Hello Sugarfoot,
There have been many suggestions here, all worth while!! I would like to suggest using 15% nitro fuel if you are not already. Also, if possible, move the engine forward to get rid of added ballast. The larger, foam tires on grass will be your BEST help. Buy them as big as you can without the plane looking "goofy"
I have been in this 2.5 years now with 4 ARF's and 3 kits built. ALL were tail heavy to one degree or the other. I have used about all the suggestions above to stop from adding lead. Most I have still needed lead.
When I built my kits, I got a rough idea of balance BEFORE final positioning and gluing of servo tray, battery, RX, and engine position. I did this while the plane was in the bones just before covering. I think (?), that at this point, there will be more weight at the tail after covering .....so.. I make sure it is slightly nose heavy at this trial period. I also balance lateraly at this time as the weight can be added to wing tips without cutting covering etc.
As far as the manufacturers "suggested engine size"..... I learned the hard way after my first plane to go to the largest suggested engine, OR one step above that.
I wanted trainer back in my hanger... so this winter I built an LT-25 with my old .40 LA planned for the power. I called Sig to ask if it would "PHYSICALLY fit" in the nose before I bought the kit. The tech guy said, "yes....... but it will be WAY overpowered!!" The .40 LA is a very reliable engine, but weak on power. This old .40
LA is great in this .25 sized trainer. I have probably flown it just as much as my other 3 Saito powered lo-wings this spring. I built it with almost a flat wing and have been "learning" more aerobatic basic moves with it. I feel if it goes in while learning..... I won't feel as bad as if it was my Satio 150 on my 4*120...good luck...
lownslo...