what happens

 

check to make sure all your plug wires are installed firmly and correctly. If yes and if possible, reinstall your old plugs and see if the problem goes away.

 

the reason why its on it base tune. cause the motor just getting a run in first before final tune. car runs fine on old plugs which are the hotter plugs. the leads etc are firmly on

 

You should be on 7's to begin with, try the copper 7's.

 

If you've swapped the plugs back and forth to confim this, try swapping one new plug out with an old plug. Keep doing this one at a time to see if it goes away and what plug may be the cause of it. It may be that one of your new plugs is bad but it's unlikely that the heat range is your problem.