Hello Harigo
This is my experience with side and rear induction engines. I've used both the 3W 75I and the 3W 75us. The side carb (3W75us) had quite a bit of tuning issues due to the varying air pressure in the cowl. It was quite a hassle to get it to run, in all attitudes, to suit me. On the other hand the 75i had it's carb partially inside the fuse and proved to be a superior performing engine, due mostly to the constant air pressue in the fuse, only requiring a small needle adjustments. The rear carb engines are a little more trouble to mount, cutting hole in firewall and standoffs. The standoffs, I cut from 1" dowl. A rear induction engine will be my choice everytime where availabile.
Ralph