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Gun Doc,
There are a few things you should address given the engine/carb specs off your last post. Some things free and easy some thing can be more expensive. So let's start with the free and easy.
1) Float level and fuel pressure properly adjusted.
2) Carbs synchronized.
3) Timing - Try 14-16 degrees initial timing with about 20-22 degrees advance for a total of 34-38 degrees all in by 2500rpm.
4) Idle mixture adjustment - Try getting your idle speed down around 650rpm when adjusting the mixture screws. You want to make sure the throttle plates are closed as much as there allowed. With engine off lightly, carefully turn the mixture screws(clockwise) all the way in ( I remove the idle mix screw springs for this so I have a good feel). Once you have determined the fully seated position index the screw(12 o'clock) for future reference using a yellow paint marker or something that will last while. You now have a nice quick visual for where your idle mix screws are set. Reinstall the idle mixture screw springs and set all 8 mixture screws at 1/2 or 3/4 turn out. You now can turn each screw one cylinder at a time in/out (lean/rich drop) to achieve best idle. Too lean you will have a slight pop out the side pipe. If so tweak it a little rich until no popping is heard. End result should be idle screws between 1/2 and 1 turn out each. If over one turn you can try going smaller on your idle jet then tune with your idle jet holder. You should move down to a 55-60 idle jet from your 70 idle jet. As for idle jet holder try 90 through 120. (to save money on idle jet holders I have purchased the smaller size and precisely drilled out larger until I am where I need to be. Also you can solder the orfices shut then precisely redrill to the I.D. you want to try. Just make sure you cleanup any access solder on the inside bore of the idle jet holder without removing any original brass. Once you get to your final and proper jetting size purchase that particular size). Once you get your idle mixture and idle speed circuit tuned you can increase your idle speed to where ever you feel comfortable.
5) Your F7 emulsion tube is rich. You should achieve better midrange (pickups, 2000rpm to 3000rpm range) by going to a leaner (larger diameter) F16, F15 emulsion tube. Above this rpm you will be tuning your main circuit with your main jets and air correctors, although you can affect your midrange driveability by tuning with the main jets some. Remember this, changing a main jet richer or leaner will affect the main circuit fuel mixture throughout the entire rpm range. Changing the air corrector jet will affect the main circuit fuel mixture in the upper rpm ranges.
What I have done to reduce the midrange stumble is to lean out the midrange by installing the leaner emulsion tubes then leaning out my main jet until the stumble disappears. Then do some full throttle passes (hold in the clutch and cut the igniton) and check you spark plug colors. Tune the high end by changing the air corrector jets richer/leaner until your mixture is just right.
Remember, if you change one area of your jetting you will most likely have to tweak another.
Goodluck.
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