@Jacob - What was the fuel tank and fuel line configuration? (1) or (2) wing tanks into a small header tank, directly with no vent lines? Vented caps? Fuel line over the door frame I presume? Sorry for the confusion, but I've never seen a small header tank on the firewall (which side?) as you describe. Or are you referring to the gascolator possibly?
@JP/ALL - I've read the SB and not 'complied'. Why? Because I have a single (right) wing tank and panel tank on my M-III, both with vented caps. The fuel line exits the wing tank to a shut-off in the head rack, across the rear carry through tube, over the pilot side door, down the vertical door post, along horizontal tubing under the dash tank, then into the fuel selector below the dash tank near the dash tank outlet fitting.
Based on wording in SB#29 (emphasis mine):"NOTE: For those operating wing tanks in conjunction with the large, front main tank, the wing tank fuel lines should route: forward from the wing tank, above the door frame work, down the diagonal bracing in the windshield area, and plumbed directly into the filler neck of the main tank. The wing tank fuel valve can be installed in the headrack above the door. Because of the capacity and fuel visibility in the main tank, the question of fuel flow stoppage from the wing tanks is not as critical. With the fuel routed into the filler neck, you will have a constant visual on all fuel."
This reads somewhat ambiguous to me, ie. when utilizing the panel tank is it applicable to single, or multiple wing tanks only? Regardless, as the SB was originally issued to remedy multiple wing tank usage issues, I question whether it is anything I need worry about. Is head pressure sufficient to keep fuel flowing even if my current routing is not continuously downhill?
In any event, I have NEVER seen fuel line routed down diagonal bracing into the filler neck. Has anyone done this? The SB recommendation for my fuel configuration seems problematic as it just dumps into the main panel tank. With the wing high, I should think the potential for in-flight overfill spillage exists if one were distracted.
I dunno, I'm inclined to leave well enough alone...