Originally Posted by dhpro

When this happened to me it was a leaky manifold gasket. I did all the same trouble shooting ur doing and pinned my crank (good idea anyway). U can try using a smoke pencil around the manifold and see if u notice anything. Have u had the unit off recently? Check the torque on the bolts first as if they're loose that cud be all/part of the prob. Talk to Brian @ Mag or Joe at Left Coast. R/
PS...if u end up takin it off to check the gasket, prob worth while to send it back to mag for an overhaul after 40k miles. R/