Idle question
Posted: Sat Oct 25, 2014 10:04 am-----
SonexBuilders.net
A Forum for Sonex Aircraft Builders and Enthusiasts
https://sonexbuilders.net/
Idle question
Page 1 of 1
Posted: Sat Oct 25, 2014 10:04 amRe: Idle question
Posted: Sat Oct 25, 2014 10:31 amyou may be a bit rich for idle after the engine has warmed up. I taxi with a little mixture pulled out. Seems a lot of people have a rich idle mixture when the carb is properly set for full power.
Re: Idle question
Posted: Sat Oct 25, 2014 12:19 pm-----
Re: Idle question
Posted: Sat Oct 25, 2014 2:47 pmI don't feel completely qualified to comment since I am still tuning.
Do you get the 90-100 degree temperature increase between full rich and peak lean at WOT?
With the #2 needle I originally had a much larger increase and kept adjusting it until I got to around 120 or so. At that point it wouldn't idle very well and I had it quit while taxiing at low RPMs when the engine was warm. I took the aeroinjector off so I could inspect the taper on the needle and noticed that at idle there was no noticeable taper left. I had turned the needle so far to reduce the richness at WOT that there was almost no taper left for idle.
I switched to the #1 needle and now am pretty close at WOT but it seems very rich at idle. If I idle at full rich and then turn the fuel valve off to shut down, I get a 200+ rpm rise right before the engine stops. Hopefully someone will comment if they also see a similar rpm rise. Edit: Bill points out below that I am too rich. Sonex agreed and recommended I return to the #2 needle.
EDIT:
Since this post, I have removed my Floscan fuel flow meter and returned to the #2 needle. I flew it yesterday and other than being a little rich at idle and WOT it ran great. I plan on adjusting it a little leaner today. I don't know if removing the Floscan helped or if it was just the act of returning to the #2 needle installed in approximately the right position.
Do you get the 90-100 degree temperature increase between full rich and peak lean at WOT?
With the #2 needle I originally had a much larger increase and kept adjusting it until I got to around 120 or so. At that point it wouldn't idle very well and I had it quit while taxiing at low RPMs when the engine was warm. I took the aeroinjector off so I could inspect the taper on the needle and noticed that at idle there was no noticeable taper left. I had turned the needle so far to reduce the richness at WOT that there was almost no taper left for idle.
I switched to the #1 needle and now am pretty close at WOT but it seems very rich at idle. If I idle at full rich and then turn the fuel valve off to shut down, I get a 200+ rpm rise right before the engine stops. Hopefully someone will comment if they also see a similar rpm rise. Edit: Bill points out below that I am too rich. Sonex agreed and recommended I return to the #2 needle.
EDIT:
Since this post, I have removed my Floscan fuel flow meter and returned to the #2 needle. I flew it yesterday and other than being a little rich at idle and WOT it ran great. I plan on adjusting it a little leaner today. I don't know if removing the Floscan helped or if it was just the act of returning to the #2 needle installed in approximately the right position.
Re: Idle question
Posted: Sun Oct 26, 2014 4:50 pmThis may sound overly simplistic, but make sure your air filter is clean. I had a little bit of oil build up on my filter and developed a rough idle as you describe. I didn't think that little bit of oil/dust on my K&N filter would be a problem. An A&P (who also built an Aerovee) recommended trying it wouthout the filter and I was amazed at the difference. Changing the filter cleared it up.
Re: Idle question
Posted: Sun Oct 26, 2014 8:16 pmJust a quick suggestion. I find tuning to be trial and error as most. But, pull a plug, you can get a good idea how the mixture is by looking at the plugs. I'm sure you can download a plug assessment photo guide as well.
Re: Idle question
Posted: Wed Oct 29, 2014 3:24 pmIf at idle you pull the mixture out and rpms go up, like Chris Madsen, you are too rich. The #1 needle will be very rich at idle when good at climbout. The #2.5 needle will be on the lean side at idle when good at climbout. Sounds like Mike Beck is too lean at idle; what needle?
Bill
Bill