If that was keeping the rave valve from opening then, in theory, you could have had the two cylinders fighting each other. That would keep the motor from making good power. I'm not saying this is your running problem, but we did find a broken part.
Those caps are only supposed to be turned in snug by hand even though they have that 10mm head on them. That cap needs to be replaced. They do make higher quality, aftermarket, aluminum caps. The OEM ones work fine as long as they are not overtightened.
Any indication as to why it failed?