How To Improve Six-Cylinder Performance
Make The Most Of Your Inline Mustang's Potential
There are some variations in the 1100 you need to know about aside from venturi size. From '63 through '67, the 1100 carburetor (except '66-'67 California emissions) had a spark control valve (which looks like a Holley or Autolite power valve). Its purpose is to switch between intake manifold vacuum (constant) and venturi vacuum (throttle controlled) for the Load-O-Matic distributor, which does not have a mechanical (centrifugal) advance. Instead, the spark control valve applies throttled vacuum to the vacuum advance as the accelerator is pressed and rpm increases.
For '68-'69, as well as California emissions vehicles in '66-'67, the 1100 carburetor took on significant changes, including a 1.10-inch venturi in all 170 and 200ci applications. The spark control valve went away because there was a new Autolite single-point distributor with both mechanical and vacuum advance.
The 1100's automatic choke system is identical to what we find on the 2100 and 4100 V-8 carburetors with a choke heat coil and hot air manifold heat system. Hot exhaust manifold heat is drawn to the thermostatic coil, which expands with heat and pulls the choke off. A choke unloader speeds up the pull-off process to both reduce emissions and save fuel. If the automatic choke is set too lean, you will experience hesitation and stalling. The key is to adjust the automatic choke for just the right amount of choke and pull-off.
Hesitation at operating temperature usually comes from accelerator pump issues. The accelerator pump injects raw fuel into the venturi to help close the lean gap between the idle circuit and power circuit when you step on the gas. If the accelerator pump shot is insufficient, the engine will experience a temporary lean condition and hesitate. The accelerator pump's purpose is to keep the fire lit during that transition from idle to power circuit as you get underway. Autolite 1100 series carburetors are notorious for hesitation due to an inadequate accelerator pump shot and/or poor choke adjustment. It's really about proper carburetor adjustment more than anything else.
If an 1100 is adjusted properly, all you need is a 3/4 step on the accelerator pedal prior to start-up. This puts raw fuel in the carburetor throat and activates the automatic choke if the engine is cold. If it is at operating temperature and the choke is open, the raw fuel shot will aid starting. There is no need to goose the throttle on start-up. Step on the gas once prior to start-up and the engine should fire right up if everything is in proper working order.
Ford's Load-O-Matic single-point distributor is a six-cylinder exclusive because it is different than the dual-advance distributors used on Ford V-8s. Dual-advance distributors, as the name implies, have both vacuum and mechanical advance. The six-cylinder Load-O-Matic distributor doesn't have a mechanical advance. Instead, the spark control valve channels intake manifold vacuum depending upon driver input. This is unique to '63-'67 49-state 144/170/200ci sixes, which includes most six-cylinder Mustangs out there. Where it becomes different is '66-'67 California emissions and '68-'69 49-state where Ford fit the 170/200ci sixes with a more conventional dual-advance distributor, eliminating the spark control valve and Load-O-Matic distributor entirely.