To Lean or Not to Lean?

Most all of my time has been in a J3 with no mixture control so I really haven't had to think about it. Now my 0-200 powered PA11 has a mixture control. I have basically flown it around for the last year and a half with the mixture full rich.

Mostly fly below 3,000' MSL

What are recommendations on leaning the mixture?

Larry.

It's going to depend on what carburator you have on each engine. The J3 probably has a Stromberg which doesn't benefit greatly from leaning whereas the PA11 with O200 most likely has a Marvel which responds very well to leaning. Both carbs have different mixture control types that work in totally different ways. Look up info on Stromberg carb mixture and how it works. The Stromberg carb is mostly self-adjusting for mixture but has a marginally useful mixture control that is used above 5000' MSL to improve performance. Below that altitude the mixture isn't very responsive.

Personally I'm going to fix up my Stromberg and try to set the mixture up and see how well it works. Some people have reported less plug fouling with it pulled all the way out lean to taxi. It can save you a bit of fuel in cruise under 5000ft but it's pretty marginal from all reports.

Long story short: probably not worth hooking up the mixture on that J3

Since the OP appears to be now operating an O-200 engine...

If you want to get anywhere near "book" performance with your O-200, you will need to learn to lean the engine. In cruise flight at around 3000' leaning to the point of roughness, then enriching back to "smooth" operation would reduce fuel flow by as much as 1.5 gph.

If you're not familiar with how to lean your engine, get some time with a CFI who can show you when and how to do it right. It's important to know (and practice) enriching the mixture before adding power at lower altitudes, and it's equally important to know NOT to operate full-rich at higher altitudes (typically above 3000' to 5000' density altitudes).

The O-200 I had in my Champion 7ECA also benefited greatly from leaning "brutally" while on the ground. Before my mechanic had me start doing that, I was dealing with fouled plugs constantly.

The technique for "brutal leaning" is to lean the mixture as much as possible – to the point the engine would stumble if you add throttle – immediately after engine startup, and keep the mixture as lean as possible during ground operations. When you begin your taxi, you will need to enrichen just enough to support taxi RPM. The whole point is to keep the mixture lean enough that lead buildup won't happen. The good news is that this "brutal leaning technique" at very low power settings (idle and just above idle) cannot hurt anything.

Once you are ready to do your pre-takeoff run-up checks, you go back to full rich for those checks. Once they are complete, if you'll be taking off immediately (uncontrolled field with minimal traffic), just leave it rich. But if you (like me) operate out of a busy towered airport, I would go back to the "brutally lean" mixture to keep those pesky plugs from fouling again. Just remember to go back to full rich before you take off.

But don't worry: the reason for leaning as far as possible while on the ground is to make sure there is no way to take off with the engine leaned. If you go to full throttle with it leaned "to the max" like I described, the engine will quit immediately. Embarrassing? Yes, but not fatal to your engine as could be the case if you went to full throttle with the engine leaned way more than it should be for takeoff...

Ah, yes I missed that with the confusion between the J3 and the PA11. Yes, with a Marvel carb on an O-200 normal leaning practices apply and can benefit operations greatly.

Just to play devil's advocate here a minute though, why not just run unleaded gas and do away with all the intense leaning routine so as to not lead foul the plugs? These little continentals run such low compression that 100LL is actually almost 3x the amount of lead of the fuel they were originally certified with which was 80LL. They run just fine on 90 octane unleaded and my C85 plugs don't show a bit of lead fouling or otherwise. Most small continentals have been run for ages with zero leaning and have made it far beyond TBO doing so.

Crash said:

....Just to play devil's advocate here a minute though, why not just run unleaded gas and do away with all the intense leaning routine so as to not lead foul the plugs?.....

Click to expand...

That.
Through the years, I've operated an O200, O300,O320, & now an O470 on 75% to 100% 87 octane unleaded car gas.
Lots cheaper, plus runs better & doesn't foul plugs.

I always found it interesting that Lycoming recommends NOT leaning most of their four cylinder engines below about 5000 feet. At Piston Engine Scool, I asked the question. Instructors response was a smile and the explanation that with altitude greater than that, those engines cannot make more than 70% of rated power. And, when operating at less than 70% power, you can’t damage those engines by leaning them. Some Continental engines “prohibit” leaning above around 70 % power as well.

MTV

Found this You Tube video from Mike Bush explaining leaning.
Leaning Basics - Bing video

Larry.

Crash said:

Ah, yes I missed that with the confusion between the J3 and the PA11. Yes, with a Marvel carb on an O-200 normal leaning practices apply and can benefit operations greatly.

Just to play devil's advocate here a minute though, why not just run unleaded gas and do away with all the intense leaning routine so as to not lead foul the plugs? These little continentals run such low compression that 100LL is actually almost 3x the amount of lead of the fuel they were originally certified with which was 80LL. They run just fine on 90 octane unleaded and my C85 plugs don't show a bit of lead fouling or otherwise. Most small continentals have been run for ages with zero leaning and have made it far beyond TBO doing so.

Click to expand...

I'm in 100% agreement with Crash on this point... I would have preferred to use non-ethanol MoGas if it were reasonably available around here... But none of the airports (within range) carried it (until the new Buccee's was built – well after I sold the Citabria). And even now, the cost of Buccee's 93-octane non-ethanol MoGas is higher than the 100LL sold at KSWI (Sherman, TX).

My airplane was a 1965 7ECA built by Champion, a couple of years before Bellanca purchased the type certificate and began building their own. The previous owner flew it off his back pasture, and used non-ethanol auto gas only, supplied from his personal "farm" tank supply. Unfortunately, that wasn't an option for me...

The plane actually came with the Petersen auto-fuel STC paperwork for the engine, although no 337 was ever filed with the FAA, nor is there a logbook entry to reflect the application of the STC. I asked my mechanic (IA) about it, and he said I would also need the EAA's airframe STC (cheap), but that he did not believe this specific airframe (7ECA) and engine (O-200) combination was covered in that STC. He could only find references to the later Bellanca and American Champion 7ECA powered by Lycoming 0-235s...

I could have followed up on that, but once I realized non-ethanol fuel wasn't available for purchase locally, it became a moot point.

Or as my daughter would say, "It became a moo point..." You know, like a cow, whose opinion on the subject just doesn't matter. It's "Moo." (Sorry - maybe too much coffee this morning!)

Lean the Continental O-200. I ran one for several thousand hours on 100LL in a PA-18 and after 800 hours of inadequate leaning started to stick valves. This gets your attention as it happened several times when taking off before I figured out what was going on. After pulling two jugs off seeing how much buildup was occurring always leaned that engine with the usual lead build up around the spark plug electrodes but no more stuck values.