fouled spark plug
Thread Starter
Cruising
Joined: Aug 2005
Posts: 11
Likes: 0
From: Arkansas
fouled spark plug
As you may have read in my other thread I just bought a '77 and am trying to some things that are wrong with it. It developed a frequent miss so I changed the plugs. All of them looked fine except for the #8 plug which had some flaky, sooty material caked on it. It ran fine for about 15 minuted then the miss started to come back. I'm thinking it might be a valve seal or maybe head gasket, what do you guys think?
thanks, Daniel
thanks, Daniel
Race Director
Joined: Sep 1999
Posts: 11,360
Likes: 382
From: Plano TX
Dry, flat looking back stuff or shiny? Dry stuff would indicate incomplete burn. I take it it has a carb so I'd look at bad spark in that hole. Replace cap & rotor and plug wires.
If it's oily (shiny) there's an oil control problem on that cylinder.
If it's oily (shiny) there's an oil control problem on that cylinder.
Thread Starter
Cruising
Joined: Aug 2005
Posts: 11
Likes: 0
From: Arkansas
I just did a compresion test on that bank. results #2 120, #4 120, #6 130, #8 140. The cylinder giving me the problem has the highest comp.
The plug I took out last night had dry stuff on it but when I took it out this morning it had some wet stuff on it, none of the other plugs had anything on them.
I'm thinking it's not the rings since the comp was good right? Would a bad valve stem seal cause lack of comp too?
thanks, Daniel
The plug I took out last night had dry stuff on it but when I took it out this morning it had some wet stuff on it, none of the other plugs had anything on them.
I'm thinking it's not the rings since the comp was good right? Would a bad valve stem seal cause lack of comp too?
thanks, Daniel
Team Owner
Joined: Mar 2003
Posts: 26,118
Likes: 1,874
From: Greenville, Indiana
Originally Posted by white77vette
I just did a compresion test on that bank. results #2 120, #4 120, #6 130, #8 140. The cylinder giving me the problem has the highest comp.
The plug I took out last night had dry stuff on it but when I took it out this morning it had some wet stuff on it, none of the other plugs had anything on them.
I'm thinking it's not the rings since the comp was good right? Would a bad valve stem seal cause lack of comp too?
thanks, Daniel
The plug I took out last night had dry stuff on it but when I took it out this morning it had some wet stuff on it, none of the other plugs had anything on them.
I'm thinking it's not the rings since the comp was good right? Would a bad valve stem seal cause lack of comp too?
thanks, Daniel
Put an ohmmeter on the wire on the suspect cylinder. It may be bad. If you don't have a meter, switch spark wires on that cylinder with one from another cylinder and see if your symptoms also move. Also check inside your distributor cap for carbon tracking between the terminals.
Race Director
Joined: Sep 1999
Posts: 11,360
Likes: 382
From: Plano TX
If the problem has been there for a while you could have soot buildup in the cylinder which will increase compression.
An ok result on a compression test doesn't mean the rings are OK. A leakdown test is a much better indicator.
An ok result on a compression test doesn't mean the rings are OK. A leakdown test is a much better indicator.
