RE: What engine for a H9 Cap 232 1.20(1/4 scale)
1.20 sized glow planes just do not, nor have they ever, done all that well once a gasser was tossed on the nose. Period!! Those that just want to go fast and hover all day will be pretty happy, I suppose, but if that's all you can do why not do it cheaper with a Something Extra or similar.
Just about every manufacturer out there advertises the weight of their engines with only the engine. It never includes the weight of the muffler, ignition module, ignition switch, ignition battery, etc. The only exception is a company like Zenoah that has a magneto instead of electronic ignition. If gassers were more powerful, then why the heck do we use a formula to size a gasser that comes out at 1.5 times the size of the suggested glow engine?
You want a good flying Cap? Then make it light and watch your c/g. You want a "Snappy Cappy"? Then make it hevy with a forward c/g. Either of the last two will doom most Caps in short order. Even if you just ahppen to be real good.
I'm a gas flyer all the way, but if the plane was mine I'd be dropping a Saito 1.80 on the nose and having fun. A gasser will just make for a lot of work for the installation, turn you into a Nervous Nellie for a few flights, then bring nothing but grief. Course, that nice, expensive gas engine you had up front will take most of the impact, and leave you with all the prestige of a gas engine owner with no airplane to fly.
BTW, a good intro to gassers starts at about the 50cc level. The stuff below that is pretty much a waste of time and money unless you fly things like Cubs and WWI biplanes.