Attached are two photos of plugs that indicate problems, but I don't know enough to diagnose it. Lately the engine has been a problem maintaining cruise at 4800 rpms. Running 18 miles to the sword grounds it works fine, but on the return trip full throttle will get only up to 4400 rpms.
The plugs are NGK ZFR7F with 50 hrs on them.
The first plug (No.1 on the engine) has a black streak on the porcelain under the center electrode.
The second (No. 3 on the engine) seems to have excessive tan deposits on the porcelain under the center electrode.
The other two plugs in the engine look normal.
When examining the plugs I did a compression test, too, with the following psi results: 140, 136, 140, 141.
Any ideas about the wear patterns on the plugs?
The plugs are NGK ZFR7F with 50 hrs on them.
The first plug (No.1 on the engine) has a black streak on the porcelain under the center electrode.
The second (No. 3 on the engine) seems to have excessive tan deposits on the porcelain under the center electrode.
The other two plugs in the engine look normal.
When examining the plugs I did a compression test, too, with the following psi results: 140, 136, 140, 141.
Any ideas about the wear patterns on the plugs?