Currently running an 8 range plug, and the car started misfiring above 6200 rpms at the last HC race. It got gradually worse but was intermittent. I've got some 6 plugs, but what else should I be checking? Anyone have an idea? I've checked the 8's, and they are a little white, but the electrode is still in fine shape. (Car doesn't see many street miles anymore) The dist cap is in fine shape, and all the wires are less than 2000 miles and 2 races old. The timing is advanced as far as I would trust it (the 4th mark), but I could back it off if I wasn't missing something else. Thanks in advance.

 

Does your tach jump around? or has it been jumping around before the mis fire started. Also, if you are running NGK and you go from 8 to 6, you are actually going hotter.

 

What car and preparation level are you running?

If IT spec, you should be fine with the standard (OEM) plug range.

 

What brand of plugs are you using? With NGK, 8 is colder than 6, but it's the opposite for Bosch.

 

did you check the rotor? also i would still check the plug wires for arcing. it would also help if you told us the mods you have done to the car and the ignition products you are using.

 

Thanks guys.
It's an IT spec motor, but it looks like I've cooked the plugs in the 90+ degree heat, no oil cooler having weekend at road atlanta.
Rotor is good, wires are good. Tach hasn't been jumping around, and when it misfires, it certainly isn't, cuz that's when I looked down wondering if it was the rev limiter or something. Ignition is stock, NGK plugs and wires.(that will be replaced before the car is fired up again.) I'm going to back the timing off for the next race, because the problem is intermittant and only under load above 6k.
I'm tracing a vacuum leak. Might that be a possibility as well?

 

Sounds like what was happening when my ignitor let go. First a high RPM miss, then the aforementioned tach craziness, then it stopped working during my second run of the Petersburg Prosolo and I had to be towed home

Obviously these are vastly different cars, but ignitor failure in Hondas is pretty common. I now carry a spare.