Idle RPM's

[Aldo]

Hello Everyone,
I believe I have my AeroCarb reasonably well tuned. The Aerovee behaves well when moving from 1100 rpm to max power. I am, however, having problems keeping the engine running at full rich below 1000 rpm. As a solution, is it acceptable to set the idle stop so that the throttle stops in a position that maintains 1100 rpm? Will this be safe? Will it damage the AeroVee? I have read the manual to no avail for possible solutions. I have the previous owners 2.5 needle installed.

Thanks for your input,
Aldo

[gammaxy]

From my experience, I suspect that you are probably too rich even at WOT.

I flew a few times with my throttle stop set close to how you describe. 1100-1200 rpm increased my float down the runway probably by several hundred feet. I much prefer having the idle stop around 900 rpm where it is now (obviously that would mean getting the engine to run well at that setting). In my case I think I had an underlying problem with my fuel system that was making it hard to tune the aeroinjector. Once I solved that problem I've been able to idle nicely.

From what you are saying, I assume if you lean it out you are able to idle below 1000rpm? Are you sure you're not still too rich at WOT? Do you get any RPM rise moving from full rich towards lean at WOT? I get a noticeable rise of perhaps 30-50 rpm at WOT (don't know the exact number) and I get a little rise at idle when I pull the mixture full lean for shutdown. I think I am still too rich, but the engine doesn't feel like it will quit if I leave it at full rich at all power settings--I just lean for a little extra performance and fuel economy.

Are you satisfied that both ignitions are working? At WOT I can fly within a few mph on either or both, but it idles significantly better with both.

Also, are you waiting for the engine to warm up? (I assume you are since you have been testing at max power). Within a few minutes of startup I keep the throttle around 1000-1200+ rpm where it runs smoother than idle. Once I do my runup and have 200+ degree CHTs and 100+ degree oil temperatures I am able to idle around 900rpm nicely. This might take 5-10 minutes.

[Onex107]

I had the same problem with needles 2 and 21/2. A builder in Florida suggested #3. It didn't make sense to go to a richer needle, but I tried it and it worked. The #2 and #2 1/2 are too long. If you adjust the top end, the bottom end it too rich, and if you adjust the bottom end, the top end is too lean. Just for the heck of it, measure the length of the four needles. I found the 2 1/2 to be .040 longer than the others. And measure the play in the ball end of your needle holder. I found nearly 1/2 turn of slack there. I never could get the full rich rpm drop suggested in the book. Anyway, my #3 needle was perfect. My mixture is pulled out about one inch. I start and idle at 1000 smoothly. I take off and cruise at 3000 rpm and never touch the mixture from the original setting at start. The #3 taper is the right length to match the slide movement on my Aerovee.