Anybody had hard starting due to Idle Mixture adjustment

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woxof

Pre-takeoff checklist
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woxof
Discussed in a thread recently....

https://www.pilotsofamerica.com/community/threads/idle-mixture-adjustment.109609/

....about how mechanics will typically adjust the aircraft's idle mixture for the home airport elevation. I believe that this could cause the engine to be excessively lean at a significantly lower elevation when the decide to fly there.

Has anybody from the higher elevations encountered this problem?
 
woxof said:
Discussed in a thread recently....

https://www.pilotsofamerica.com/community/threads/idle-mixture-adjustment.109609/

....about how mechanics will typically adjust the aircraft's idle mixture for the home airport elevation. I believe that this could cause the engine to be excessively lean at a significantly lower elevation when the decide to fly there.

Has anybody from the higher elevations encountered this problem?
Click to expand...

Nope. We learned that we should start our carb’d O-470 up here at 6000’ MSL with the mixture NOT full rich, and it would start EASIER, but it still starts either way.
 
@ -40 degrees and 30:10 Hg you must add fuel with the primer just to keep it running Long enough to get heat in the carb to keep it running.
 
Last edited:
Tom-D said:
@ -40 degrees and 30:10 HQ you must add fuel with the primer just to keep it running Long enough to get heat in the carb to keep it running.
Click to expand...
What does the bolded part mean?
 
woxof said:
Discussed in a thread recently....

https://www.pilotsofamerica.com/community/threads/idle-mixture-adjustment.109609/

....about how mechanics will typically adjust the aircraft's idle mixture for the home airport elevation. I believe that this could cause the engine to be excessively lean at a significantly lower elevation when the decide to fly there.

Has anybody from the higher elevations encountered this problem?
Click to expand...
No. I speak for everybody! Okay, I really don't speak for everybody. My fuel controller has some compensation for atmospheric pressure. The engine isn't started at idle anyway, about 1/2" of throttle is used. Anyway, talking to mechanics they really don't set them up any different in Denver than they do a sea level. We do have to lean at all times at higher elevations unless it's a turbo then full rich for full power.
 
Hard starting in carbed engines is very often due to clogged-up primer nozzles. There are tiny milled passageways in them that swirl the fuel and eject it, still spinning, out a tiny central hole. That causes the stream to break into a fine, fan-shaped spray, ideal for evaporating and mixing with the air for combustion. Those nozzles have fuel remaining in them after start, and it dries and bakes a residue in there every time you go flying, and sooner or later the nozzles either just squirt a solid stream, or they dribble, or they do nothing at all. New nozzles can work wonders for starting.

Delaying the start after priming sure doesn't help. The fuel ends up on the intake walls and dribbles down and out instead of being available for starting. Cold weather is much worse for this.

Another big factor is weak spark. Mags and plugs all wear and start losing their snap. That magneto can only do so much at cranking speeds, and if it ain't up to snuff you'll be fighting that engine trying to wake it up.
 
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