2U pumps

Hi 22B,
purely of the top of my head after looking--NPR would give relevant Service Magazine articles relating to your query.

First would be change from Castellated Nut holding the Tall older unit together on to the later Forged body pumps with a bleed screw.

Later Forged Body pumps without bleed screw.

Somewhere in there would be a quiet idle cut on the Low Idle side of the Plunger Helix dump channel, see scan below from a Service Magazine Dated :- June 20 1949 on the D397 engines.
Articles I found told of the Pusher D8 having a fuel system with characteristics of the units used on the D386 engine which are the predecessors of the D397 units.

I feel I read about this quiet idle cut that may have first been applied to D2 type engines for a more stable Low Idle and seem to have spread across the range.
I will keep looking for more on this.

Changes beyond these to the 1P numbers I am not personally aware of--someone else or said Serv. Mag. articles or such from the NPR supersessions may tell more and if said 1P units, or indeed any of the other P/No units, need to be installed as a full set or not to save rough running at lower or other speeds.

I stand to be corrected.

Cheers,
Eddie B.

[quote="edb"]
I feel I read about this quiet idle cut that may have first been applied to D2 type engines for a more stable Low Idle and seem to have spread across the range.
I will keep looking for more on this.

Cheers,
Eddie B.[/quote]

Hi Eddie,
Not wanting to "hijack" this thread, but what you say Eddie regarding the more stable idle on the D2 engine rang some bells for me. I heard a long time ago that some of the early D2s broke the crankshaft when idling. If this were true then would this "quiet idle cut" have been the solution to that problem ?