I tend to reduce development time for B/W films. First I adjust for temperature (my CPE has a minimum temperature of 21C), then I reduce for constant agitation, normally about 15%. This gets me my basic time, which I vary if I know the film contains predominately low or high contrast subjects. By the way, be careful if you use Ilford films. Some Ilford datasheets, have tables for both constant agitation and hand processing - use the right one !
For colour, I have my own process time - but that is because Im using a non-standard dev. I used the stated time during my brief experience with commercial devs and everything was fine.
My CPE2 has two speed settings. In my ignorance, I have always used the slowest speed but have since read that Jobo recommend the higher speed. As I never had a problem with uneven development, I havent made any changes to my regime.
I have collected several drums over the years and have found that some have worn lids. If you check the outside of the inner rim of the lid you will find several ribs in the plastic. These can wear flat. During processing, the developer does slosh against this seal, so some could be lost. For me, it was more a problem with fixing as the process causes more gassing and the increased pressure made the lid leak. However, if it is really bad I guess a leak could be causing your developer level to drop. New lids are available as a separate part from Nova Darkroom (
http://www.novadarkroom.com/)
The lids have a habit of popping off during the stop cycle (if you use a stop bath, as I do) due to the gassing caused by the reaction of the acid stop and the alkaline developer. Just be ready for it !
Levelling is important, as is using the drum support cradle. My CPE came without a cradle. If yours is missing, you can make one out of two bits of U shaped guttering, pop-riveted together -> )(
The only problem I have had is with incomplete fixing, and then only with certain Kodak films (Portra 400). Most of my experience is with Fuji films which always seem to fix quickly and completely. I tend to push my fix to the limit of its capacity, so if I suspect that fixing is not complete I will pop the lid to make sure before starting the washing cycle. This will cause no harm to the film. Under fixing is obvious as a (sometimes opaque) veiling on the film. Apparently, over fixing can cause colour shift, but I have never had an obvious problem.
My CPE sometimes doesnt do the two turn trick. Mine is an old one that has an external "interrupter" that catches a peg on a four pronged arm. Sometimes the plastic ring that holds the peg gets gummed up. A good clean with dilute bubble-bath will get it moving again. I believe that the later "plus" models, and all the pro models, have an internal mechanism that is more reliable, but are a bugger to fix.
I do not have a lift on my CPE, but have never found this to be a problem. My normal process procedure is to -
Get everything - including the drum with the film in it - up to temperature (this takes ages). I use the temperature of the developer as a reference, as everything else is much less critical. You may find that the temperature at the top of the measuring cylinder may be slightly less than at the bottom, in which case a little gentle stirring is required. I take the temperature in the top third of the cylinder. I dont pre-soak.
- Start the processor turning
Pour in your dev as quickly as possible. Press on the lid and flip the drum onto the magnet. It should pick up and latch on easily. Start the timer.
Ten seconds from the end of time, pour the dev away (I use it as a one shot) and pour in the stop. Put the lid on, give the drum a couple of turns end-over-end, pop the lid off to let out any gas, then put the drum on the rotary processor again for a minute.
Repeat the above for the fix, but using what ever time the fix manufacturer recommends.
Wash in warm water, stabilise and hang up to dry.
If the film edge reference numbers are similar in density to one you had commercially developed, your processing cant be far out.
By the way, as you may already know, you can get two 120 roll films on a single spool. If yours has the red catch on it (not all spools do), you can load one film, press in the red catch, then load the second. If you dont have the catch, you will need to find another way of stopping the films overlapping - as they will due to the rotary action of the processor. Apparently, putting a kink in the trailing edge of the first film will work, but I havent tried this. Two 120 films processed for the cost of only 240ml of chemistry - cant be bad !