I agree that if you have black plugs, you possibly might not get a good enough spark at the electrodes of the plugs and therefor not burn all the fuel-air mix in the combustion chamber, but this will leed to an overall poorly running engine even under normal driving conditions. Fresh plugs always make a difference - I've seen up to more than 4 horses gained on a dynojet with fresh plugs in an engine. As far as the fuel requirements for your EX (it would have a single cam VTEC engine), I'm pretty sure it needs 91 or better octane fuel (my D16Z6 in my 93 si needs premium according to the owners manual) When I first got the car I mistakenly put regular in it and it pinged like crazy, even though the timing was set properly. One thing I always notice in most honda motors is that they carbon up pretty heavily when I pull the heads off of them, especially when they're driven hard, or mostly in stop and go traffic.