Dirty or fouled plugs - full of soot?

[southcoasting]

All,
So the past couple years since I have been using my rebuilt A4, I have noticed my spark plugs are way too dirty. I thought maybe I was running too rich? I had my rpm set to about 500 which may be the problem? Could I have a bad carb that causes issues with fuel?

I will be rebuilding my carb this Winter and come Spring commission, I will be sure to set my rpm’s back to 800 minimum and set my fuel mixture to be more precise…any concerns here with how nasty they look though?

[Dave Neptune]

The fowling can be from many things. First check to see that the choke is not stuck and actually opening. Another item to check is the flame arrestor to be sure it is not clogged. Also if the exhaust is really old excessive back pressure can cause fowled plugs along with a "slowly increasing" drop in performance.

Poor ignition and timing can also contribute. Do you have a strong blue spark?

Usually problems with the carb are caused by a lack of fuel not to much unless the float is not closing properly or an air jet is plugged up causing an over rich condition.

The idle speed should have little to do with the fowling. Also the "idle air" adjusting screw only controls the idle and influences the mix to about 1200 RPM's. How many turns out is the screw at? They usually like around the 1 1/2 turns +/- 1/4 turn if all else is OK.

Dave Neptune

[southcoasting]

Originally Posted by Dave Neptune

The fowling can be from many things. First check to see that the choke is not stuck and actually opening. Another item to check is the flame arrestor to be sure it is not clogged. Also if the exhaust is really old excessive back pressure can cause fowled plugs along with a "slowly increasing" drop in performance.

Poor ignition and timing can also contribute. Do you have a strong blue spark?

Usually problems with the carb are caused by a lack of fuel not to much unless the float is not closing properly or an air jet is plugged up causing an over rich condition.

The idle speed should have little to do with the fowling. Also the "idle air" adjusting screw only controls the idle and influences the mix to about 1200 RPM's. How many turns out is the screw at? They usually like around the 1 1/2 turns +/- 1/4 turn if all else is OK.

Dave Neptune

Thanks for the information Dave. You have always provided valuable feedback and glad to see you still are.

I will be overhauling my carb this Winter and also checking my timing this coming Spring. I had just installed a new exhaust system so it sure it’s that…my exhaust manifold is a little suspect though…it has a good amount of hot spots…one thing I noticed it gummed up fuel around the top of the carb near the idle jet…