In 27 years of flying I've never run into an issue such as severe and perplexing as this and thought that I would see if any of you out there have any suggestions. I have a Saito 1.80 in a Great Planes Super Stearman and have been experiencing a multitude of issues with it. The engine was originally in a Sig Cap 231 EX and experienced a lot of the same issues many of which are contrary to the experiences with Saitos that I find from others (including the same engine in the same airframes). Just to answer a few questions ahead of time: all of the props are balanced, I use 15% nitro 2-stroke fuel and it has been broken in on a stand. Even though the engine is out of warranty it only has about 4 gallons of fuel through it due to the fact that it does significant damage to whatever it is mounted in and I took a few years off from the hobby.

Anyway here are issues:

1. Severe vibration to the point that it has broken bolts and most recently (this weekend in fact) it destoyed a Slimline pitts-style smoke muffler. It also fretted the exhaust port threads to the point where there are only about a 1/4 of them left which may make this whole thing a moot point. Hopefully they can helicoil it and I don't have to replace the cylinder.
2. Poor fuel draw (may be related to the above) but it also has the problem on the test stand. The needle valve has little impact on the top-end adjustment and rpm's top out around 9300 with a 16x8. Idle is very reliable and the engine transitions very cleanly.
3. The vibration really tunes up with props larger than 15" and it appears to reach a natural frequency with a 16x8 that if left running would dismantle an airframe in minutes. I've even changed props between the Saito and one of my OS 1.20s to see if it was the prop and the OS does fine. I've also tried Top-Flite, Master Airscrew, Zinger and APC props with the same effects.


Thanks in advance for the help!