Strange the way this discussion has progressed...from "only carbs with sight plugs are true GMC" to "maybe there was one without"
Retro-roco wrote,
"....The first is 2135998, CARBURETOR ASSY. (Zenith 9778). It neither shows, nor lists the Sight Plug. The parts diagram is very similar (virtually identical) to the diagram you posted above from Parts Manual, TM10-1562 , 1 May 1943. The only differences that I note are the lack of a sight plug; and the throttle plate and shaft are rotate about the shaft 180 degrees (ie the shaft lever points down, NOT up. Now where listed is 2196082 Plug Sight Level.....the second carb listed is 213747, CARBURETOR ASSY. (Zenith Model 30 BW-11, Stock List #10046). It is noted as "NOTE: Following Carburetor not Used at Time of Publication." No where listed is the sight plug, GM-2178496.....
OK....let me make a little correction if I may.....
But first...You guys are using only half the numbers.....
GM part numbers are nice but you must use both numbers...GM and ORD. You will see in a minute why.....
Now..... the GM# 2135998 carb is not the first but the second....and the GM# 2137474 (cast iron) is the third.
The GM# 2103965 carb is the earlier one which was then superceded by the GM# 2135998.
Now, as I said......one should use both numbers when referring to parts because this may make a huge difference and tell a story.
Let's look at these carbs again with both numbers.
GM# 2103965 .........FSN # G 508-7002790
GM# 2135998 .........FSN # G 501-0131595
See what I mean? The FSN tells the tale here.
G-501 is , of course, a DUKW......and even though Paul thinks DUKW discussions don't relate to CCKW's..... this, as most engine changes do...does!
So the carb with the sight plug was developed for the DUKW..that's why it has a G-501 prefix.The ORD 9 for the G-501 notes that this carb used on " Chassis prior to 5900..." .... so this means from DUKW Chassis number 001 to 5899 this carb was used.
The parts listing and illustration clearly show the sight plug. The parts list also notes " This part is also used on Truck, 2-1/2 ton, 6 x 6 (GMC) (SNL G-508)
So ..if we want to date when the # 213998 die cast carb with sight plug was first used we must check the GMC documents on the DUKW production.
DUKW # 001 , motor # 270-121725 was the first DUKW but # 006 was the start of volume production so I would go with that date .....12/2/43.
This is when the die cast carb with sight plug started in motor production.
Jim Gilmore
Jim Thorpe, PA.