Aerocarb too rich at full fuel

[Bryan Cotton]

Interesting thing happened today. On climbout, 500', the engine showed some roughness. The line boy had given me 2 more gallons than I asked for so the aircraft was a bit overfull, but it was not leaking out of the vent. I thought it over for a moment and then leaned it out. Smoothed out nicely.

So it makes sense that higher fuel level will result in a richer mixture. Anybody else have similar experience? Should I do a full throttle runup and lean? It was ~15F out so very dense air.

I flew 2.3 hours today bringing my total to 35.

[flyingbear]

FWIW I have 250 plus hours on my Aerovee and I ALWAYS lean. From about two min after startup I lean for best rpm. At idle I get an increase of about 150 rpm and on takeoff I get about 200 rpm increase. My engine is much smoother when leaned. The transition to TOO lean happens very quickly so be careful. I fly 93oct no eth only and my oil stays very clean looking for many hours. I always take off with full fuel and rarely use more than 7 gallons before landing.

[Bryan Cotton]

FWIW I have 250 plus hours on my Aerovee and I ALWAYS lean. From about two min after startup I lean for best rpm. At idle I get an increase of about 150 rpm and on takeoff I get about 200 rpm increase. My engine is much smoother when leaned. The transition to TOO lean happens very quickly so be careful. I fly 93oct no eth only and my oil stays very clean looking for many hours. I always take off with full fuel and rarely use more than 7 gallons before landing.

So do you do a full throttle run-up with brakes locked to set your mixture for takeoff? I'm curious what technique you use. In the air is easy.

[GraemeSmith]

Interesting thing happened today. On climbout, 500', the engine showed some roughness. The line boy had given me 2 more gallons than I asked for so the aircraft was a bit overfull, but it was not leaking out of the vent. I thought it over for a moment and then leaned it out. Smoothed out nicely.

So it makes sense that higher fuel level will result in a richer mixture. Anybody else have similar experience? Should I do a full throttle runup and lean? It was ~15F out so very dense air.

I flew 2.3 hours today bringing my total to 35.

I do not think the extra fuel caused you to over rich. I've a lot of hours on mine and take offs at all sorts of different fuel levels - and I don't think that is a factor.

But I do find the Aerocarb is sensitive to:

- Density Altitude
- Abrupt throttle advances.

Having to lean at a high DA seems counter intuitive though. Really low Density Altitudes usually require a richer mixture.

I'm going to assume that by 500ft - you didn't suddenly slam the throttle forward a touch.

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Yes to lean for best mixture prior to take off - that's SOP where I live.

Yes to smooth throttle operation.

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Perhaps as things settle in you need to revisit the carb tune. Check the needle is still tight in the holder etc.

[Bryan Cotton]

Graeme,
I think you meant that having to lean at a low DA seems counter intuitive, and I would agree.

I pretty much never do anything but smooth and slow on the throttle knob. And your assumption is correct - at 500' the throttle was all the way in where it had been since the takeoff roll.

I noticed the slight bit of roughness and was climbing parallel to the runway, opposite the pattern. It seemed to be increasing in roughness, but slowly. I was debating my options, and high on the list was a return to the ground. The effect was immediate when I leaned a bit and that gave me the confidence to fly around the airport. When the Aerovee seemed happy after a minute I departed the pattern.

I've not seen this since, but we have not had those warm 15F temps here lately. So, we have been taking off full rich.

Some history on my Aerocarb, it ran great out of the box with the #2 needle and set up as per the manual. I crimped the threads a little per the manual, or maybe it was a service bulletin. I did have high EGTs however. So, I made it a 1/4 turn richer. I also added a ball bearing between the needle holder and the lock screw. Still ran great, EGTs still high. Next time around I went another 1/4 turn, and I have good control of my EGTs and am still able to shut down with the mixture (though I generally do this with the fuel shutoff). I did notice a change at idle. When pushing in the mixture to get the engine to light off, I'm a lot leaner on the mixture knob at start. It still runs great.