I know, I'm being a pest. But when it comes to being a pest, I'm the best! 
I'm pretty sure I have keyster needles in my '76 F1. I read on another topic they are way too lean from idle to 1/4 throttle. Can I cure this with bigger pilot jets and raising the needles? Or will it go rich at some point? I'm trying to gather as much info as I can and buy what I need to buy before I really get started. Gonna buy a borescope tomorrow and have a look at the cylinders too. When I get it running again I have a leakdown tester to hook up to it as well. Thanks a ton in advance for your support!!
Also to note, I have a long, bell-end Jardine slip-on installed that is really quiet. Any recommendations will be greatly appreciated!
The Keyster needles are too large at their base, which causes the lean-ness issue. Although it tapers to the same length, the taper is therefore more progressive (i.e., "faster") as it reaches 3/4 throttle (which is the range you will most likely be using).
The difficulties begin where the idle jets falls off before the needle taper thins out enough to make the mixture more consistent. There's some things you can try and that will help a little, provided you have a stock airbox. If not, all bets are 'off', as they say...
If you have roundtop carbs:
1. Increase the float bowl depth: instead of 26mm float depth, go to 24mm. This may cause a tendency for the carbs to overflow when the bike is on its sidestand, so remember to turn off the gas when parked. My K2 has been set this way since 1973 (using all Keihin parts, though). It increase the richness between 2000-3000 RPM.
2. Step up the mainjet a 5-size. Also use Keihin Jets: the Keyster jets run quite lean, and their tapers and numbers do not match up to Keihin's values. For example, their #110 mainjet runs more like a #103 in Keihin at 26mm bowl depth, and #107 Keihin equivalent at 26mm depth. The non-Keihin jets have differing angles where the fuel meets the metering hole. and the hole size is not the same, either.
3. Adjust the idle air screws outward slightly. I'd suggest trying 1-1/8 turns out instead of 1 turn, for starters.
4. Retard the spark advance rate a little bit. This is most easily accomplished by cutting off 1/2 turn of one of the spark advancer's springs, bending the new end outward to reattach to the weight. This will let the intake vacuum raise slightly by reducing the spitback at low engine speeds, helping to increase the fuel loading at a given throttle setting. You can preliminarily test this part by just retarding the timing plate a few degrees to see how it works, but it will lose some full-advance angle this way in the end. Many city-only riders have found this works well when combined with lower-octane (regular) gas, leaving it retarded all the time for cleaner sparkplugs. Somewhere in between "T" and "F" at idle speeds is appropriate. I have also run my own 750 with stronger springs since 1976, with terrific results!
