With either a hot or cold engine, you should not have slow cranking. That has nothing to do with the mixture. Futzing with the needles won't do anything to make it crank faster.
I would start with this known problem. First, make sure the battery is completely charged; put it on an external charger. Then do a load test. (Load tester from Harbor Fright, about $20.) Clean all the battery and starter connections, even if they look good. Make sure they are tight. If the battery tests OK, and you still have the problem, it's either the starter or your charging system.
The mechanical voltage regulators don't do a good job of keeping the battery charged, and the new Lucas ones are not correctly adjusted at the factory. You might just have a poorly charged battery.