The O.S. .75 AX weighs in at a none-to-svelt 26.46 ounces. I'd recommend the outstanding Thunder Tiger F-91s 4-stroke, which weighs in at 25.7 ounces. It's very easy to set up and tune, very reliable, and a stump-puller of a 4-stroke that will only get stronger and stronger over the years as you continue to fly it.

Ironically, it's actually a less expensive engine than your current O.S. .75 AX. It's available for $194.99 with free shipping:

http://www.thundertiger4u.com/thunde...s-p-13121.html

The folks at Radical RC have it listed for $184.00 plus $3 USPS shipping:

http://www.radicalrc.com/shop/?shop=1&cat=6

And last but not least, Infinite Hobbies shows the F-91s at $184.99 w/ free shipping:

http://www.infinitehobbies.com/morei...p?part=TTR9801

This is a great engine at a great price. It will also come within .75 of an ounce of balancing your plane exactly like your .75 AX does. If you are wearing your O.S. Max/Saito blinders, hower, my apologies for wasting your time.