Engine hesitation ~1500 Piper Archer II

The Marvelous Dribbler series of carbs are just barely carbs. They have numerous shortcomings, and this is one of them. My 68-year-old Stromberg behaves better than that, and better than most of the MS carbs I've maintained.

Try some carb heat to enrich the mix at low settings.
 
Every Warrior and Archer I rent has this issue, I've just learned to live with it.
 
Henning said:
Look up Harrison Ford's Ryan crash and cause...
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The main jet rattled out of its threads and instantly flooded the engine. There wasn't anything in between running normally and quitting altogether. Doesn't bear much resemblance to the current issue.

We had an O-320-A2D in a Citabria that did this. I was never able to stop it. It would hesitate when applying power after a glide. Two different shops rebuilt the carb, and aother rebuilt the mags, and I eventually replaced both mags. None of it changed anything. It was just a habit of some of the -A series engines. All I could find on it was some suspicion by some engine people that the intake plenum in the sump has some oddity about it that causes it to accumulate liquid fuel at low power settings (and therefore low manifold airflow) as the atomized fuel strikes the plenum walls and coalesces and puddles. Opening the throttle sucks this liquid fuel in and momentarily floods the cylinders and causes the hiccup. We could sometimes see a puff of black smoke if a pilot aborted a landing and opened the throttle in the flare.

Fooling with the carb wouldn't change that. Exchanging the whole engine might. STCing an injected engine into the airframe would change it for sure.
 
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Dan Thomas said:
The main jet rattled out of its threads and instantly flooded the engine. There wasn't anything in between running normally and quitting altogether. Doesn't bear much resemblance to the current issue.

We had an O-320-A2D in a Citabria that did this. I was never able to stop it. It would hesitate when applying power after a glide. Two different shops rebuilt the carb, and aother rebuilt the mags, and I eventually replaced both mags. None of it changed anything. It was just a habit of some of the -A series engines. All I could find on it was some suspicion by some engine people that the intake plenum in the sump has some oddity about it that causes it to accumulate liquid fuel at low power settings (and therefore low manifold airflow) as the atomized fuel strikes the plenum walls and coalesces and puddles. Opening the throttle sucks this liquid fuel in and momentarily floods the cylinders and causes the hiccup. We could sometimes see a puff of black smoke if a pilot aborted a landing and opened the throttle in the flare.

Fooling with the carb wouldn't change that. Exchanging the whole engine might. STCing an injected engine into the airframe would change it for sure.
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Have you ever heard the term " Clearing the engine" old timers knew how to do that.
 
Tom-D said:
Have you ever heard the term " Clearing the engine" old timers knew how to do that.
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Heck, I think it is even written into the PIM. Mine says:
"Descent:
Every 1500 FT, apply engine power to prevent excess cooling and spark plugs fouling."
The instruction does not address pooling of liquid fuel, but you get the picture. Clear the engine at low power.

That said, I still think he should look and see which carburetor he has.
 
Fuel pooling could be caused by an incorrect gasket where the carb is mounted to the intake manifold spider. I understand there is almost always a combination of liquid fuel and atomized fuel flowing thru the intake system. True vaporization which is necessary for combustion, doesn't occur until there is heat of compression.

That's why I'd look for some sort of pooling spot in the intake manifold.
 
Tom-D said:
Have you ever heard the term " Clearing the engine" old timers knew how to do that.
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Yup, and when I was flying it I would do that. However, it was a training airplane, one of a fleet of seven Lycomings, and none of the rest had this issue. When teaching students it's difficult enough without having to introduce special treatments for one airplane; they're busy enough learning to fly the taildragger without having to babysit an engine that has a bad habit. We were already teaching that you clear the engine every 1000 feet or sooner on forced approaches or long glides, not only to get the manifold cleared but to get some heat in the carb. The exhaust system gets cooled off and carb ice can build silently and the engine could refuse to respond in an undershoot or aborted approach.
 
nrpetersen said:
Q - To the OP - Does it still hesitate if carb heat is ON thru the throttle change? This might suggest if it is experiencing a temporary lean or rich mixture. Carb heat will normally richen a steady state mixture in a calibrated carburator.

Another cross check - is it worse or better on cooler/dry days?
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Well it's happened maybe 2 or 3 times and only happened just under 1500 rpm and only just bumping the throttle up slightly for a 100rpm increase. Ideally I don't even add power while landing so not sure. Haven't tried carb heat or playing with the mixture either way. I have recently moved farther south and am flying in warmer weather, I can see that making a difference.

Has never done it when applying power for takeoff/runup/any other circumstance.

We're talking about a stumble or cough here so brief the first time I wasn't even sure if it really happened. Engine doesn't quit, just drops maybe 200RPM just for a fraction of a second. It sounds a lot like the common piper stumble or whatever term you want to use that other people are describing.
 
Mine did this rather slightly, until a carb IRAN in which we discovered that the throttle plate shaft was worn and loose in the bearings. After that and a mixture adjustment, I never got the hesitation that the op describes.
 
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