How important is it to have both engines running at the exact rpm. Assuming that the linkage is correct and fuel tanks have same length line to engine. Ive seen guys splatted with so much caster oil trying to get both engines running at the same RPM while others just tune to the ear. One pilot goes crazy when the engines run up at a deferent audible pitch. while others seem relaxed and let the engines settle in at a particular throttle setting. Do I need a RPM checker thingee or is the audible tone OK

Two engines running in synch is like listening to music, it should be pretty obvious when you reach the same rpm setting while you adjust the needle setting on one of them. Now, it never hurts to have an rpm checker, at least that gives something to validate the sound change they make when running in synch.

The whole world does not end if the engines are not in perfect sync,,,,,,,BUT remember that if they are not, you do not have equal thrust.
Yes, I try for the "Harmonic", at least at full throttle.
Now, warning. NEVER Tweak the low engine up to the faster engine or the weaker to the more powerful. It is inviting disaster as an engine out. If one engine is more powerful than the other, set the weak engine and back off two or three clicks rich. Now match the strong engine slightly richer to match the other.......NEVER THE OTHER WAY AROUND!!!
Now, always use a partner. Hold the plane vertical and go to full power. If one sags, NEVER TAKE OFF! The engines must be reliable in this configuration.
If you want to get fancy and really want the Harmonic sound at most throttle settings, put each engine on separate channel and mix together to the throttle control. Now, using exponential, similar to what the helicopter guys do, you can match the acceleration curve of the engines. It does take a little more careful setting of the needle valves for consistant equality, but it does work.
Good Luck,
Twinman

Why worry about sync of engines get on to www.glue-it.com and see how I did it with my Mossy.

wow what a flex job. I quess its not a twin engine but a twin prop You must have gottan the idea from a flex cable on a dremal. Have you flown it yet?

Just once it was a bit heavy on wing loading, The flex cable was the inner only not the outer flex drive From an electric drill from a DIY shop B&Q in the UK. I used a plastic tube as the outer. Not a new idea, but from the 60s a free flight model Mossy by F L Whittaker.