Craig,
Can you comment on what and where the mixture control and throttle takes effect with the OLD and NEW fuel pump?
As I understand it, with the OLD fuel pump the throttle controlled total fuel flow through the pump but the mixture controlled what went to the spider. So therefore WOT + cut-off meant max fuel from the tanks, through the pump and back to the tanks via the vapor return. Do I have that right? Yes. Using this method for 30-40 seconds with high boost on for “older” Continentals is a GREAT way to cool the fuel system and get rid of vapor and make hot starts easy or at least MUCH better.
So what is happening with the new fuel pump?
Engine not running, mixture at “idle cut-off” and low boost pump on, I get 2-3 gph fuel flow to the engine. With high boost pump on, I get 12 gph plus fuel flow. 30 seconds makes a big mess! The really weird part is……with throttle closed, mixture full “rich” and low boost pump on, the fuel rate is nearly zero. As I slowly pull the mixture towards “idle cutoff”, the fuel rate stays at zero until about mid-mixture travel and then it increases and stays about the same all the way to idle cutoff.
Also do you know roughly when the NEW fuel pump started manufacture? No. Dave Dewell from Great Plains Fuel Metering Inc. told me….”Continental changed the mixture shaft in this style pump a while back”. Dave is VERY knowledgeable of the Continental fuel system and I highly recommend him to anybody needing fuel system service. My 2004 Bonanza (now know as the station wagon) has the new style pump as well as my IV-P.
My engine is a 1995 tsio-550B and seems to work with the WOT + cutoff method. Impossible to mistake when 12 gph flows out the sniffle valve with high boost on.