I'll add my 2 cents worth also (I have 3 Saitos and 2 OS 4 strokes).

The ASP is the same engine as a Magnum. They are made in the same factory, just different names put on them. Both engines are clones of the OS.

Break the engine in slowly. USE A TACH !!! In order to set up a 4 stroke you will need a tach. The first couple of runs keep the rpms to 6,000, then gradually increase the rpms over the next few tanks. While breaking the engine in, run the engine for about 5 - 6 minutes while varying the throttle then let it cool for about 15 minutes, then repeat.

Your MAX rpms are going to be ABOUT 10,500 (depending on the prop and nitro content).

Once the engine is broken in (typically about 5 - 6 tanks of fuel), adjust the engine to max rpms, then back off about 300 rpms. Once the high end is set, do the low end (I usually adjust my low end to about 1,800 - 1,900 rpms. The low end rpms will vary by engine).

After you adjust the low end you will most likely need to readjust the high end.

IF THE ENGINE IS NOT PRODUCING SOME SMOKE AT FULL THROTTLE IT IS TOO LEAN - RICHEN IT UP A LITTLE.

I highly recommend adding some castor oil to the fuel (about 3 oz per gallon). While the castor is a little messy, it will protect your engine from a "lean run". I have well over 5 gallons through my Saito 72 and the only thing I have had to do is adjust the valves after about 4 gallons.

I also highly recommend using an OS "F" type glow plug - I have had no problems at all using the OS "F" plugs.

I use 10% nitro fuel and have plenty of power.

Before flying, I use the "Nose Up" method to make sure the engine is running properly. Put the engine at full throttle, then pick the plane up and point it straight up and hold it that way for about 8 - 10 seconds. The engine rpms should stay they same. If the rpms speed up or slow down the high end is not adjusted properly. If you fly like that you have a high probability of a flame out.

As for the plane: RE-ENFORCE THE FIREWALL I have seen the firewalls come off just by a slight bump and I saw a U-CAN-DO firewall come off in mid air with a Saito 72. I also suggest re-enforcing the fuselage by the wing. It is a weak point an can break on a rough landing.

Personally, I feel the 91 is overpowering the plane. I have seen several U-CAN-Do's with almost unlimited vertical running OS 70's and Saito 72's.

Good luck with the plane and engine.