Missfire

Seth, You cleaned the plugs, make sure they have no small deposits stuck down in around the porcelin and the spark plug threaded body grounding them out, my next question is why such a large gap? .031 is stock, with the MSD you get a little hotter spark but .050 is a bit excessive, are you also running an aftermarket hotter coil? I would set them back to around .031 and try thay, with the wide gap its just working the system harder to throw the long spark and any weak link is where the spark will take a path to, bad wire insulation, cap, ect before it goes to the plug.
Also with the bad gas its possible you got some build up on a valve and its not seating causing a cylider miss, you could do a compression check to verify all the cylinders are up to snuff. Also give the cap a look inside to see there is no cracks or carbon tracking between contacts.
Its doubtful but worth asking, are the plug wires on correctly, none crossed at the cap or on the plugs? Good luck.

.050 was what the plugs where at. I will adjust them to .030 ad give it a shot. I am running the MSD Blaster coil with the ignition box.

I will borrow my friends compression tester, and see what happens. Maybe try a carbon cleaning system, along with that fuel dryer.

I will also inspect the cap. Thats a good call.

. Maybe try a carbon cleaning system, along with that fuel dryer.

Once you get the miss ironed out a good carbon cleaner is your right foot and some straight line pavement

If it is an older motor maybe the water in the fuel cleaned the cumbustion chamber enough to knock off a piece of cardon and stick a valve. This happened to mine.

I had a terrible miss in the truck after I put it back together and I thought I was gonna have to tear it down and redo the timing. No matter what I did, new plugs, cap, rotor wires etc.... nothing helped. I tried a little dielectric grease on the plugs, wires and cap and its gone. 3mos. and no miss. Its just a cheap ass suggestion.

Seth, when you rebuilt the carb did you replace the powervalve by chance? if the engine ever backfired through the the carb it may have blown it.

What kind of carb are you running?

I just replaced it this last time I rebuilt it. I've rebuilt this carb a couple of times now with all new parts.

Noook I tried the smaller gap on the plugs. No difference. I got a hold of the pressure tester last night, every cylinder is within a few PSI of the others. Cap and rotor looks fine. Its brand new (2k miles) as well.




Stock. All I can get away with here.

[quote="Twisted Minis"]Noook I tried the smaller gap on the plugs. No difference. I got a hold of the pressure tester last night, every cylinder is within a few PSI of the others. Cap and rotor looks fine. Its brand new (2k miles) as well.


OK, well on to something else, you have good compression, its getting fuel cause it does run, and air it should have, all you need to run, air, fuel, and spark. You might try while its running pulling plug wires off the plug one at a time and see if its actually sparking at each one, use some insulated handle pliers unless you like getting bit. If all are sparking then its gotta be a plug gone bad or something internal causing it, if no spark or a weak spark the wire or cap could be the culprit even though they may look good.
If all the small checks test OK then possibly a leak at the intake manifold on the dead cylinder, sucking air leaning it out to the point it won't run right, another possibility could be a flat cam lobe, the valve won't be opening to ingest air fuel, but will still give a good compression reading because its closed. The cylinder thats missing is either not getting fuel into it to fire or its not getting spark to it to light it off, lunch is over and its back to work, but I'll keep thinking and let you know if I come up with something else. Laterz

I did a similar spark test. What I did was pull the plug wire while it is not running, and ground it, then start the truck and see if it makes a difference in the way it runs. It made a big difference when I pulled 1 and 4. A small difference on 3, and no noticeable difference when I pulled 2.

I did notice, when I attached a plug to the pulled wire, it had a weak spark. But when I grounded it with a screwdriver it would throw a very powerful spark. I never tried this with the AutoLites, just the used NGK plugs.