As Don mentioned, there is also an oil "trap" located under the intake manifold to which the flame trap lines ( at least one anyway) run. This can get plugged up on neglected engines but I'd tend to doubt it if your oil has been changed on schedule. I haven't messed with the one on our 850 but I did flush the one on our old 740 a time or two as it is much easier to get to. The procedure was pretty simple on the 740 in that you'd remove the flame trap and install a long funnel in the holder and dump half a bottle of GUNK Motor Flush down thru the trap. You'd do it during an oil change when the plug was out and the GUNK should go right thru and out the drain hole in the pan if it's open. If the trap is plugged, the solvent would dissolve the crud at least in theory. I'm guessing this could be done on the 850 as well with a little more difficulty.

bl