So Keith here sent me his reproduction BK/BJ's to check out for him. He says they weren't running right. I have been wanting to look at these for some time to compare them to the originals.
At this point I have restored roughly 25-30 sets of BK/BJ's, and rebuilt or tested many others, so I feel I have a pretty good idea of the calibration and what they are all about.
In the past I had only seen pictures of the repros, obviously the plating colors are not correct, and certain things like the main body casting, the VS top castings, and the bowls are not like the original. This is understandable as I doubt Holley would remake dies for a very old carburetor like this.
What amazed me was what follows:
List number 2804/2805
Date none
Type 4160
Primary
Float side hung nitrophyl
Booster .120 Straight leg
Angle Channel .118
Pump nozzle .025
Pump type and cam 30cc white#1
Idle air bleed .070
High speed bleed .034
Metering block# none
Main Jet 60
Power valve 6.5
PVCR .030
Emulsion 2 @ .028
Kill Bleed .027 to nonexistant emulsion tube (will plug)
Idle Feed restriction .027
Mixture screw hole .062 one side, .063 the other
Needle and seat .097
Venturi size 1 3/16, 1 1/4
Throttle plate size 1.5 107/116
Secondary
Spring color Stiff plain
Diapghram length 2.2
Float side hung nitrophyl
Booster .120
Angle Channel .118
Pump Nozzle na
Pump type and cam na
Idle air bleed .027
High speed bleed .034
Metering block/plate# #6plate
Idle Feed Restriction .031
Jet size .067
Secondary leak hole .021
Needle and seat .097
Notes:
1. Floats set WAY too low indictating high fuel pressure or bad sealing needles.
2. Both Primary Throttle plates very uneven on transition slot, one was .020 off and the other carburetor was .010 off
3. Secondary throttle plate adjuster changed from flat head to allen head set screw for easier adjustability
4. Bowl vent whistle installed incorrectly resulting in the whistle being loose in the bowl.
5. Idle mixture screws out 1.75 turns and cork gaskets not fully seated. My experience with carbs of this size, 3/4-1 turn out is where they normally end up.
6. Neither vacuum secondary pot will open while dry testing on the bench. Changed both springs to lighter ones, both open on the bench.
7. Emulsion tube feed drilled, but no emulsion tube. will plug with 4-40 set screw, this will often delay initial main flow and cause instability once flow is initiated, this is normally noticed as a light surge at cruise.
8. Secondary carb, primary throttle closed too far, primary carb/primary throttle open too much.
9. Primary Idle air bleeds on primary carb both .070, secondary carb had two different ones, .070 and .061
10. Very bad casting flash at vena contracta
11. High speed air bleed is excessive at .003-.006 too large
12. With the exception of the High Speed air bleeds, these are an exact replica of an 1849 or a C3AE-9510-C, NOT BK/BJ carburetors. The original carburetors were 600cfm each, these are realistically closer to 525-550cfm each.
Emulsion feed hole:
IMG_1640 by
Drew Pojedinec, on Flickr
Float level when dissembled:
IMG_1639 by
Drew Pojedinec, on Flickr
When the float is set this low to counter higher fuel pressure it does seal at idle tho blowing past the needle is a greater possibility.
Also when WOT happens, the fuel level in the bowls drops, the needle tries to refill the bowl to the proper level, with high fuel pressure the float cannot drop very much as it is already low, this picture is the float at full drop when running 6.5psi of fuel pressure, Keith's carbs were set higher still:
58779054_453691662036237_1750090549102116864_n by
Drew Pojedinec, on Flickr
With 4-5psi of fuel pressure, the float can seal the needle at a much higher level as not as much force is required to shut off the lower fuel pressure. At full drop the needle and seat looks like this:
58577549_453691675369569_7572358759704428544_n by
Drew Pojedinec, on Flickr
Obviously it is much more open and less restricted. Typically with high fuel pressure the engine may run alright at idle and off idle, but when heavy throttle is applied the carburetor runs out of fuel.
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