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Mc BDC-16 Carb Mysteries Revealed!
#1

.pdf   Walbro_patent_3738623_fuel-pump-leaf_1971.pdf (Size: 327.77 KB / Downloads: 16)
Ever take apart a BDC-16 (Mc101A/A) kart carb and wonder why Walbro went to the trouble of using FOUR pumper plates, even though several of the passages and chambers in those plates aren't even connected to anything??  Walbro patent 3,738,623 from 1971 explains why.

The inventor was Charles H. Tuckey, whose name seems to be on all of the Walbro patents from that era.

Anyway, the so-called "double-pumper" aspect of the BDC-16 probably isn't what most of us thought.

I haven't read it thoroughly yet, but here's what I got so far.
The patent claims a novel fuel pump spring (described in later snowmobile carb diagrams as the "leaf").  Surprisingly, the write-up goes on to explain pretty much everything else about the carb... maybe to bulk it up a bit?  No matter, it's all helpful.

The patent clearly pertains to Walbro's WD / WDA / WDA-1 / WR series used on snowmobiles, but the BDC-16 is nearly identical.  Compared to the BDC-16, the sled carbs add the "leaf," plus three tiny springs on the fuel pump check valves and (spoiler alert) the 2nd pump.  The sled carbs didn't need the BDC-16's duckbill circuit, since its purpose was to compensate for the carb being grossly oversized for the 125cc Mc101A/A (and especially the 100cc Mc9X's).

No doubt all of this will be "old news" to some of you, but I thought it was interesting.

Now... if I could only get my BDC-16's to actually WORK...

By the way, for those sled carbs, this thread is super helpful: https://vintagesleds.com/bs/index.php/to...980.0.html

Sadly, the pics aren't there anymore... fortunately, while you guys were out running your karts and generally enjoying life, I was holed-up, making a PDF.  It's too big to attach (13MB).  PM me with your e-mail address if interested.
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#2
Photo 
Doug,

Thanks for posting the material on the WDA carb patent application. One thing that I would like to share that may not be completely apparent is the reason for the conical springs. We are used to looking at carbs that have pulse passages that connect the pump systems in our carbs directly to the crankcase so the system sees alternating positive and negative pressure pulses. The alternating pressures cause the pump membrane to move back and forth in very small deflections in synch with the movement of the piston in the engine. In some applications the WDA carbs were fitted to engines where the pulse source is upstream of the reed cage so the pump system will only get alternating negative and nuetral signals. In the absence of the positive pressure pulse the carb is fitted with the conical spring and the pump membrane is drawn toward the spring by negative pressure and pushed back by the increased tension in the spring thus mirroring the movement of the membrane produced when the system is tied to the case.
Here's a link to some sample photos of the actual parts from the single pump version....  https://www.dropbox.com/sh/odx9zk6bb4v78...LVTVa?dl=0
Steve O'Hara
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#3
Steve (or anyone else), I'm curious.  Have you ever tried running a "fuel pump leaf" on a kart?  The last time I bought kits from https://www.mfgsupply.com/ I bought one, but haven't tried it.  The patent write-up refers to it as a "spring"... uh-huh, when was the last time you saw a spring made from aluminum?  I'm guessing that it's just a blocker to limit the travel of the pump skin, but they couldn't get a patent for thatBig Grin   Nonetheless, maybe it does something useful?

Ditto for the 3 tiny springs on the pump check valves.

I'm including pics from the sled write-up, with props to the author, wankel303, whoever he may be!


Attached Files
.jpg   WDA1a.jpg (Size: 67.39 KB / Downloads: 21)
.jpg   WDA2.jpg (Size: 93.09 KB / Downloads: 19)
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#4
Hi Guys have been using Mac carbs since Batavia July 7 2002 We use on our single and our twins. The new fuels are different GAS and can eat away at duck bill we use a part off a Tillotson carb part # 363-503 drill an 1/8 hole in bottom and use a gas line in duck bill hole, put in ball side up. check if gas line hardens after a few events if loose replace fuel line, some of the new rubber duck bill are fine, use fuel filter and safety wire, Were having our thanksgiving up here in Ontario and ONE of the things Shawn and myself are thankful of is VINTAGE KARTING, Richie .
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#5
(10-15-2019, 10:29 AM)richard Engel Wrote: Hi Guys have been using Mac carbs since Batavia July 7 2002 We  use on our single and our twins. The new fuels are different GAS and can eat away at duck bill we use a part off a Tillotson carb part # 363-503  drill an 1/8 hole in bottom and use a gas line in duck bill hole, put in ball side up. check if gas line hardens after a few events if loose replace fuel line, some of the new rubber duck bill are fine, use fuel filter and safety wire,   Were having our thanksgiving up here in Ontario and ONE of the things Shawn and myself are thankful of is VINTAGE KARTING,  Richie .

Hey Rich;

I sent you a PM.

Bob
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#6
Hi Bob cannot open The PM sorry Richie E-Mail rtengel@hotmail.com
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#7
Sorry Bob rtengel55@hotmail.com
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