When Ford introduced the Mustang in April of 1964, the base powerplant was the Falcon's 170ci six with 101 horsepower and 156 lb-ft of torque. Later that year, in August, Ford updated the Mustang's engine line-up with the seven main bearing 200ci six as standard equipment. Both the 170 and 200ci sixes are well known and respected for rugged dependability. But engineering shortcomings have plagued them since the beginning. The greatest shortcoming is a lackluster induction system, which is positioned directly over a hot exhaust manifold. The Mustang six's ignition system was the old-school Ford/Holley Load-O-Matic distributor, which also offered disappointing performance.
Autolite's 1100 series one-barrel carburetor entered service in 1963 to replace the Holley 1900 series glass bowl carburetor. It was a Mustang six mainstay until '69. There were three 1100 venturi sizes: 1.00-, 1.10-, and 1.20-inches depending upon model year and application. From '63-'67, the 1100 employed a spark control valve for use with the Load-O-Matic distributor, which had vacuum advance but no mechanical advance. The absence of a mechanical advance hindered performance.
Although the spark control 1100 carburetor and Load-O-Matic distributor may seem unconventional in function, they're quite simple. The spark control valve gets its vacuum signal from two places in the carburetor throat. One is at the throat of the venturi while the other is in the bore just above the throttle plate. The spark control valve is calibrated to function at specific vacuum pressures (working against spring pressure) depending upon throttle position. At steady throttle, the spark control valve is held open by vacuum against spring pressure. What the spark control valve does next depends on engine speed, throttle position, and load. During acceleration, the vacuum signal is low enough that the spark control valve's spring pressure closes the valve and vacuum to the advance unit is cut off. Yet some vacuum at the venturi throat keeps the advance from going full spark retard.
As engine rpm catches up with throttle position, the manifold's vacuum signal acts on the spark control valve diaphragm, which opens the valve to provide a strong vacuum signal to the vacuum advance. When engine speed increases with the throttle open, manifold vacuum decreases and the spark control valve closes, preventing venturi vacuum loss due to bleed back caused by manifold vacuum at the throttle plate. This gives full spark advance at high engine speeds. By the same token, the spark control valve also has to retard spark when throttle position and load are such that too much timing could cause engine damage due to spark knock. The spark control valve has the job of spark advance and retard depending upon load and throttle position. What makes the spark control valve different than a Holley/Autolite power valve is vent holes. You will see them in the spark control valve, but not a power valve. These holes allow atmospheric pressure to act on the diaphragm while manifold vacuum acts on the inside to modulate the valve.
1 The 200ci Ford six replaced...
1 The 200ci Ford six replaced the Mustangs 170ci six in August of 1964 with 120 horsepower and 190 lb-ft of torque. In the beginning, most 170 and 200ci sixes were fitted with a draft tube instead of a PCV valve, which depended on where they were delivered.
2 Here's the 200ci six with...
2 Here's the 200ci six with Thermactor emissions, a California emissions air injection system introduced in 1966 that oxygenates the exhaust for a more complete burn and cleaner emissions.
3 The 170 and 200ci sixes...
3 The 170 and 200ci sixes struggle with a log-style intake manifold cast into the cylinder head right over a hot exhaust manifold. Aside from obvious fuel/air distribution issues and a very long roughcast manifold, heat creates its own drivability problems.
Beginning with the '68 model year, Ford switched its inline sixes to a dual-advance/retard distributor with both a vacuum and mechanical advance like V-8s of the period. Instead of a spark control valve, the Autolite 1100 carburetor provided a throttled vacuum signal instead of a valve-controlled vacuum signal. As a result of tougher emission standards, the dual-advance feature was also advance/retard, with spark advance during acceleration and retard during deceleration to reduce exhaust emissions.
The reason we've shown you both types of fuel and ignition systems is to show you what happens when you don't have a proper match. We've seen our share of mismatched carburetors and ignition systems, which cause serious drivability problems. If you run an Autolite 1100 carburetor with a spark control valve and a dual advance distributor, you won't get sufficient vacuum to operate the vacuum advance. If you run an 1100 carburetor without a spark control valve with a Load-O-Matic distributor, you will wind up with too much spark advance. If you're having drivability issues with your Mustang six, the first thing you need to check is carburetor and ignition for compatibility. During a recent visit to The Restomod Shop in Stockton, California, we witnessed a pristine '66 Mustang hardtop with 200ci six that wouldn't idle properly. It didn't take long to figure out why. It had the Load-O-Matic distributor with an 1100 carburetor void of the spark control valve. At idle, the vacuum signal was strong, causing excessive spark advance and making it impossible for this engine to idle properly. It needed the 1100 carburetor with spark control valve.
Terry Simpson of The Restomod Shop donned his troubleshooting skills and went to work on this Mustang with the installation of the correct 1100 carburetor with spark control valve. The more Terry examined this engine, the more troubling issues he found. You need to do the same in your driveway as a means to honing your own technical skills. Does the vacuum advance operate? Check this by connecting and disconnecting the vacuum line with engine at a fast idle. If rpm drops when you disconnect, you have a working vacuum advance. One cylinder at a time, disconnect each ignition wire at the distributor cap. Does rpm drop or remain the same? If speed doesn't change, you have a weak or dead cylinder. Spray carburetor cleaner around potential vacuum leak areas like the carburetor base plate and spacer. Does the engine surge? If so, you've found a vacuum leak. Pull the PCV valve and check for vacuum. At idle, you should feel suction and the engine should surge.
Is there valvetrain noise, meaning a clicking rocker arm or dry valve spring? If you can hear valvetrain operation with hydraulic lifters, something is wrong, mandating a visual inspection. There should be plenty of oil flow throughout the rocker arm assembly. Return flow should also be good. While you are tuning, check things like coolant flow through the radiator at operating temperature with the thermostat open. Examine the engine for oil and coolant leaks. Replace fuel hoses at every tune-up and use high-pressure fuel injection hose throughout, which is resistant to today's harsh fuel additives.
4 Expect to see two basic...
4 Expect to see two basic types of Autolite 1100 carburetors, although there are many variations of each. This is the 1100 with spark control valve, which is modulated by throttled vacuum like a Holley/Autolite power valve. Only instead of controlling fuel flow, it controls vacuum to the Load-O-Matic distributor.
5 This is the spark control...
5 This is the spark control valve on another Autolite 1100. It modulates manifold vacuum to the Load-O-Matic distributor based on throttle position and load. The 1100 with spark control valve is compatible only with the Load-O-Matic distributor.
6 The Load-O-Matic distributor...
6 The Load-O-Matic distributor is vacuum advance only and works based on throttled manifold vacuum (throttle position and load). The breaker plate is moved by vacuum and calibrated spring tension. Vacuum advance works against spring tension to advance spark based on throttle position and load. Calibration happens via the use of different spring tensions. Like most Autolite/Motorcraft factory distributors, there's one bushing and a barber pole shaft designed to bring engine oil to the shaft and bushing.
7 This is the Autolite 1100...
7 This is the Autolite 1100 carburetor without spark control valve, although you'll find an unmachined provision in the casting.
8 This Ford illustration...
8 This Ford illustration shows the '68 dual advance/retard distributor, which operates in a conventional fashion with a throttled vacuum signal. Beginning in '68, Ford also went to a vacuum advance/retard system to reduce emissions. Spark is retarded during deceleration to reduce exhaust emissions, yet advanced during acceleration for power.
9 Check the carburetor base...
9 Check the carburetor base plate with a straightedge. Warping, though not always noticeable, causes vacuum leaks. Spray carburetor cleaner around the base plate and spacer. Does the engine surge? If so, you have a vacuum leak. Have you looked at the idle air adjustment needle? Technicians sometimes tighten them too much, mashing the tip and rendering it useless.
Sometimes, we get so caught up in the confusion of engine troubleshooting that we miss important details. We swap carburetors, change ignition points, adjust timing--yet fail to notice the obvious. What about proper choke adjustment when the engine is cold, with a steady pull-off as the engine warms? Is there a healthy accelerator pump shot when you work the throttle? Is PCV valve function what it should be? If you have ignition points, is the gap correct? Are contacts pitted? Does your Mustang have the correct ignition coil? Have you examined the distributor cap and rotor for cracks and proper continuity? Do your ignition wires pass the resistance test? Is your fuel pump long in the tooth and not delivering adequate pressure and volume? What about the fuel filter? Even if it seems irrelevant, check it.
Though the nimble Ford six presents its share of tuning and performance challenges, it doesn't have to be a poor performer. If you believe in this engine, there's plenty you can do to get its performance back on the beam. Your greatest friend in engine tuning is the desire to troubleshoot. There are no freak occurrences nor is there magic, just physical facts. If you cover the bases step by step and pay close attention to detail, you can super-tune your Mustang six and wind up with a reliable powerplant that will give you a lot of driving pleasure for years to come.
Help For Classic Carburetors
Last year, our hobby suffered the unfortunate loss of Jon Enyeart and, as a result, his Pony Carburetors. We are gradually becoming familiar with other classic carburetor rebuilders in the industry. In Pittsburg, California, Recarbco performs concours restorations on vintage carburetors of all types--Autolite, Motorcraft, Rochester, Holley, Carter, Stromberg, Edelbrock, Zenith, and a host of others. Kurt Praxl has opened his own carburetor restoration shop in Western New York as KP Carbs/Carbontooters. Kurt was trained and mentored by the late Jon Enyeart when Pony Carburetors was located in Western New York. Kurt's work is outstanding and on a par with what you would expect from Pony Carburetors.
10 Choke function should...
10 Choke function should be checked. When cold, the choke should be closed, but not tightly. When the engine starts, it should be partially open and demonstrate a steady pull-off with engine heat. Fast idle should come off with a light stab of the accelerator.
11 Look for the obvious....
11 Look for the obvious. Never use sealer on a carburetor base gasket or spacer. Always use appropriate gaskets making sure they're in good repair. Heater hoses provide hot coolant for good cold start performance.
12 Once Terry Simpson discovered...
12 Once Terry Simpson discovered the incorrect 1100 carburetor on a six-cylinder Mustang at the Restomod Shop, he decided to check ignition timing and found too much. Someone installed the wrong 1100 carburetor and never bothered to check ignition timing, which begs the question--didn't they notice how poorly this thing ran?
We keep beating the PerTronix Ignitor drum, but the darned thing works so well it's a no brainer if you drive your Mustang. PerTronix introduced the Ignitor more than two decades ago and changed the world for those of us who grew tired of fooling with ignition points. The Ignitor is super compact and hides inside your Load-O-Matic or Dual-Advance distributor. And if you bury the Ignitor's wires in heat shrink, this thing defies detection.
Once installed and properly gapped, the Ignitor never requires service or adjustment. Count on replacing your distributor cap and rotor when you change spark plugs while giving the Ignitor a quick once over. Your Load-O-Matic gets a #1266 Ignitor or #91266 Ignitor II. If you have a Dual Advance distributor, order the #1261 Ignitor or #91261 Ignitor II. If you decide to stay with ignition points, don't do it on the cheap. Opt for a Motorcraft or NAPA tune-up kit with heavy-duty points with phenolic rubbing block and vented contacts. Go with a cap and rotor with brass terminals.
Is Spark Knock Harmful?
Ignition timing is not only important to power and fuel economy, but also engine health. If you're running too much timing (advanced), your engine is at risk for spark knock or detonation--that rattling sound you hear under hard acceleration. Light pinging isn't always harmful, but any pinging is unacceptable.
Spark knock typically occurs when fuel ignites prematurely on the compression/ignition stroke. It can be caused by a red-hot piece of carbon or early ignition timing. It can also be caused by combustion chamber dynamics, such as the 351C-2V with its open chambers and poor quench, or a lean air/fuel mixture. You want the optimum balance of good timing coupled with air/fuel mixture in order to keep combustion temperatures conservative. Detonation can be considered a more violent form of spark knock with opposing flash points in the chamber coupled with an ugly head-on collision mid-chamber. Spark knock and detonation act violently on the piston dome, wrist pin, and rod journal.
13 Look for hidden elements...
13 Look for hidden elements like bad grounds, poor connections, and chaffed wiring. Sometimes distributors are rebuilt and never get their ground wire back, especially with mass rebuilders.
14 Secondary ignition wiring...
14 Secondary ignition wiring has its own share of gremlins. Start your engine and observe in total darkness. Do you see arcing among the ignition wires? Crossfire and arcing to ground robs your six of a healthy spark.
15 Good connections are everything...
15 Good connections are everything to performance. Ignition wire connections must be confirmed at each end and installed using a dielectric compound. And remember, ignition wires don’t last forever. Replace them every four years regardless of how often you drive your Mustang.
16 Distributor caps offer...
16 Distributor caps offer their own share of gremlins, including hairline cracks that you can't see. However, high-energy electricity finds them with ease. When in doubt, swap caps and see if that makes a difference. Choose a cap with brass terminals.
17 Timing marks are located...
17 Timing marks are located on the timing cover and are marked accordingly. At idle, you want 6-12 degrees BTDC according to Ford. Total timing should be 34-36 degrees BTDC at 2500 rpm. Road test and listen for spark knock under hard acceleration.
18 Checking valve lash should...
18 Checking valve lash should be an integral part of engine tuning yet few do it. Although 170/200ci Mustang sixes had hydraulic lifters, cam lobes and lifters wear down and proper valve lash winds up lost in the process. We’ve seen some Ford sixes with hydraulic lifters equipped with adjustable rocker arms. Most were non-adjustable, which calls for different length pushrods to take up clearances.
19 If you want your tuning...
19 If you want your tuning spot on, perform both a compression check and a cylinder leak-down test. With the data, you can ascertain engine health. A compression check alone isn’t enough confirmation because it is only static compression. Leak-down is more dynamic compression and real evidence.
20 Another barometer of engine...
20 Another barometer of engine health is blow-by. If you have oil around the filler cap, it's an indication of excessive blow-by from poor cylinder sealing. It can also be a dysfunctional PCV valve or plugged draft tube.
21 While you're checking...
21 While you're checking engine health, check intake manifold vacuum. At 500-575 rpm idle speed, you should see 17 inches of vacuum. A bouncing needle or low vacuum indicates a wiped cam, valve leakage, low compression on one or more bores, or intake manifold vacuum leak.
22 Some performance issues speak for themselves, like this fuel filter and rubber hoses, which are a fire hazard when positioned over a hot exhaust manifold. What's more, you are at risk for vapor lock and no start while hot. Fuel lines should be hard lined between the pump and carburetor where possible, with the fuel filter located away from a hot manifold.