Art of leaning and carb heat

I fly a stock 150 without an EGT gauge. Recently, flying in the Alps I had what I think was an over-rich mixture. The situation was this:

Leaned at 9,500 feet by rpm gauge and ear, descended to 6000 feet or so with carb heat on, about 2100 rpm, enriched the mixture, rough-running engine, rpm surges, cured completely by selecting carb heat cold.

In retrospect I think I should:

a) Have descended about 2300rpm to reduce rapid engine cooling and reduce need for carb heat.
b) Gone much more cautiously and slowly with enriching mixture.

Does anyone have any comments on this? How do people deal with leaning and then use of carb heat which can result in a too-rich mixture?

If and when I go back to the Alps I shall probably fit an EGT gauge.

Anyway, any comments appreciated.

Thanks in advance,

David

What I do to lean without an EGT gauge is to lean until I can detect a little roughness and richen a little until the engine is running smothly. Then to make sure I am just on the rich side of peak, I pull the carb heat. If the engine slows down a little the mixture is set about right. If carb heat makes the engine speed up then the mixture is too lean and the mixture needs to be pushed in a little more. If you change altitude then you need to do it again. The best thing to do is to get an EGT. I have one airplane with and one without. ...Clyde

David
I have to do this all the time. I live at almost 7,000ft in the mountains. The ?ridge crossing? is at 9,500, I then have to descend to about 4,000 (in less then 10 miles) to the desert floor.

This is always a tough call. Back off the throttle and dive with the carb heat on and risk shock cooling or keep the rpm up and circle down while playing with the mixture.

What I?ve found works best for me is to back the throttle off to about 1500-1700 rpm, pull on the flaps, don?t use carb heat, descend to the new altitude, dump the flaps, throttle up and reset the mixture.

Temperature and humidity bear considerable on my decision to use carb heat, I?ve iced up my carb in the pattern at 2400 rpm in the winter, but I resist the urge to play with the mixture until I?m at the new altitude and cruise RPM. The reason for this (here come the replies) is because the mixture control is intended to be set between cruise and full rpm, at rpm?s less then that, you?re pretty much on the low speed circuit in the carburetor and any attempt to play with the mixture control is in vane, in fact, the application of carb heat is probably enough enrichment for a 3,500ft decent (of course, you need to reset the mixture at the new cruising altitude). In my Cub, between 9,500 and 4,000 is less than a ½ inch stroke on the mixture control.

On longer descents, I simply trim the nose down a little, keep the throttle at about 2450 and enjoy the faster speed, I?ll play with the mixture every 3,000ft (or so) until I get to my final mixture setting at my new cruise altitude.

Mixture

Hi Cavy. My carb must be different than yours. If I pull too much mixture at ANY rpm it quits. ??? Jerry.

Thanks, chaps. Useful. I think I need an EGT gauge. Anyone out there disagree and think they're just another useless piece of kit which it is perfectly simple to manage without?

David

I think for your type of flying, an EGT gauge would be most useful. Us lowlanders have less of a need for one, we're leaning purely for economics. But I would think that operating high altitude and out of high mountain and glacier strips would require a little extra finesse...i.e. fine tuning of the leaning procedure to garner maximum output.

Well! I think a cheap way is a manifold pressure gauge. What ever altitude you have if it shows 22" you always ever have the same poweroutput. When I cruise from Fairbanks to Anchorage at 9500´-11500´ I lean to best power and a bit more. At let down I trim the ship nose down with more speed and watch the manifold gauge. When it goes up I throttle back to keep the same indication. So I always have the same power and mixture. To be true I also have a four channel EGT-CHT instrument. But my main control is the manifold gauge.

When at a high density altitude and preparing to take-off. What is recommended procedure for leaning.

Guest:
Do your normal runup, but before you get ready to launch, go to full throttle and pull the mixture until you get to peak rpm (I do it twice to ensure that I?ve got it right) and then enrichen just a tad to keep the motor cool. Go rich to the point that you just start to see the tach (or egt) needle drop off the peak AND NO MORE. Once you?ve lifted off, STAY IN GROUND EFFECT for a while AFTER you?ve gone through Vy, and then rotate and fly the airspeed indicator. You?ll do just fine, but don?t expect your usual runout or climb rate. Density altitude here today was 9,900! I can't wait till it warms up this summer 8)

Be safe

Clay Hammond said:

I think for your type of flying, an EGT gauge would be most useful. Us lowlanders have less of a need for one, we're leaning purely for economics. But I would think that operating high altitude and out of high mountain and glacier strips would require a little extra finesse...i.e. fine tuning of the leaning procedure to garner maximum output.

Click to expand...

I'm a lowlander and I use my EGT all the time. Proper leaning reduces carbon buildup in the cylinders and exhaust system and provides some economy.