Stutter on power reduction

SixPapaCharlie

SixPapaCharlie

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POH says mixture rich. Feedback from the Grumman group (Although this is not Grumman specific) is I should not always go mixture rich when landing.

Tonight Density altitude was ~4k feet

Downwind, reducing RPM from 2600 to about 2100 and it boggs down as though I pulled power. This lasts about 1 legit second and then it resumes.

I have had what I would describe as a hiccup or stumble during this power reduction on my last Lyc 320 almost like a single misfire and I have experienced that on this engine as well.

1. Should I remain lean? Does it sound like too rich briefly?
2. What exactly mechanically is happening that causes this?

I don't like it but all my searching turns up that it is a common experience.
Runup is fine / no apparent plug fouling detected on mag check.


Thanks in advance.
 
Ponder this. Full rich in November is not the same as full rich in July. If your engine is set up properly it'll supply adequate fuel in cool temps. You wouldn't expect to use the same fuel settings in hot temps because equal for equal the hot temps will be make that mixture rich. Why not try leaving it reasonably leaned and see what happens?
 
Stewartb said:
Ponder this. Full rich in November is not the same as full rich in July. If your engine is set up properly it'll supply adequate fuel in cool temps. You wouldn't expect to use the same fuel settings in hot temps because equal for equal the hot temps will be make that mixture rich. Why not try leaving it reasonably leaned and see what happens?
Click to expand...

I am going to do that next go round. Lean in cruise and just enrighen a bit as I come down but not fully rich.
The POH says full rich but I am going to leave it out a bit next few flights and see the difference.

Can this "too rich" stumble thing actually kill the engine? That is my underlying concern.
It is startling when it happens.
 
Make it quit? Probably not, but it may run like a turd when you need to go-around. Remember, carb heat enriches the mixture, too.
 
In my 91 Tiger (0-360), I used to go full rich during the approach because that's what the POH says and encountered some of the same symptoms as you describe especially as I reduced power. I no longer go full full rich and depending on the cruising altitude, I may not enrich during the approach at all. The engine seems to run smoother, especially at around 1400-1500 rpm and the engine monitor shows good EGT's and CHT's. If I need to go around, it takes but just a second to go to full rich.
 
Okay, thanks for the tips. I'll go up tomorrow and leave it lean and see what is different.
I am taking my kids up for the first time in the new plane Saturday morning so I am feeling really cautious.
 
I knew one old Skyhawk that would blubber and die at full rich at this altitude. It was misadjusted.

It's rare that I'll go full rich up here in the 182 -- it'll blubber and carry on like me with a head cold.

At 4000' DA I would expect it shouldn't be quite as blubbery or complaining as much.

But like you've said, fly it where it likes to be and just make sure you get it forward in a go-around. Smooth engine is happier than rough engine.
 
Hot and high DA, 2100 rpm is off the bottom of your power table, probably under 50% power? Keep it leaned. Also, how quickly do you reduce rpm?
 
GeorgeC said:
Hot and high DA, 2100 rpm is off the bottom of your power table, probably under 50% power? Keep it leaned. Also, how quickly do you reduce rpm?
Click to expand...

I am pretty gentle with power changes. Probably a 3 count from 26k to 21k

What is a power table? Where do I find mine?
 
there's a good thread on this in mooneyspace, I'll see if I can find the link. basically, everyone points to "you should have bought a cirrus".
 
Rich burble when you pull the power? Hardly a surprise - u be rich to start with plus you get extra fuel flashing off the manifold walls.

Some of these guys are against the rev limiter, but watch the car going into the corner at 1:02
 
It's a temporary rich condition on power reduction. That happens in the Arrow sometimes - not a stutter, but it backfires if I reduce the power too quickly.
 
Think of what and why you're doing what you're doing, use logic.

Full rich when it's a high DA doesn't make much sense does it?
 
I was reading troubleshooting for what I think is your carb and it was suggested that the accelerator pump was the problem and to replace the plunger.
 
I had a lesson on this when I was in training. Around 70 degrees one day, light rain which "can" be icing conditions and DA was around 4000'. I was going to do a touch and go at full rich, carb heat on. I touched down, clean the airplane up and pushed the throttle forward. Imagine my surprise when nothing happened but a bunch of black smoke exiting the exhaust pipe (according to the guys on the ground). I thought I'd broken the throttle cable.

I've since learned to lean until the engine is happy at all power settings, temps and density altitudes and keep it leaned.
 
SixPapaCharlie said:
POH says mixture rich. Feedback from the Grumman group (Although this is not Grumman specific) is I should not always go mixture rich when landing.

Tonight Density altitude was ~4k feet

Downwind, reducing RPM from 2600 to about 2100 and it boggs down as though I pulled power. This lasts about 1 legit second and then it resumes.

I have had what I would describe as a hiccup or stumble during this power reduction on my last Lyc 320 almost like a single misfire and I have experienced that on this engine as well.

1. Should I remain lean? Does it sound like too rich briefly?
2. What exactly mechanically is happening that causes this?

I don't like it but all my searching turns up that it is a common experience.
Runup is fine / no apparent plug fouling detected on mag check.


Thanks in advance.
Click to expand...


I'm not a fan of the knee-jerk, checklist-calls-for-it approach. Leave the mix alone and the engine will tell you when it needs a richer mixture.,,then enrich only enough to regain smooth operation. The only rationale for the full-rich-on-final procedure is the potential for a go-around. Being a fairly sane person I consider myself capable of going to full rich on a go-around IF NECESSARY without doing it in advance.

Bob
 
I think the bigger issue is that POHs assume standard day conditions, not near-100* Texas evenings. You gotta adjust for conditions.
 
bobmrg said:
I'm not a fan of the knee-jerk, checklist-calls-for-it approach. Leave the mix alone and the engine will tell you when it needs a richer mixture.,,then enrich only enough to regain smooth operation. The only rationale for the full-rich-on-final procedure is the potential for a go-around. Being a fairly sane person I consider myself capable of going to full rich on a go-around IF NECESSARY without doing it in advance.

Bob
Click to expand...

Same with me. In flight training I was taught to be full rich under 3000 msl. Common sense and listening to the engine taught me otherwise.
 
Let me add this question. What is the purpose of adding carb heat on downwind?

This is another of those handbook calls for it and primary instructor and forced it. I'm back in a plane with carb heat for the first time after 3 years and I don't see a reason really to touch it especially this time of year
 
SixPapaCharlie said:
Let me add this question. What is the purpose of adding carb heat on downwind?

This is another of those handbook calls for it and primary instructor and forced it. I'm back in a plane with carb heat for the first time after 3 years and I don't see a reason really to touch it especially this time of year
Click to expand...

Mainly to avoid carb ice post power reduction so you can go around if you have to. With the humidity what it is here in Florida you can get carb ice in some surprisingly high temp conditions. And secondarily to build good habits for when ice can form.
 
...and you do it (add carb heat) on downwind because the engine is still producing enough power to melt the ice. On final you are very close to idle.
 
90F and 60% RH is not uncommon around here...

carb-ice-potential-chart.jpg
 
Kiddo's Driver said:
Why would the accelerator pump come into play on a power reduction?
Click to expand...

The troubleshooting guide I was reading I believe for the OP's carburetor stated that fuel leakage past the plunger to the other side and fuel being forced out the vent can cause hesitation or the engine to quit when decelerating.
 
AKBill said:
The troubleshooting guide I was reading I believe for the OP's carburetor stated that fuel leakage past the plunger to the other side and fuel being forced out the vent can cause hesitation or the engine to quit when decelerating.
Click to expand...
Can I get a copy?
 
SixPapaCharlie said:
Can I get a copy?
Click to expand...
Sure I will try to PM you. I also have an O320 in my plane its an O320-E3D. Not sure what you have but I will forward what I have. I have never had a stumble or hesitation as you describe. Of course altitudes and temps were we fly are way different. I'm at sea level and temps here in the summer don't get much higher that 70F normally in the mid 50's to mid 60's.
 
SixPapaCharlie said:
Let me add this question. What is the purpose of adding carb heat on downwind?

This is another of those handbook calls for it and primary instructor and forced it. I'm back in a plane with carb heat for the first time after 3 years and I don't see a reason really to touch it especially this time of year
Click to expand...

Others have covered the reason for the carb heat.

The other thing to remember is applying carb heat usually makes the mixture richer without touching the mixture knob, too.

Carb heat plus full rich on the mixture control simultaneously is a LOT richer if the engine was running fine and was leaned per manufacturer's recommendations at 1000' AGL in the pattern.
 
Keep in mind that by pulling the carb heat all the way out, you're enriching the mixture even more if you're already running full rich, since that warm air is now funneling into the carb. This will in-turn cool the engine and create a lower exhaust heat, which ultimately means a cooler carb heat application.

To get the biggest bang for your buck and allow the warmest heat to enter the carburetor, than keeping a lean(er) mixture is ideal. Most people don't think about leaning the mixture prior to applying carb heat, and by not leaning, you don't get as much carb heat as you could have had and you're engine will not produce as much power as it otherwise could make, with carb heat applied. Of course this only works during certain ambient conditions, such as now during the hot summer months. In the winter, it's not as much of a problem. Just something to gnaw on now that you're coming back into the carbureted world.
 
Any of y'all go carb heat off on short final for max power and have filtered air once you're back on the dirty earth?
 
At 5000 AGL with a planned decent of about 8 minutes I will actually reduce throttle a bit then lean mixture even more till it starts to misfire. Then apply some carb heat to smooth it out and man does it burn very little fuel on approach and landing (O-320 with fixed pitch)


Gets down to about 4 gallons per hour at 500 feet per minute decent rate without touching pitch trim. Kinda fun to play with
 
bnt83 said:
At 5000 AGL with a planned decent of about 8 minutes I will actually reduce throttle a bit then lean mixture even more till it starts to misfire. Then apply some carb heat to smooth it out and man does it burn very little fuel on approach and landing (O-320 with fixed pitch)


Gets down to about 4 gallons per hour at 500 feet per minute decent rate without touching pitch trim. Kinda fun to play with
Click to expand...
Going to try this.
 
James331 said:
Any of y'all go carb heat off on short final for max power and have filtered air once you're back on the dirty earth?
Click to expand...

Probably should, but lazy. Not to mention that "filter" on the front of a 182 isn't much to write home about when it comes to dirt. It's not very effective. Thing looks like it's made of the same stuff as a dollar store scrubby pad. LOL
 
denverpilot said:
Probably should, but lazy. Not to mention that "filter" on the front of a 182 isn't much to write home about when it comes to dirt. It's not very effective. Thing looks like it's made of the same stuff as a dollar store scrubby pad. LOL
Click to expand...
You got something against dollar store scrubby pads?
 
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