I'll admit that I have an advantage over the average joe when it comes to fuel mixture. I've been tuning dirt bike carbs for a while now, and I have developed that special "feel" for when my mixture is off. This Holley carb is WAY simpler than a Keihin FCR on a more modern 450f/250f. For example, the FCR has a pilot jet and mixture screw (idle and barely off idle circuit), jet needle profile and height (mid range circuit), and main jet (top end circuit).
I can give some pointers in detecting the quality of your fuel ratio by "feel". First, the better way to do it is with an O2 sensor and rich/lean meter or multimeter/voltmeter. The next best way to do it is with a plug test. Install new plugs, get up to "haul ***" speed (about 2500 RPM I'd guess) for a short while (1 minute is probably fine), push in clutch and kill motor, stop vehicle in neutral or with clutch in, check plugs, light tan is good, white is too lean, brown is too rich, black is TOO rich. I have no $$ for sensors and bung welding into the exhaust, and I have no long flat "haul ***" stretches where I can get to and perform this test.
Keep in mind this is all about main jet tuning
Pointer 1: Smell. Its easy to smell when a motor is running rich. With the top off, I can smell a small amount of exhaust fumes in the cab, and, if they are rich (smells like fuel), the main jets are too rich. If you don't smell fuel, the jets are either good or too lean. Make sure you don't confuse the rich smell with any fuel leaks you may have in the motor compartment. Non charcoal canister jeeps tend to smell like fuel all the time, so when you smell exhaust smell, pick it apart and determine if there is also a added fuel smell to it. Also, make sure you are only using the smell test at RPMs and loads that don't involve the powervalve, accel pump, or idle screws as these will all mislead you. So basically run this test at part throttle cruise (PTC) in the 2000 and up RPM range.
Pointer 2: Sound (assuming no catalytic converters). A backfire (while driving) usually means you are too lean, as do fluctuations in engine RPM for a steady throttle position. Alternatively, if you have an exhaust system you can hear off idle, you should also be able to hear it on decel and PTC. A quiet or silent exhaust pipe durning PTC or decel usually means too rich.
Pointer 3: Sight. This one is easy, black smoke is a sure sign of way too rich. Be sure that its not your power valve or accel pump making the extra rich smoke, those are separate issues. You want to make sure its not smoking during PTC or decel where there is no influence from other systems.
Pointer 4: Fuel mileage. Unless your power valve is always open (bad), or you are perpetually climbing a hill, or perpetually start-stop-start-stopping, your main jetting and timing curve make the largest impact on fuel economy. Without going into the timing curve yet, the main jetting is rich if you have poor economy. For example, I've been getting 8 MPG before attempting to make changes to the timing curve and main jets.
Pointer 5: Feel. If you have sluggish and smooth performance in RPM ranges from 1300 and up, your motor is likely rich. If you have poor and erratic and noisy performance in the same RPM range, your motor is likely lean.
Pointer 6: Temperature. A hot motor may indicate a lean setting.
The most difficult piece of information to obtain, and the piece I cant give you, is exactly what a great performing motor is like in all these categories. You have to tweak and tune up to and slightly beyond your best tune, to discover exactly where that mark lies.
I'm looking for a Scout II Dana 300. Drop me a line if you have any leads. Thanks