Aerovee High RPM

[BERoberts]

The idle on my Aereovee is too high at 1400-1500 RPM. If I retard the throttle, the engine quits. I just completed a Onex with a standard Aerovee and Aeroinjector. The needle is a 2.0. I have completed the tuning procedure per the instructions and get 3100 static RPM at WOT with normal CHT and EGT. The engine runs smoothly at anything above 1500 RPM and leaning seems normal. Several of the posts discuss changing the needle to a 2.5 or 3.0. Would changing the needle allow a lower idle speed? Any comments would be appreciated.

Brad
Onex w/Aeerovee

[Bryan Cotton]

I'm a beginner at operating the Aerovee. I can get 800 RPM if I lean properly. Not sure how that will work when I pull the throttle to idle in flight. Too low and it quits.

[gammaxy]

The manual says

A needle should only be replaced after tuning efforts have shown the installed needle is too rich or too lean across the entire throttle range

I'm not sure you've shown this to be the case, yet. First, confirm that the engine is warmed up. I have to idle around 1200-1400rpm for a few minutes while warming up. Well before oil temperatures reach 100F it will idle smoothly around 800rpm. If there's nothing you can do with the mixture control to idle smoothly below 1000rpm, I suspect the needle is currently too lean at idle.

I'd remove the air filter and use a sharpie to mark the needle in its current position where it enters the orifice. Then adjust it richer (counter-clockwise) by a quarter to half turn and lock it while watching the sharpie marks to be certain the needle stays where you set it. It's almost guaranteed to move back lean while you lock it, just make sure the sharpie mark ends up where you want outside the orifice.

Side note: I spent a while trying to get a consistent smooth idle around 600rpm and was never successful, so I ultimately set the idle stop to yield closer to 800 rpm, but 1400 is definitely too high.

[sonex1374]

If I retard the throttle, the engine quits.....The engine runs smoothly at anything above 1500 RPM and leaning seems normal.

Brad,

There are several possibilities about why this might be occurring - new/tight engine; idle too rich; idle too lean. You can't do anything about the tight engine until you get 20-40 hrs on it and it loosens up. If the idle is rich or lean, you can experiment with leaning at idle to see if that helps or hurts the situation.

If you lean at idle and it gets better, then you might be overly-rich and flooding the engine at low rpm. In that case, you need to switch to a 2.5 needle and re-tune at WOT. Then you can experiment with the idle speed and leaning again.

If, however, you can't lean at all during idle before it quits, it's likely the 2.0 is fine for now, but the engine needs to loosen up some before you change anything. I really doubt you're too lean at idle, so play with all the other possibilities first.

Jeff

[NWade]

While I am normally a “go with the factory instructions” guy, if you haven’t tried Jeff’s method for AeroCarb/AeroInjector tuning I *highly* recommend it:
http://www.sonex604.com/carb_tuning.html

As others have said: If you can idle at 1500 RPM see if you can lean it a small amount. If the engine quits immediately, you’re too lean at idle. Most of the AeroCarb/AeroInjectors like to run rich at idle, requiring a fair amount of leaning with the mixture knob in order to idle smoothly (then going full rich as you prepare to throttle up).

—Noel

[Onex107]

The first thing I had to do was eliminate the play in the ball joint in the needle holder. You will make adjustments in the 1/4 turn increments and I had a 1/2 turn of play in the ball joint.
Second. I didn't think using the marker was accurate enough when setting the needle. I marked the bottom side of the needle with the edge of a file. Making a shiny fine line under the beginning of the taper where they tell you to start your setting procedure.
This is starting point "zero" when installing the needle and the number of turns and parts of turns from there to your final setting need to be recorded so you can remove, reinstall, or change needles in the future.
The needle holder set screw is a 3/8 X 16 thread so you get .030 movement per complete turn.
My #3 needle is set at 2 1/2 to 3 turns and I don't have to lean at idle.

[BERoberts]

Thanks, guys!! I will follow your suggestions and let you know how it goes.