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Talk about engine building here. New products, tricky questions or showcase your work - If it's engine building related it's welcome here.
When doing our initial tunes and cold start tuning, we are seeing the plugs getting fouled pretty easily. To clear this, we remove the plugs and then clean them by heating them with a propane torch to burn the carbon off the tip and insulator. This leads to a few questions as we are seeing some issues:
1) Does anyone else use the "propane torch" method of cleaning plugs? It was passed to us verbally and we don't know if there is a proper procedure or downside to doing this. How hot should one go?
2) We are seeing some plugs failing due to high resistance or open circuit on the tip. Could this be a result of our cleaning method?
3) We measured a brand new set of Autolite APP3926 plugs and found the resistance to be between 5k and 8.5K. The inner-webs are saying anything over 5K is bad. What should we expect as resistance and at what point is it too high
I'd imagine the vast majority of users here would be on NGK or Denso plugs. I don't think Autolite have a particularly good reputation.
1/ I soak the 'plugs in carb' cleaner and use old toothbrushes to scrub them. DO NOT use any sort of metallic brush as they can leave metal residue that may lead to tracking under load. As an apprentice we used an abrasive cleaner for spark plugs, I wouldn't do it now because of the risk of carbide being trapped and later dropping between the piston and cylinder wall.
2/ Some spark plugs are made with an internal air gap, don't think it applies here though. It could be down to the 'cleaning' method, try keeping a record of the new resistances, used, cleaned, etc. for each to see it there's a pattern.
3/ Depends - if using coil-on-plug the coil manufacturers/suppliers may have a figure, if using leads I'd be more concerned about the overal resistance including the HT leads. Where the good/no good line lies I can't say, as I haven't run anything that was that finely balanced on the ignition side.
If you're running into this issue during the initial start and cold setups, the simple answer it to use spark plugs a couple of heat ranges hotter/softer, or the OEM spec' plugs for the engine. They should be more resistant to fouling and you aren't loading the engine which would overheat them. Then when you have the cold/ low rpm/load sorted out, so it runs cleanly down there, you can put the correct grade plugs in and start the load mapping.
IIRC, Autolite is the 'in house' Ford brand, and will probably have been made in the same factory as other brands, but may have slightly different design and di-electric properties. Doesn't mean they're 'bad', but might be worth trying different designs, brands or heat ranges - on that last, there is often an overlap between brands and you may find something that's a half heat range warmer that might help..