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How many hours of "rich" flight does it take to get fouled plugs

We have all seen pics like this (this one is for car plugs)

but I wonder if they really tell you much. I have found that if I lean aggressively during the pre-service engine run (necessary to mix up the oil and get it warm so it drains) then the plugs are clean. If I forget to lean (which I did once) they are full of oil and other crap.

IMHO the plug condition is based on the last few minutes, at most. Except for the lead deposits at the base of the insulator, which take time to build up.

Administrator
Shoreham EGKA, United Kingdom

Yes, this is what is confusing me. Our club PA-28’s are always run full rich thought typically trundle around at circuit height and the cross country flights that they do tend to be at 2,000ft. Hence at this height don’t need leaning.

I have done 300 hours in my PA 28 and have “got away” with this for 3 years. I do lean but I never used to on the ground. In that time I’ve seen the plugs at every Annual and every 50 hour check and they have always been perfect.

I’m starting to think that “the last few minutes of running” proposition seems to fit in with my experience quite well. I’m amazed I’ve not had issues before!

Thanks to all for the feedback.

United Kingdom

Hence at this height (2000’) don’t need leaning.

Yes they should. Full rich should only be used for full power.

LFPT, LFPN

I’ve never had a fouled plug with my O-320, but long ago I got into the habit of pulling the mixture almost to cut-off while taxiing, and also leaning most of the time while in flight (the only time I don’t touch the red knob while flying is when towing gliders).

I learned my basic PPL off a freelance instructor who had thousands of hours in light piston singles, and usage of the mixture control was taught right off the bat.

Someone I know here who recently got his first plane confessed to me it was the first time he had pulled the red knob back in flight! So another data point about proper leaning not getting taught properly.

Last Edited by alioth at 14 Jul 09:28
Andreas IOM

Interesting how different these experiences are. I’ve flown at least 1000 hrs in my -161 (O-320) and never considered plug fouling any kind of issue. I don’t lean for taxi or flight below 3000’ unless I’m bored or something, especially as there’s always a risk of forgetting to go full rich on descent and not noticing until go-around!. Except:

At the end of life of my first engine (2350 hrs) plug fouling at departure taxi became a big issue. Each run-up would need full power and heavy leaning to clear. The engineers said “the’re all like that”. Well no they are not, and this hadn’t been like that until now. It was always the front RH bottom plug. It was like this for about 50 Hrs until finally on an offshore Island at a deserted airfield I could not get full power. Eventually, after much leaning burn out, I departed over the sea and that was the last flight of that engine.

On inspection the front lobe on the cam shaft had a worn appearance unlike the rest. It was theorised that the valves were not opening correctly and drawing oil into the cylinder. But even at the end, this was still the best performing and best starting engine I’ve flown in the -161. So I’d suggest that persistent plug fouling is not normal in the Warrior and might be an indicator of trouble.

EGBW / KPRC, United Kingdom

When I did my PPL, leaning wasn’t encouraged below 3,000 ft. (I’ve just corrected this post). Generally leaning was something only to be thought about at or above 5,000 feet.

Also my first AMO actually used to rebuild engines (and had rebuilt my engine) He said something like “he’d seen a lot of wrecked engines due to incorrect leaning techniques and owners might be trying to save a few pounds on fuel but it was a costly error”.

The two experiences above meant I have only recently started properly leaning after fitting an EDM engine monitor. I only started to lean on the ground 2 months ago.

As Aveling says – it is interesting how different all these experiences are!

Last Edited by Archer-181 at 14 Jul 12:25
United Kingdom

I recommend using this thread for bizzare PPL training experiences

Administrator
Shoreham EGKA, United Kingdom

I can’t believe that the myth of “not leaning in the circuit” is still around! And then pilots complain that fuel is expensive … If I did that with my SR22 I’d have a fuel comsumption of 30 gal/h … (while I flew it with around 13-14 at lower altudes)

Last Edited by at 14 Jul 13:03

I would probably check the fuel system (carburetor or injection). If my understanding is correct, mixture is adjusted on every engine for full power. The reason being that you do not want, under any circumstances, be too lean while you are requesting full available power from your engine. If you are fouling your plugs while on the ground, at a lesser power setting than full power, I would suspect that your engine is too rich, that there is a defect in the cylinders where the plugs are fouling. I would be interested in more details: is it happening on all cylinders? Are both spark plugs affected in the cylinders that exhibit that behavior? If you are too rich, it could also mean that you do not benefit from all the power available during climb, the question would then be how much are you missing?
Engines are prone to see their settings vary with time. That is why I get my fuel system checked at least anualy and sooner if I see something unusual. Unusual could be a change in fuel flows generally observed, regular spark plugs fouling, unusual oil consumption, or any other change in normal behavior.
If you have a fuel injected Continental engine, manufacturers instructions are to check the fuel system settings every 100 hours or at annual, whichever comes first. I know a lot, alas, of owners that have been convinced by their maintenance provider that this is not important. I beg to differ…

I lean on the ground, not only to keep the spark plugs clean, but also because I want to have full power during climb, especially on hot days. It is always a trade off with cylinder temperature but I prefer to go higher on temps when I’m close to the ground and then use a shallower angle of climb to cool the cylinders when I am at a safe altitude. Flying in the mountains has convinced me that it was, for me, the safer bet. taking off for LFMR on runway 27 (slight upward slope) with no breeze in August is not a healthy sport if you are missing power. Density altitude is your enemy! The field is at over 3700 ft P alt, so with a temperature of 30°C means a density altitude of 6000 ft.
I think we all agree that to reach best-power at 6000 ft you need to lean… Obviously, in this case I will stay on the rich side of the EGT Peak, maybe a little rich, but I will lean. I happened to witness accidents where the pilot crashed because he had not full power at his disposal. Not pretty.
But again, this is only my own personal opinion!

LFPN Toussus le Noble, France

Well, maybe it is really time that we get airplane engines to a standard which every current car engine has. Mixture control has gone from automobiles for decades. It is more than obvious that a huge part of the pilot population is being badly taught and therefore unable to operate the mixture properly, so the only way to change that for good is to get turn key engines like any normal car has these days.

Personally I am very unhappy with the fact that a lot of aeroengines are simply much more complex and full of hassles to operate. A lot of people have problems even starting the darn things, including me at the moment with my bog standard O360 which has become really difficult to start but where maintenance can’t find any fault with… it takes the joy out of flying if every time you have to fight to get the thing going like a 1950ties Trabant.

Frankly, I envy those who have Thielerts or as I understand also Rotaxes who really can sit inside the plane, turn the key and voila, followed by a single lever operation during the whole flight. Seeing that in over 35 years of car ownership I’ve never had a single time where my engine did not start of misbehaved other than for a flat battery, the whole aeroengine state of technology is nothing but a disgrace.

Being as the status of our engines is, there should be a movement to see to it that finally the mixture myths HAVE to be taken to the grave and buried deep. Instructors who still teach not to touch mixture levers should be grounded and their licenses put to the shredder, renters and PPL’s who don’t mix properly should equally be taken out of circulation. Not to mix is to abuse the engine and to cause expensive trouble to everyone flying that plane. Maybe this has to start at the examiner’s level who should put a very heavy hand on misuse of mixture, up to failing candiates who don’t know how to use it. That would maybe wake the FI’s up finally.

LSZH(work) LSZF (GA base), Switzerland
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