Carbs GX-1 and GX-4

[danf19]

I am wondering what a GX-4 carb was used on. They are very similar to a GX-1 which I know was used on the Harley singles.
Also, what else was a GX-1 used on ??
thanks
Dan

[T. Cotten]

Dan!

The best, so far, listing is as follows:


* * *

GX Carburetor Model Identification & Specs for American Motorcycles

Flange Type: 2 point flange and clamp type (Indian)

Harley Davidson
1926-28 Single GX-1 1 3/4 n/a #71 #50 n/a

Indian Prince
1926 21" GX-2 1 3/4 n/a #71 #50 n/a

Cleveland
1926 GX-3 1 11/16 n/a #71 #50 n/a

Harley Davidson
1926-28 OHV 1cyl GX-4 1 1-1 1/16 n/a #71 #50 n/a

Indian Prince
1926 Sport GX-5 1 7/8 n/a #71 #50 n/a

Cleveland
1926-27 GX-6 1 9/16 n/a #71 #50 n/a

Cleveland
1926 Four 45" GX-7 1 11/16 n/a #71 #50 n/a
Indian Prince

1927 21" GX-8 1 15/16 n/a #71 #50 n/a
Harley Davidson

1927-28 Single GX-9 1 11/16 n/a #71 #50 n/a
Indian Prince

1928 21" GX-11 1 7/8 n/a #71 #50 n/a

* * *

There were significant differences between the GX-1 and and the GX-4, such as a slide venturi for the GX-4, and the GX-1 had a short chokeshaft with no friction spring, but a soldered disc.

Nobody seems to know for certain,

....Cotten
PS: Info copped from http://www.indianmotorbikes.com/, which may or may not still exist.

[Steve Slocombe]

I've got two 1930 Harley C model 500 cc singles here. The one with the low serial number has a GX-1 carburettor and the higher serial number example has a GX-4. I don't know if either is original so this probably does not add greatly to our store of knowledge. Cotten's table is probably from the 1928 Schebler manual, so does not mean those model carbs were not used after that date. It looks like the $10 model GX-1 was used on the side valve 350 cc singles while the $12 GX-4 with the variable venturi was used on the 350 cc overhead valve models. As the 500 cc single was introduced in 1929 it is not clear which carb was used, but I can report that both fit. Both are 1" nominal with a two point horizontal flange fixing.

[2camtom]

Well, I've got a 1930 500 serial number 1081 and it has a GX-4. By the way it started its life with 5 years in the Danish Army.

[T. Cotten]

Uh oh, Folks!

Now that I compare the Indianmotorbikes.com chart with my own bench notes, I find some obvious confusions.
So here is a clarifiied, although conjured revision, subject to more conjuring as we go:

(GX Carburetor Model Identification & Specs for American Motorcycles)

Harley Davidson
1926-28 Single GX-1 3/4" venturi idle holes:#71 #50 11º disc Flange mount

Indian Prince
1926 21" GX-2 3/4" venturi Idle plug #1 or idle holes:#71 #50 11º disc Spigot mount

Cleveland
1926 GX-3 5/8" venturi idle holes:#71 #50 11º disc Flange mount

Harley Davidson
1926-28 OHV 1cyl GX-4 1 1/16" bore with variable venturi idle holes:#71 #50 9º? disc Flange mount

Indian Prince
1926 Sport GX-5 7/8" venturi idle holes:#71 #50 11º? disc Spigot mount

Cleveland
1926-27 GX-6 9/16" venturi idle holes:#71 #50 11º? disc Flange mount

Cleveland
1926 Four 45" GX-7 11/16" venturi idle holes:#71 #50 11º? disc Flange mount

Indian Prince
1927 21" GX-8 15/16" venturi idle holes:#71 #50 11º? disc Spigot mount

Harley Davidson
1927-28 Single GX-9 1 1/16" bore with variable venturi idle holes:#71 #50 9º? disc flange mount

Indian Prince
1928 21" GX-11 13/16" venturi idle holes:#71 #50 11º disc Spigot mount


It must be noted that many of the disc angles are guesses. The Service Station Manual lists "P-478" for most models, but the GX-4 is unique with a "P-705".
Although 9º has been found in GX-4s, it will not cross between the idle bleeds!
And the P-478 is listed for several DLX models that seem to vary in degree greatly, anywhere from seven to fourteen by the time they made it to me.
Can we come up with a consensus for that one? Eleven would seem contrary.

And note the GX-2 currently on my bench has an idle plug instead of holes. The Service Station Manual shows an idle plug for the variable venturi style, but all across my benches had the two idle holes. It also shows only the chokeshaft design using a friction spring, whereas two GX-1s across my benches were short shafts with soldered discs.

The GX-11 is listed to have a 13"/16" venturi, however the one currently on my benches is 7/8";
One of three GX-1s has been over-bored as well!

Most of the models listed have never crossed my benches.
What do you fellows find in yours?
Thanks in advance,

....Cotten