Today I fired up a New OS 46fx to run a tank of fuel thru it before its maiden flight next weekend.
This thing was VERY sluggish on throttle up, and never seemed to reach max RMP.

Am I doing something wrong?

Does OS not like 10% nitro? (all I have at the moment)

Does low end screw need to be leaned out a little?

I am begining to think I should have got another Tunder Tiger......
cause this isnt right from what I remember of OS in the past.

You have to break it in you know, right. If you have it set rich for break in, it should definetly have a slow throttle response. You should run about 2 tanks through before you put it in the air, so it is reliable. My .46fx is the smoothest idling, most reliable engine I have. The only deadstick's I've ever had was when it ran out of fuel, and 2 on the first 5 flights.

Definitely rich - both the high speed and the low speed needles, which isn't a bad thing when brand new.

When you have run a couple of tanks through, open the throttle fully, and slowly screw in the high speed needle. It should speed up, until you get to a point where it starts to die, then unscrew about 1/4 - 1/2 turn.

Then set the throttle to idle, and see if it's stable. If it is, open the throttle suddenly. If it splutters and finally picks up to max speed, producing a lot of smoke, the slow speed needle is too rich. If it dies immediately, it's too lean. Keep adjusting about 1/8th turn in this way until it picks up speed almost immediately.

OS engines are amazingly good at easily getting to satisfactory needles settings and sticking to them.

-David C.

So the 10% nitro makes no difference I guess?

Thats what I was thinking with any adjustments, but had to make sure.

Yes I know it has to be broken in thanks.

Its so rich it is collecting fuel in the muffler. At least that was my guess when I lifted the model to a nose up attitude and got a bath, and the pressure hose was disconnected when fueling, so it didnt get in there that way. I dont remember that happening before. will run another tank thru it this week.

You can also check the O.S. Max FAQ page:

http://www.osengines.com/faq/product-faq.html#q2

This is covered there.