Guys,
Some of you may recall that a few months back I had some problems with
spark plugs that spawned several related topics and questions. I had had a
set of Autolite AP45 platinum plugs in my Tiger's engine for quite some
time, perhaps 15-20k miles or so. Noticing that it was idling rough, I
pulled these old plugs and found that two - #1 & #8 were missing most of
the center electrodes. I got lots of advice relative to spark plugs, most
of which pointed to NGKs as the best. On the other hand, Autolite seems to
have slipped their quality since they were bought out and the manufacturing
transferred to Mexico. However, on advice attributed to Dan Walters, I
bought and installed a set of Autolite AP124 plugs, which I believe are for
a truck application and presumably run pretty cool - which is a good thing
for race use too, which is the application Dan was probably recommending
them for. The AP124s seemed to work well, although I noticed they didn't
protrude as far into the combustion chamber as the AP45's and other plugs
I've used. I expected this to have some possible consequences at idle and
low rpm, but it wasn't noticeable at first. Over the past few weeks though,
I have noticed more and more hesitation pulling away from a stop until the
rpms get going a little. Monday, I made a trip from Vista to Santa Barbara
and back. The engine ran great on the highway, but yesterday when I drove
it, it was idling extremely rough. Actually, it idled fine until it got
hot, then rough. Aha it though, too rich. Leaned it out, but that made it
worse. Played with spark advance, more helped, but when it idled best the
advance was so much that would fight the starter and would scarcely start.
I got home OK, but was thankful for a minimum of stop-and-go traffic.
Today I pulled the plugs. Some looked very clean, some looked so-so, and
two looked pretty carboned up. Back to Pep Boys to get a new set of plugs.
But which kind this time? At least the AP124s had lasted a long time. I
tried to get some NGKs, but they didn't have them in stock. OK, what about
Bosch? These they had, either the regular platinum (4226 aka DR 8 BPX) at
about $2 each, or some new fancy platinum quad-gap plugs for $5 each. I
bought the $2 plugs.
BTW, all of these plugs are resistor types with about 6k ohms resistance.
Also, I'm running an MSD and have spiral wound spark plug wires.
After removing all the old plugs, and before installing the new ones, I ran
a compression check just to be sure. Yep, 190-200 lbs/in on each cylinder
(cold). I had previously indexed the AP124 plugs and had the cylinders
marked on my indexing tool. Right away I find out the Bosch plugs index
about 45 degrees offset from the Autolite plugs. Did anyone tell me this
before?? Oh well, after considerable trial and error I get eight in
pointing pretty much the right direction. Well, the new plugs did the
trick. The engine idles smooth again and pulls from a stop without
hesitating, sputtering, missing, etc. How long these will last I'm not
sure, but I hope they last longer than the AP124s did. The AP124s may be
just the ticket at the track, but for street use, they seem to be a bad choice.
Well, just thought I'd pass on a little more of my experience spark plugs
in case any of you are having similar experiences.
Well, TTFN guys,
Bob
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