Doug,
I respect Dave Atherton and all his experience. Those Racor fuel systems that leaked air at the prefilter probably had issues with idle and surging and I am happy those issue are resolved for you and others. I have done the maintenance changes on the Racor, to keep it air free, and have none of those issues to resolve. At some point when the electric pump in my current Racor fails, I will be faced with a decision of purchasing a simple head like Cat makes or one with a purge pump system like the one that Marty shared. For now the jury is still out on my migration path...
What Dave kindly passed along while using the Cat head, was to put the filters in dry, open the bleed screw on the final filter, crank the engine 30 seconds, let starter cool (I am guessing the customary 2 minutes. Dave leaves the bleed screw open I guess, which seems strange to me), then crank again 30 seconds and engine will want to start. By the second 30 seconds you should see fuel coming out the bleed screw, it will run rough trying to push the air through, then tighten bleed screw.
We have 60 seconds of open air purge valve and no fuel supply while cranking. I'm personally OK until we get to "it will run rough trying to push the air through". I have read C12 threads (non BAC) where engines without operable fuel purge pumps have not starting after a fuel filter change. I have no idea how some ended up with an air bound C12, given I do not know what procedure they used. If there is any chance of this happening to me, I would certainly opt for a purge system built into the filter head when making the change.
This issue may be just a personal dilemma on my part, not sure. It may be resolved in time with postings by BAC members who have made the conversion to the Cat head and have been through filter purging a number of times without issues. Hopefully those folks will post their experience here. We could document the procedure on BAC ourselves in time.
The issue....I could envision Beaver owners being on the road and having a fuel problem symptom, or it is time to have a filter set change. Would every tech who does service in the field know or have Dave's procedure at hand? Would you as the owner be responsible for telling the tech how to do this? If your engine ended up air bound who would own the expense of the problem? This is my personal dilemma with not having a Cat service bulletin or procedure in hand to pass along if it is needed. I am very comfortable that I could change filters on the road with a built in fuel purge pump and that most any tech could also. I know Dave Atherton was trying to explain this procedure to other Cat techs who may have been unaware, I do not see myself trying to carry that ball without a Cat procedure in hand.
So if anyone can come up with a documented purge procedure from Cat that we can have on board, that details how you are to purge a C12 of all the air when you do not have a purge pump, I think it could just make life easier while on the road and give those of us that do our own maintenance, something written to follow.
This is just my perspective, for what it is worth, and not intended to open any big debate on Racors etc.
Dave Atherton has been a great and kind resource to many of us and he has vast knowledge. This post is about what I am comfortable with and not any question about his deep CAT knowledge.
Later Ed