Re: misfiring.
 

The main reason for spark plugs made out of platinum or iridium is to lengthen the time between changes, so you see them stock on factory cars nowdays a lot. Those metals do not erode as quickly as copper and stay in service for a very long time. On our cars though, it is easy to change the plugs, so we usually just use cheap copper plugs and replace them more often. We often run colder plugs that do not clean themselves as well and we tend to run fairly rich mixtures and race gases that can quickly foul the plugs, so it's also not a big deal to throw out an $8 set of copper plugs, compared to a $30-$70 set of platinum or iridium plugs.

Re: misfiring.
 

Sara, did you ever get the plugs to stop backing themselves out?

Re: misfiring.
 

When i got my car it had platinum plugs that were so worn out they made the wires seem bad, the car only had 50K on it when i got it, so i bough tnew wires when that didnt help i checked the plugs and yep those platinum plugs eroded away to about a .125 or more gap, from what i understand patinum plugs are alos prone to causing detonation in these motors wich would wear away the plugs more quickly

Erik