Tacpot,
If I relay my experiences with leaning my HAL26, I believe that it may help you.
In the cruise above 2500', I always leaned it.
I'd set the power to 2350 or somewhere around there, then very very slowly I would pull the mixture knob towards me until I could hear the revs rise. I'd then continue pulling it until the engine revs began to reduce.
Then I'd push the mixture towards the dash - and basically by judgement guesstimate halfway between increasing revs and decaying revs.
As you descend don't forget to enrichen it!
I have occasionally pulled the mixture out too far and the engine has begun to die, the prop is still whizzing raround ut it has gone seriously quiet up front...
but by pushing the mixture back, the little C90 always burst back into life. And after a moment of two, I would attempt to lean it with less vigour!
Stik