The accelerator pump !
They "lacked" another feature the other carbs had . . . now it was gone.
The float bowl.
Gravity feed fuel flow from the tank. Starting meant a few squirts, a choke, a couple kicks and it was running. A simple design, with a hell-of-a-lot-of-parts ! There's more parts to these things (just look at a parts book). I restored this one and still need the throttle cable holder metal strap deal and bolt that goes off the wood spacer block. The bolt's hex head is displaced in the drilled recess in the spacer block.
You can buy these carbs at a swap meets sometimes for about $5.00 . . . But the carb kit is about $40.
The diaphragm is the weak link. Big Noot said these things actually work pretty good, are tunable and have decent throttle response, and make power (at least on ironhead Sportsters). The carb body came standard with a "racing bombsite fuel atomizer" that you pay big bucks for if you want one now.
You ever see those "vent tubes" sticking out the bottom, right side of Sportster tanks? That tube fits a hose that vents to the top of the Tillotson fitting. You don't need to run it. I believe it was more of a gas vapor emission tube to keep it from venting to our squeaky clean atmosphere.
You ever see those "vent tubes" sticking out the bottom, right side of Sportster tanks? That tube fits a hose that vents to the top of the Tillotson fitting. You don't need to run it. I believe it was more of a gas vapor emission tube to keep it from venting to our squeaky clean atmosphere.