Fouled plug

[ninostr6]

I've been trying to resolve a stuttering issue when accelerating. Checked and confirmed, and all good on mixture, air balancing, timing, and spark plug gap. Noticed that all of the plugs have a good tan tip with the exception of the #3 plug which was found to be black and sooty. Currently running with Champion N12YC gapped at .025. I have also replaced the coil but no improvement.

Would appreciate some suggestions as to the reason why only one (1) plug would be fouled and if this could be reason for the stuttering.

[TRmoment]

You could possibly have a bad plug wire. If you have any spares, maybe try swapping your # 3 plug wire out?

I once had an issue with stuttering / breaking up whenever I hit around 4200 RPM. Went through lots of different testing; all the usual stuff. I didn't think much about the plug wires because they were basically brand new "Green wires" from TRF. Finally, in a "Hail Mary" attempt, I swapped out the plug wires with an older set I had as spares in the trunk and the problem immediately went away.

[poolboy]

I like that idea...I had a bad TRF green wire myself...but if your wire (TRF or not) isn't bad then do a compression test and see how that cylinder compares to the other 5

[ninostr6]

That's interesting regarding a bad plug wire. I also happen to have the green wires from TRF. I'll test with new wire and let you know. Thanks for the advise.

[ninostr6]

Replaced the #3 plug with a new one and swapped the wire from a previous set I had and sure enough no more stuttering. Drove around a bit and #3 spark plug looks good so far.

Thank you all for the advise.

[Ron Kingston]

I installed the TRF greens last night… :-/
I always keep 1 old, long wire as well as a coil wire in the trunk kit, just for this.