MTFCA Forum

I don’t know that I’ve seen this discussed here before but here are some minor differences in the body castings of the later Pat’d Dec 22, 1914 Holley G carburetors and the earlier Pats Pending carburetors and how they evolved from the 1912 H1. The 1913 Model S, while similar in design, was significantly different.
A telltale feature you can spot without disassembly is a 1/16” hole in the throat which allows gasoline from the intake manifold to drain back into the mixing chamber on the later models.(first picture)
The Pats Pending and H1 lack this feature but have a series of 6 holes drilled around the top of the area directly under the top of the jet, whereas the later models only have one hole there. (second and third pictures).
The jets for the H1 (left) and Pats Pending (center) have a keyhole slot with the H1 having a slightly differently shaped basin. The later version has only a round hole with 4 passages cross drilled towards the top. The idle pickup tubes and their fittings are slightly different as well with the H1 being round and tapered at the bottom while the Pats Pending and the later G’s use a tube flattened at the bottom and the fitting is more rounded at the screwdriver slot.(last picture).
The venturis interchange as will the throttle arms but their profile and hole spacing is a little different. Also the H1 mixing chamber covers seem to be smooth on the flat top area where the Pats Pending and later are a rough casting finish. May not can tell from the picture. Just things I’ve noticed over the years but never seen brought up.

The H1 used filister head screws with a slightly different arm design, the Pats Pending the combination hex-slotted screws that gave way to round headed screws.

Do they all perform as well?
Is this a typical simplification of unnecessary machine work/time similar to the variations the NH went thru?
The idea being to save fractions of a penny or better per unit which turns into real & noticeable profit over 100,000's to 1,000,000 plus units.

P.S. Thank you for the evolution history.

They seem to run the same. The G is just an H1 with a simplified float mechanism. I suppose they did save money on the drilling of 6 holes, but the ones without the six holes have a stand pipe about 3/32” soldered to the top of the air bleed/drain in the bottom to compensate for the extra gas that would pool there from the hole then drilled in the carburetor throat. This is absent on the H1 also.
Some G’s have a choked down hole where the inlet needle seat screws in, same as this model S, just in a different location. Most Models G and S are unrestricted there except for the oriface for the needle.

There were lots of changes to the G, the spray needles were money saving changes. The top part went from the round knurled knob, to a brass bar, to a steel bar, all 3 drilled and tapped 1/4-32 and pinned, then the last simply swaged on.
Usually the bottom of the needle seat can be seen in the inlet, but not on the restricted ones. I don’t think this affects performance because I drilled out the restriction on a model S to see and it wasn’t noticeable if any difference.

Another money saver was the float hinge. At first it was stamped brass formed and soldered to a small tube. Later it was stamped brass formed to function the same, no soldering required.

Corey, many thanks for this detail on the "G" model, my favorite carb !!
Very interesting, and valuable information.

You’re welcome. I like them as well. I made a clear mixing chamber cover one time so I could see what was going on in there. Here are some screenshots of the video. The last one it is flooding out when I pulled the choke.