I've got two 25 size planes flying right now. Looking from the front, one engine is mounted with the cylinder at about 7:30. The other engine cylinder points straight down. Both idle with no problem. In fact, the one straight down first had a Saito .45, then an OS 25FSR, and now an OS 32FSR. All idled great once set.

One trick is to spend time adjusting the engine while the cowl is off. Start it up and taxi it around for a while. Once the idle works reliably while taxiing, iIf the flying characteristics will be ok, go ahead and fly without the cowl. This will make it much easier to adjust the low speed needle. Note, since most low speed settings require the use of a screw driver very close to the prop, you should always shut the engine off before changing this setting.

Hope this helps.