fairly new engine that has good high rpm ( 3/4 turn on needle valve) but lags when going up from good idle or low rpm. what do you suggest? the manual recommends 1 1/4 turns for high speed valve but that turned out to be 3/4 turn. os says 3/4 is fine if it runs good.

Probably your low speed needle is set too rich.

Peak then richen 500 rpm on high speed needle, then lean out low till good response & good idle, then go back peak & richen high speed again & you should be set

Do a search on this forum about engine tuning. Whenever someone asks me how many needle valves turns out should their engine be set, I always reply, "whatever it takes".

You should be running 300-400 rpm shy of max lean rpm on the high end needlve valve and your low end needle valve should be set for reliable idle and snappy transition.

How long should you expect it to idle and still transition snappy?

10 seconds are good for me but more is often attainable.

When the idle is set correctly, an engine would theoretically idle all day long, without loading up.

When you come in for a landing, on a long, steep final, you could be idling as long as 30 seconds. If when opening up after a missed landing, the engine just "barfs" and dies, you've got trouble.

If the engine would not open up immediately after 30 seconds of idling, it is not adjusted properly.

Sincerely,

I've actually had engines idling for 5 minutes or more on the flight line, waiting for traffic to clear.

Here's how to set the low speed mixture:

1. Find the lowest reliable idle the engine will maintain.
2. Let it run for 10 seconds, then jam the throttle to full.
3. If the engine gurgles/sputters, and smokes a lot, shut down and turn the low speed needle clockwise 1/8 of a turn. Go back to step 1.
4. If the engine sags or completely stops, turn the low speed needle counterclockwise 1/8 of a turn. Go back to step 1.
5. If the engine transitions smoothly, re-tune the main needle valve, and go flying!

An major indication of the engine being too rich is that the RPMs drop when you remove the glow ignitor after starting.

Typically, the low speed mixture setting on OS .46FX engines is 1/2 to one full turn too rich.

Mkirsch,

You second what I wrote in another thread, and here, about OS engines coming mal-adjusted too rich. They are playing it safe, but many modelers I know are totally reluctant to even touch the idle needle. I can't see why.

Sincerely,

My 46 FX came 1/2 turn too rich on idle too.
I do not agree, though, that en engine should be able to run its tank empty and still be able to go full bore instantly. That is a slightly lean condition because in the air, and as the tank empties, you get leaner (too lean). It is perfectly normal, in my opinion, that an engine loads up a little bit if let at idle too long. All you have to do is put throttle slowly.

Has anyone tried a stall turn with a lean idle? IMO, I do lots more stall turns than waiting on the flight line.

A god starting that has worked for me is to close your low-end needle. Now open it 1 full turn. You should be pretty darn close.

Good advice all over the place here but I've had two of these OS 46 FXs and I've seen two more at my club ALL have the same problem. Part of the difficulty in getting the midrange right is the remote needle on this engine and it is very hard to get it to idle without loading up. Follow all the good advice here and run your 46 until it wears out then get a Thunder Tiger, older OS, Irvine or Tower Engine.

Good luck.

Ignacio

Nacho,

The only way the high speed needle can affect the midrange, is if it passes wind (air leak...).
The entire 0-75% throttle range, is up to the low speed needle's mixture curve. The tapered needle is pulled out of the spray-bar, as the throttle is advanced, so tailoring the mixture curve.

If your engine is too rich in the midrange, the needle may be worn, or wrong.
Sorry, I don't know where to find a replacement, or an aftermarket needle. Ask Bill Baxter.

Sincerely,

I agree with the issue on remote needles. Besides potenital leaks, you have "delayed" tuning issue. After any adjustment on the needle valve, it takes a while beofre the engine is effected. I think it is easy to starting tweaking too much, too fast

Put a Perry on it ! MAX H.