My #5 plug_what's up with it?

[lurtch]

Hello All,

The photos show my plug set after about 100 miles of freeway driving. There was a misfire perhaps three of four times on the freeway jaunt.

They are all Bosch WR8DC gapped at .032. The ignition is conventional points but with a Pertronics high energy coil. Static timing is set at about 4 deg before TDC. The engine runs very strong and starts immediately.

What would make number 5 plug so obviously different from the others?

If the #5 exhaust valve has some blow-by would that lean out that cylinder a little?

Should I adjust to get the other cylinders to burn a little leaner, or leave it alone until after the compression check and valve clearance check?

Pertinent information: This is a newly re-machined Metric Motors engine. The FI pump is freshly overhauled, but from a different donor engine. The linkages are set up per Joe Alexanders linkage tour graphic. On first start-up it was running way too rich, but after removing one BC shim it immediately ran and idled better. It currently has about 500 mies on it.

Larry in CA

[Benz Dr.]

I think you have several issues so I'll go through them one at a time:

wrong spark plugs
low voltage at the spark plugs
possible vacuum leak at number 5 spark plug
faulty fuel injector
not enough ignition advance

When you had the pump rebuilt did you have the CSV and injectors cleaned? A lot of owners skip this important step.
You need non resistor spark plugs like NGK BP5ES non resistor type.
Are your plug wires all steel core - no carbon?
I'm running about 8 degrees BTDC - 4 really isn't enough but you will have to expiriment.
You could have a vacuum leak at no. 5 cylinder. It's very lean compared to the others which are on the rich side.
If you have a hotter coil you could probably open the spark plug gap up to .034
The other plugs are a bit rich but that's OK for engine break in. The pump could still be running a bit rich but you would want to fix the lean cylinder first before moving on. Any leaner and you could start to do damage to the piston or score the cylinder walls.
Best to check the valve lash and compression before moving on. If you haven't completed a torque check on the head screws I would do that now with a slighly warmed engine. You can do it cold as well.