Yesterday I mounted a 14x4 prop onto my Super Tigre .90. This is on my Sig Mayhem.

The engine ran considerably leaner than I've ever heard it run, and even though I gave it 1/2 turn on the screw, it actually flamed out in the air. I brought it back without drama. Tried again with a whole turn next time, and same result.

This has been the most reliable engine I've ever used, and I haven't touched the needle screw in a few years (it's been that good). I've never run anything less than a 6-pitch prop on this engine. At first I was baffled by why a diff pitch prop would throw the engine out of tune. But then in the middle of the night (when most revelations take place) it occured to me that it's because that flat prop isn't cooling the engine enough.

I was turning about 8,800 rpm with the previous 6-pitch prop, and it spun up to about 11,000 with the 4 unitil I gave it more juice at the needle. I think I'm gonna leave the 4 off.

Any thoughts?

I don't think airflow is the problem. The engine running at a higher rpm with a 4-inch prop can cause it to go lean. Still, you should be able to set the high-speed needle valve rich enough so that it runs well with this prop.

I think the 14x4 is too small for your engine, I had a lazy SC 91 that pulled a 15x4w and I know the OS 91 fx will handle a 16x4w no problem.
I think the super tigre should pull at least the 15x4 and probably a 16x4w, I bet that will fix your problem.

Jarle

ive never used a 4 pitch on my super tiger 90...always had a 13x6 on it...ran great

I tried a 14x4W on my .90 ST. It didn't die on my but was not enough of a load for it. It was trying to over speed the engine IMO. I have not tried the 15x4W yet but am planning to. This should be about right for it.

DAvid

I would also go with a 15x4w apc prop with that motor!I think,you will like it better.

Yup yup...the 14X4 is way too small for the engine! It's over revving and that is causing it to be a little unhappy. I use a APC 15X4W on my OMP Ultimate on a Super Tigre .90 motor and it's really happy. Heck I might give a 16X4 a go someday but the 15X4 has great spool up now and the motor is happy as is.

I run an APC 14x4W on my Magnum .91 2C Runs GREAT and turns about 11K on the ground (from memory [sm=confused.gif])

I have also run an APC 15x4W. Doesn't pull any better, spools up slower but larger prop wash, comes down to personal preference.


Maybe ST engines don't like small props [sm=confused.gif]

I think you will find the SuperTigre has a lot more power than the Magnum..