Thoughts on spark plugs fowling?

[willem445]

So my truck runs really good for quite a while but every once in a while it starts running like crap. Usually either replacing the plugs or cleaning them up with a wire brush fixes it. This is happened 3-4 times now and I have barely put any miles on it. Just driving it around the farm every once in a while when I go home. Any thoughts on what would cause this? The last time it happened it ran great the day before and the next day it sounded like a cylinder was missing. I replaced the plugs and wires and it ran great again. Im using the AC Delco R45TS plugs each time. Would a different plug make a difference?

The plugs are all gaped correctly and there is no physical damage to them. Just a blackish coating on them. To me they look more carbon fouled than oil fouled. I dont have any pictures at the moment but I will be going home friday if pictures are needed. I checked compression a while back and the results can be seen below.

[hatzie]

Fluffy black carbon fouling causes misfiring. It means you are running too rich.
Delco R45T or R45TS are the correct heat range plug to be running.
The choke might not be opening all the way or the carb is malfunctioning from crud causing it to dump in more fuel than it should.

Your compression numbers aren't far apart. They are a little low tho.

Compression ratio vs compression gauge PSI on a 350 Smallblock

8:1~8.5:1 140-170 psi
8.5:1~9.5:1 170-210 psi
9.5:1~11.5:1 210-275 psi
11.5:1 & higher 250+ psi depending on cam and other variables


Your cylinder #s are not correct on your sketch.
One head is Even # Cylinders and the other is ODD #.
---------
Rear of engine (to the firewall)

8<--->7
6<--->5
4<--->3
2<--->1

Front of engine (to the radiator)
--------

[Dead Parrot]

If the only running around is on the farm, it is likely it isn't getting warm enough to fully open the choke and never recovers from the way rich condition the choke causes. Use it to run an errand to the co-op once in a while and your problem may go away. It takes these trucks 5-10 miles to get fully warmed up.

If it isn't going to leave the farm much, might try running a hotter plug.

[homemade87]

Does it smoke out the exhaust when you first start it cold . If it does you may also be getting oil from the valve seals and adding to the problem .

[willem445]

Originally Posted by Dead Parrot

If the only running around is on the farm, it is likely it isn't getting warm enough to fully open the choke and never recovers from the way rich condition the choke causes. Use it to run an errand to the co-op once in a while and your problem may go away. It takes these trucks 5-10 miles to get fully warmed up.

If it isn't going to leave the farm much, might try running a hotter plug.

This make sense. I have been working on it alot so its mainly been starting it up for short periods of time and it really hasnt gotten to warm up fully. I am in the process of making it street legal so hopefully longer trips will be a possibility soon.

[motornut]

If the choke is vac/operated a vac leak would/could leave it on.
I've had to tie off some,rough to start, but sometimes can help sort it out

[willem445]

Originally Posted by hatzie

Fluffy black carbon fouling causes misfiring. It means you are running too rich.
Delco R45T or R45TS are the correct heat range plug to be running.
The choke might not be opening all the way or the carb is malfunctioning from crud causing it to dump in more fuel than it should.

Your compression numbers aren't far apart. They are a little low tho.

Compression ratio vs compression gauge PSI on a 350 Smallblock

8:1~8.5:1 140-170 psi
8.5:1~9.5:1 170-210 psi
9.5:1~11.5:1 210-275 psi
11.5:1 & higher 250+ psi depending on cam and other variables


Your cylinder #s are not correct on your sketch.
One head is Even # Cylinders and the other is ODD #.
---------
Rear of engine (to the firewall)

8<--->7
6<--->5
4<--->3
2<--->1

Front of engine (to the radiator)
--------

Thanks for the reply. I do understand the firing order of cylinders, I just labeled the cylinders and spark plug wires in consecutive order for ease.