Hey guys,

Was wondering if anyone could give me a guide to setting the high end needle on my Irvine .46
I've read quite a few and they all say about leaning the mixture to max RPM and then richening a few clicks. Is this correct? I try to follow this but then dont get a smooth transition from low to high throttle. Is there also some sort of distinctive sound that gives away whether it is too rich or lean?

Help would be appreciated. May also post any decent reply up on club wall as I know a lot of beginners have trouble with this.

Cheers!
Paul

there's also a low speed needle for a smooth transition from low to high. very minor adjustments on this one though.....just an eighth of a turn at a time. keep trying. on mine, i turn to rich on the high at full rpm's until it gurgles a bit then back to where it runs at max rpm's then again towrds rich 1/4 turn. i hope someone else jumps in here with some tips. this seems to be an issue with the new guys. i saw a guy lift his plane nose up at full throttle and the engine raced a little bit, then he put it down and dropped the throttle again. that plane ran really well. is this standard as well?

One should set the high speed needle first, lean it out until peak RPM is a cheived, then richen it up a 1/4 turn (that is turn the needle out a 1/4 from peak RPM). The check idle transition. If the engine stubles, it is rich and adjust the low speed needle (or screw) 1/8 turn in ward. Make this adjustment with the engine off (to save fingers, etc.). Start her up and test transition again. Have patience, you will eventualy reach the sweet spot and your engine will give you great performance.

Holding an airplane up tests to see if the rich setting is enough. If the engine quits, the high speed needle is set too lean. There is also the pinch test. Do a search on "pinch" and you will find a lot of information on that test.

Remember, slow process and have patience.

Cheers,

Chip

thanks chip.......it's nice to have new ideas explained to us . happy flying to you and happy easter

Paul,


What about the low-speed needle???

Oh, you didn't touch it? Most beginners tend to 'forget' it exists.


The low-speed needle controls and meters the mixture from idle to about 75-80% throttle.

It determined how the engine runs within most of the throttle's regime and even more important; how your engine will transition from one part-throttle setting to another and to full throttle...

Setting the high-speed only will only be effective at full throttle, so it is no wonder at all your engine doesn't respond at part-throttle. This since you have not bothered to adjust it there...


Please read the manual and search this forum about how to do the 'pinch test'. It is a popular method of finding a good starting setting for the low-speed needle.

Then adjust in very small increments, until the transition is just right.

You have to consider how much time is on the motor before reaching any type of steady carb adjustments. New engines constantly fluctuate on needle settings until they have been broken in.

Yeah, I guess I can't deny ignoring the low speed needle. It was set by someone very experienced at the club a few years ago when I first started with the engine, and has never been changed since.

Does this also need adjusting regularly then? I hate to sound stupid but I assume that all high speed needle adjustments should be carried out at full throttle...
Paul

Paul,


There is always the "safe" way, of ascertaining the current situation (whether it's rich or lean and by how much...) and stopping the engine to do the adjustment... This goes for both the high-speed needle and the low-speed needle.

But then you would eventually burn out your starter... and it will take you about one year...

------------

Someone once said there is absolutely no danger in flying. None at all.
It is crashing that is dangerous and you must never do it!...

The same goes for props and mixture adjustments.
You could put your fingers 0.05 mm away from a prop blade spinning at a Zillion RPM and you could never, ever hurt yourself...

But never put your fingers into the prop-arc, even at only 500 RPM... You would get hurt for sure.

It is much easier and faster, to reach the correct adjustment status by being very careful and doing it with the engine running. It is safer, however, to do it with the engine shut-down.

Hey guys,

Thanks for all the help, it really is good to have people like you to help all us beginners. Have been playing around loads with my engine and am haveing quite a bit of fun adjusting everything! Still slightly unsure about the high speed needle. I am leaning to maz RPM, and then just richening around 1/4 of a turn. I get a pretty smooth pickup near full throttle, but it seems to dip slightly a little before full throttle, almost likes its confused... sorry for the daft terminology,

Is this ok? Also, are there any distinct sounds that give away whether it's too rich or lean? What should the well tuned engined sound like?

Thanks

Paul

Any help would be appreciated guys! It's experts like you that help us beginners get through the first few years!

Paul

Paul,


Most engines, when the low-speed needle is set too rich, will spit fuel from the carburettor and emit more smoke and raw fuel from the exhaust, on throttle advance... During idling, the excess fuel will accumulate in the crankcase and will be fed into the cylinder when the throttle is advanced, resulting in too rich a mixture.
Some of the excess fuel will be spat out through the carburettor.

...But some engines don't know this rule, it seems... at least as for the fuel spitting.

In those engines, you must adjust in small increments leaner and see if the transition becomes better and smoother, or worse and more hesitant. If it gets better, it was too rich and vice-versa.

Each time, after making an adjustment, gradually open the throttle fully, to clean out the engine and allow it to idle for at least 20 seconds, before advancing the throttle rapidly (as fast as your throttle servo will) and checking the transition.

Too lean a mixture will result, in virtually all engines, in a hesitant transition, which the engine clearly 'stumbles' and chokes on the way up, it momentarily becomes less audible, due to a relative fuel starvation.

Adjusting that is done by gradually richening the low end.


Opening the throttle to check transition must always be done at 'servo-speed'. I.e. do not smack the throttle open in a millisecond. Even a perfectly adjusted engine is not immune to stumbling, if the throttle is opened too fast.