Engine "Hickup"

duc750sport

duc750sport

Pre-takeoff checklist
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duc750sport
Was flying yesterday (Skyhawk 172N) and after stopping for breakfast I did a full preflight and run up. I was climbing after takeoff and the engine had a major "hiccup".. A feeling like when you're starting to pull the mixture to shut down. I lowered the nose, and the first thing I thought of was carb heat. I applied the carb heat and almost immediately it cleared. I talked to one of my instructors from years ago and he said he doubted it was carb ice that quickly on the climb out. More like water in the fuel that worked it's way through the system, or some other debris. I headed towards the nearest airport and by this time the engine was running fine. My home airport ( a class D) was like 9 nm farther so I opted to head back. The Bravo starts at 3000 here so I entered at 2,999.999999 ft.. :) . Wanted to be high ..Just in case.. I know it could be a handful of things but just wanted to put it out there for any thoughts... I contacted our maintenance and they came out and checked everything and said it was fine, and they found nothing.. Still made the hair on my neck stand up!!
 
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And it does make you sit up and pay attention, doesn't it?

I flew to the Sport Aviation Expo in Sebring. (KORL to KSEF) as I was cruising along the engine hiccuped 3 times in quick succession. It was over before I could pull carb heat or react at all. But I sat up and was REALLY alert for the next several minutes. It never repeated, even on the flight home.

It does get your full attention though.

John
 
It could have indeed been carburetor ice. The fact that carb heat cleared it is a good sign. Still I'd look for other signs (plug fouling, etc...) just to be sure. Settled water should have been caught in the gascolator. Dispersed water generally won't cause "hiccups." Did you look in the gascolator after flight. It holds like three ounces so you'd have to catch a lot of water there.
 
flyingron said:
It could have indeed been carburetor ice. The fact that carb heat cleared it is a good sign. Still I'd look for other signs (plug fouling, etc...) just to be sure. Settled water should have been caught in the gascolator. Dispersed water generally won't cause "hiccups." Did you look in the gascolator after flight. It holds like three ounces so you'd have to catch a lot of water there.
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I didn't check either of those Ron but was told they were checked later in the day and they were ok. The plane had it's annual like 2 weeks ago.
 
jsstevens said:
And it does make you sit up and pay attention, doesn't it?

I flew to the Sport Aviation Expo in Sebring. (KORL to KSEF) as I was cruising along the engine hiccuped 3 times in quick succession. It was over before I could pull carb heat or react at all. But I sat up and was REALLY alert for the next several minutes. It never repeated, even on the flight home.

It does get your full attention though.

John
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Hey John..
It sure did get my attention. Did you ever figure out what your "hiccup" was from?
 
Had that happen in my 182...immediately put it back down and on a ground run up and one mag was suddenly rough...even though it was fine on initial run up. Pulled plugs and a LOT of the bottom plugs were fouled. A&P cleaned all the plugs and I was on my way.

Lots of reasons a "hiccup" can happen but definitely a pucker factor when it does happens...especially on climb out!
 
duc750sport said:
Hey John..
It sure did get my attention. Did you ever figure out what your "hiccup" was from?
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Nope. I've discussed it with the Chief Instructor for the club and the owner. Our best guess is a little water or trash in the fuel system. I sump religiously and have never found any contamination in the this plane.

John
 
Water in a carb bowl doesn't like to go up the main jet. A bead of water can sit in the carb bowl and disrupt fuel flow until somebody drains the bowl. Ingesting water is unlikely. Carb ice is plausable. A carb doesn't ice instantly so it should have been recognizable before the hiccup occurred. I bet you pay more attention from now on. A little isopropyl may be a good idea. I run a dose a couple of times a year whether I need to or not. Water in the fuel is best managed before it becomes a problem.
 
Actually, I've had very rapid onset carb ice. I had mistaken it for an ignition issue (my wife was flying) but upon further reflection I tried the carb heat and it cleared up. This was on a relatively warm day with a pressure carb thought to be fairly immune to icing. It did follow a long period of low power operation.
 
Any chance you sat at idle for a while waiting for your turn to take off?

It sure sounds like carb ice to me. You can collect it on a nice day with high humidity, with low throttle. Full power will cause it to melt and break off in 30 seconds or so, just high enough that a landing right then would suck.

I've had this happen in a 172N as well. It could still climb, so I did and flew a normal pattern. Did a mag check right away and it was fine.
 
MAKG1 said:
Any chance you sat at idle for a while waiting for your turn to take off?

It sure sounds like carb ice to me. You can collect it on a nice day with high humidity, with low throttle. Full power will cause it to melt and break off in 30 seconds or so, just high enough that a landing right then would suck.

I've had this happen in a 172N as well. It could still climb, so I did and flew a normal pattern. Did a mag check right away and it was fine.
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My startup and normal run up time was maybe 5 min or so. Other than the mag check it idles at 1000RPM..
No wait at all once I got to the hold short. Took off right away..
 
The Marvels, SUs, and Strombergs all take whatever is on the bottom of the bowl and present it to the main jet. How can water not get sucked into the engine?

Stewartb said:
Water in a carb bowl doesn't like to go up the main jet. A bead of water can sit in the carb bowl and disrupt fuel flow until somebody drains the bowl...
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duc750sport said:
My startup and normal run up time was maybe 5 min or so. Other than the mag check it idles at 1000RPM..
No wait at all once I got to the hold short. Took off right away..
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That's a very high idle speed for a 172. I expect around 650.

Might not be related, but that points to a poorly tuned carb.
 
MAKG1 said:
That's a very high idle speed for a 172. I expect around 650.

Might not be related, but that points to a poorly tuned carb.
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He probably meant he was idling it at 1000rpm, not that it was set to idle there. Mine idles 6-700, but I usually keep it closer to 9.
 
I meant I set it to 1000RPM's.. Should have been more clear.. It does idle at about 650-700..
 
The C-172C I often fly will idle around 700 but the Chief Instructor/Owner asks that we keep it at 1000 to avoid fouling. (And I lean aggressively as well.) Continental O-300.

The one I had the hiccup in is actually a C-172M with the Lycoming O-320. And I'm quite sure it was not carb ice. I was trimmed and flying along level on a glassy smooth day. If there had been any power reduction prior I would have noticed the need to re-trim. If not water, perhaps a little trash in the carb. It's had no further incidents in 4 more months of flying.

John
 
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