I have a 46FX that is several years old with probably a 1000+ tanks of fuel thru the carb. Over the past year, I noticed that the engine will only run well if the needle valve is tuned out about 1/3 turn from stop. The last couple of times it was turned all the way in to run right. I replaced the needle valve and this made no difference. Fuel lines look good and engine seems fine. It has been a strong running engine, but this problem has me stumped. Running a pitts muffler.

Very likely, over time, the needle seat in the carburetor's been eroded to the point that it no longer meters fuel properly. This is indicated by the fact that it's passing fuel with the needle scewed in much farther than normal. This happens because, over time, the needle may have been closed too firmly a time or two, or vibration has caused the needle to hit the seat, or both. You would likely see a shiny area on the pointy part of the needle. This inidcates where the needle has hit the seat.

The only 'cure' is a new carburetor body. Here are the stock numbers and list prices of the parts you asked about:

OSMG3511 25681100 CARB BODY 40B 40-46FX $21.99

These parts can be ordered through any hobby retailer who sells O.S. Max engines and accessories.

This engine has the remote needle valve attatched to the rear cover. Could the same situation occur with this set-up? Looking at the old needle valve closely, there are small gouges and marks evident. The new needle valve made no difference, so in this case, it is probably just in the NV body?

Sorry, we got to thinking of the problem, and completely forgot it was the .45 FX. You are right. You'll need a new needle assembly.