Nitrous

Primera GT P11 thought i'd sorted it - oh well. Any constructive advice welcome, fitted magnecor HT leads, new distr, cap and rotor arm - misfiring cured. Brill. Then noticed a surge - flatspot - surge whilst on 75hp boost. Phoned highpower, trev suggested colder plugs. Phoned NGK they said BKR7EVX to replace existing. I have BKR6EY's but i didn't have that info to tell them. Bought them, fitted them and yep... it misfires horribly. I can only assume NGK dolly bird in tech told me the wrong part number. What else could be causing it? I'm putting the old plugs back in tonight just to check it isn't something else. I only had the bottle filled this aft but it's been running fine off nitrous with the VX plugs for the last 2 days.

Could be:

Rich, or weak... Dodgy installation? Dodgy wiring? Fuel pump inadequate Fuel jet blockage Solenoids mounted in a too hot place... Nitrous line routed in too hot place Failing or inadequate ignition system... Failing plug(s)

Check for correct fuel pressure under WOT condition whilst operating the fuel solenoid IN A TALL GEAR AT MAX POWER RPM..

Use stock plugs (no fancy platinum ones or anything!!!) but one or two grades cooler (an 8 in place of a 6 or 7) DO NOT USE EXTENDED NOSE TYPE! Also avoid grooved, twin or more electrodes, platinum etc.
To check for inadequate ignition, temporarily use plug gaps 1/3rd smaller than stock. Its "harder" to fire a plug on nitrous, so leads, coils, caps, etc all can failo and earth the spark before it gets to the plug!

Check for enough nitrous (weigh it!) and that liquid nitrous issues from the solenoid, and the same with the fuel.
Retard ignition by a few degrees (start with say 4 or 5 and re advance gradually as you test.

Use good (high octane as you can find) fuel.

If all that is correct it WILL work!

If not its probably too rich. Trev likes "rich"!