Just wanted to get some input on favorite spark plugs for Lycoming O290-D operators. I'm running REM 40E and seem to get some fouling. What have you had the best luck with?

I'm running REM40E champ's in my O-320-E2A. They work fine, as do Unison's (now Tempest).
Are you running avgas? Try the ethanol-free mogas over at lebanon state airport-- not sure if it's 87 or 92 octane, but even 87 oughta be OK with a 290D, although a D2 might need 92.
If carbon fouling, try leaning more. If oil fouling, you've got bigger problems.

I'm running REM38E's in my O-320. They aren't the right ones by the book, and I do have a fair amount of fouling, especially when doing aerobatics. I have 40s on order and plan to change them asap. I'd stay with the 40s, and like hotrod says, try leaning more or mixing some E-0 fuel in it.

Sent from my Galaxy Nexus using Tapatalk 2

I had an O-290d2 in a Piper J-5 that would foul plugs, switched to fine wire plugs and the problem went away. Cant remember the number but maybe the fine wire version of the one you are using.

I originally ran an old set of fine wire, and I think they worked much better, thats pretty much why I'm asking. But they are so dam expensive.