Delving into three "G" carbs, I have one with a replacement aluminum venturi, one with an original "pewter" venturi which measures the same as the new aluminum one, and a third, original venturi the opening of which tapers from 1" at the top to .7121" at the bottom. The other two measure .840"
What would be the result of reducing the throat diameter of the venturi by .1279" (as well as the angle of the taper) ?? Am I correct to assume the Venturi effect would be increased velocity ? How would this affect performance ? FWIW, the "necked down" part came from a brass-bowl carb which I presume to be an earlier version.
I have machined and tried several different size venturies. Quite honestly I found no noticible differences. I will try to find my notes on the sizing.
I found one without the bulge at the bottom. It's just like a straight pipe with a flange at the top.
Corey, thanks for that ! Adds a third variation to the venturi question. No taper in that one ? Here's my apparatus for setting float height - more about floats anon . . .
Yes, the brass bowl would be the earliest. I assume it's on a bronze body. Next would be a steel bowl on a bronze body, then a steel bowl on a cast iron body. In its few years of production the G went through several changes, and some of them seem to be simultaneous. Some have a ridge around the intake like an NH, and some don't, like the one in the picture, and I think both kinds may have been made at the same time. I'll leave it for somebody smarter than me to figure all that out.
There were 2 different Pats Pending tops, one with larger letters and one without a period after Pats. Then other variations in the brass and cast iron tops.
Comparing the original cork float (left) with the reproduction float now available (right) and a new float cut down to original size. (bottom) The new material weighs the same as cork, which is a good thing.
More differences - earlier carbs have a slender all-brass mixture needle. The needle on the top has a steel point tapered to a slightly shallower angle and swaged into the threaded brass shaft. It came out of a carb with a steel bowl.
I'm not a good scientist. Having changed the new type oversized float for original cork, the new replacement aluminum venturi for the original with a tighter throat, and the steel tipped mixture needle for the earlier all brass item, on the basis of a single four-mile test drive, I find the car performs better all around. Idle is smoother, and it seems to have better response to the throttle and more power at low speeds. ?!? With three variables in play I'll never know if only one change made the difference or if it's due to all three in play. ?!?
"the new replacement aluminum venturi for the original with a tighter throat,"
No wonder one of the posters here had said if you open up the venturi, It'll run like a scalded cat.
How the heck did you reshape the float? :-)
Duey, you're confusing me. In effect I closed down the venturi - the old original is 1/8" smaller in diameter at the bottom. ?!?
The new replacement material for the float works very easily. I just sanded one side with 100 grit paper until it was 3/8" thick, matching the old cork float, then rounded the edges to match the profile.
Here is another difference. Most only have one small hole in the body that goes from inside the bowl to inside where the jet screws in. Some have 6 small holes drilled around that area. Both of these 2 are brass and had Pats Pending tops.
You will also find that the G’s that have the single hole inside the body that Corey shows also have a single small hole drilled through the air inlet to the interior. This applies to both the bronze and the iron bodied G's.
The bronze ones with the 6 holes inside the body do not have this hole drilled in the air inlet. All of this type that I have seen seem to be 1914’s – meaning they have the disc topped mixture adjusting screw, Pats. Pend. cover plate, and brass bowl. Any other, or differing, ideas?
Thanks fellows for adding to the G carb's anatomy. Very interesting . . . to me, at least.
Sorry for the confusion I raised Rich B. Wasn't intended at all.
I am also liking the info shown here.