Hey all,
   Looking forward to becoming a part of this forum!

I just bought Randy Lewis' 1030. It is the featured plane on the minimax 1030 page:
https://www.teammini-max.com/online-store/aircraft-kits/1030f-max-103/


Beautiful plane, he did incredible work. It currently has a Rotax 377 dual carb in it. Im having trouble getting spark, chasing down the issue in the CID ignition. But according to his logs, the plane weighs 386 pounds..... Im thinking the 377 will be way too underpowered for this. Has anyone put a 503 in the 1030 airframe? I know that is not normal but he added extra bracing when building this plane so its pretty tough. The 503 is only like 15 pounds more than the 377.

Chase down the problem. The 377 works well on the 1030. I am inclined to suggest that you weight the aircraft first. 386 Lbs does not sound feasible. My 1600R with 447 is aroung 153 Kg -336 lbs. 386 would be with 30 litres of fuel, as well.

Thxs for the reply Tom! Yep will definitely weigh her and do a weight and balance test. But i have a weedhopper with the same engine and it only weighs 260 pounds. It has much more wing area and only climbs out at around 3-400fpm with me in it (220lb) and 5 gals of fuel. So Im worried the climb rate of a heavier bird will be much worse. Thats why I am thinking of the 503 as a backup engine.

Stroid, I'm currently running a points ignition 447 complete with an electric start and battery in my 91 (UK designation for a 1600R), even with a coarse pitch prop she climbs at 600fpm with me at 196lbs and full fuel. However, I'm going to fit a 503 as I have one lined up and I operate out of 200 yards.

Adding 15 lbs to the nose may also mean adding 5 lbs to the tail.  You may also want more fuel.