I am using the kf7 firewall forward with the 912, I have been told that you must mount batt or weight in tail to get cg correct. Any ideals on cg issues?
Rule number 47... never believe anything you hear about a particular model aircraft from someone who doesn't own one.
I have run several weight and balance sample loadings with a much heavier engine. Contact me off list if you would like copies.
With your lightweight 912 you should not encounter any CG problems. The CG envelope is very wide allowing you to mount your battery more for convenience than for CG. If you mount a battery back in the tail you may find you are unable to load the baggage to the maximum.
I mounted the battery in my Corvair powered model 7 behind the pilot seat. It helps with the CG of my heavier engine but it is mostly for ease of wiring and battery maintenance.