This is why a timing light is a good idea, even if you're astute at tuning by ear. Timing marks allow us to see how timing events are unfolding. Watch them as you goose the throttle, which determines vacuum advance adjustment. Note how MCE Engines has marked this balancer: TDC, then idle timing at 12 degrees BTDC, then maximum advance at 34-36 degrees BTDC. This gives you a tuning window as a guide.
With the vacuum advance reconnected, check total timing, which can be done two ways. Total timing is checked at 3,500 rpm with the vacuum advance connected. Ideally, push for the maximum number of degrees before BTDC without detonation (pinging or spark knock). In most circumstances, total advance should be 34-36 degrees BTDC.
The rate of advance is checked by goosing the throttle to wide open and watching the timing mark with a timing light. If spark advance comes on too quickly, the engine will tend to break up (misfire) and ping (spark knock), which means you need to slow the rate of advance. If the engine noses over and doesn't rev quickly, speed up the rate of advance.
When the vacuum advance is dialed in just right, the engine revs smoothly and crisply. On the road, power comes on quickly without hesitation or spark knock. At sustained highway speeds, the engine should maintain a smooth demeanor without misfire. If you feel a slight misfire at cruising speeds or hear pinging under hard acceleration, you have too much timing.
Another area to check is manifold vacuum. Healthy manifold vacuum is normally 15-22 inches at idle. Checking manifold vacuum is just as important as checking compression and cylinder leakdown. It determines an engine's state of health. Note that manifold vacuum gets tricky when the engine is fitted with an aggressive camshaft or too much carburetor.
Good Carburetion
Pony Carburetors was founded in 1988 to meet the restoration needs of vintage Ford enthusiasts. Jon Enyeart founded Pony Carburetors as a natural extension of his skills and now practices his craft for fellow enthusiasts, continually improving his process through the years. A big part of what Pony Carburetors is all about is impeccable restorations and tuning classic Mustangs to run better. John has a good, in-depth understanding of how carburetors work and how to improve performance.
This is the Autolite 1100 one-barrel carburetor for 170 and 200ci six-cylinder applications. Pony Carburetors is reproducing this carburetor so you can order a new Autolite 1100. | 
This is undoubtedly the most disliked Ford carburetor: the Autolite/Motorcraft 4300 emissions carburetor first used in 1967. But Pony Carburetors can take your 4300 or 4300D and make it better. If this looks a lot like a Rochester Quadrajet from GM, it's because Ford borrowed a lot of Quadrajet engineering ideas during development. The 4300D is a spreadbore version of the 4300. |
Pony Carburetors does Holleys too. This is the 4150 Holley for the '67-'68 390 High Performance. | 
This is one of the best four-barrel carburetors ever made: the Autolite 4100, first introduced in 1957 and produced until 1967 when Ford switched to the 4300 to improve emissions. Pony Carburetors can set you up with a 4100 that is designed and tuned to your engine's specifications. |
Pony Carburetors completely disassembles each core, plates all of the appropriate parts, does any machine work necessary, and builds these carburetors to better-than-Ford specifications. | 
Jon test runs each carburetor before shipping. Anything not up to standards is sent back for correction. |