ORIGINAL: Pat Roy
If a Dubro stopper is black, it's not gas compatible. Sullivan has or had a black stopper alledged to be gas compatible but it in fact was most definately not. That particular stopper cost a bank full of money in lost aircraft before the problem was discovered.
Correct all my DuBro stopers are red(or brown). The black one came with an Chinise Yak 50cc gas plane but I don't trust it and want to be sure.