Spark plug condition?

F

finnstanger

Well-known member
My stock 200 started to run unevenly (sharp cuts) under even load. Idling was normal and I didn't feel any cuts when accelerating or running at >45mph.

I checked the spark plugs and found that they were light gray coloured,almost white. There was also quite a lot of white residue in them and in some plugs the air cap had filled and reduced.
I replaced NGKs with Motorcraft BSF82Cs and it started to run normally.

Is too lean fuel mixture causing this ?
I'm using 98 octane gasoline(91 super?) with Kalium based lead substitute.
 
If your fuel mixture was too lean, your plug tips and electrodes would show signs of overheating, such as blistered ceramic insulator and eroded nose.

Your old NGK plugs might have been a step too hot, and maybe didn´t go well with your high octane fuel. Besides, a stock 200 shouldn´t need high test... you could try regular one time and listen for knock or pinging.

The white powder residues you described were a sign for heavily leaded fuels back in the days of leaded gas; yet I don´t know if kalium leaves white residue as well.
 
After replacing the plugs I drove to Stang owners weekend and when I was returning from 700 mls long trip, engine started to act like I earlier descriped. At this point I had alredy started to use regular gas without lead substitute.

- Engine does not burn oil and oil stays clear when checked .
- Fuel economy 25mls/gal (Highway, typically 60-65 mls/h)
- Distributor: Load-o-matic with Pertronix, 12 deg idle advance
- Coil: unknown italian replacement, primary resistance 3.5 ohms
- Carburetor: Holley replacement carb (installed 10 yrs ago by former
owner)
- New Carter fuel pump.

What I found out now is that the plugs are not so grey anymore because the other side has shiney black stuff. Here's the plug no.6 which was the worst as it was last time:

plug.jpg


Any suggestions or ideas??
 
Looks a bit like oil fouling... Is it a cooler plug than the previous ones?
 
Former plugs were NGK WR5. I've tried to trace the heat range without success. I also thought that it could be burnt oil but the engine is not consuming it significantly. Former ones were a bit lighter coloured possibly because of fuel additives etc.
If the engine would burn some oil would it block the plugs after 1000 mls?
I still believe that the engine (or plugs) is running too hot and therefore I:
- checked the main jet and replaced 66 with 70.
- checked that DT-mark on the damper is OK.
- checked idle timing and adjusted it to 14 deg.

Let see what is the result.

Pete
 
The Motorcraft BSF plugs come in three heat ranges: BSF 42 C, BSF 62 C, and BSF 82 C. The 82 is the hottest of the range. The BSF42C is a direct cross for an Autolite 45. Maybe someone can take the heat ranges from there.
 
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