Comments on: Diagnose this: rough engine on approach

By: Chris Tapp

Chris Tapp — Thu, 23 Apr 2015 23:59:38 +0000

I knew this because the same thing happened to me when I had a Cherokee 🙂
Always triple checked it was tight after that..

By: Frank Ch. Eigler

Frank Ch. Eigler — Mon, 13 Apr 2015 17:27:25 +0000

David, do you have an engine monitor widget in the plane? Is a slow leaning part of your runup (the extra fuel could’ve shown up as a larger rpm rise / later drop than usual)?

By: David Megginson

David Megginson — Mon, 13 Apr 2015 11:24:15 +0000

In reply to ptomblin. Me neither. I figure it must have been right on the edge of being locked — either I turned it too far, or not far enough.

By: ptomblin

ptomblin — Mon, 13 Apr 2015 11:15:56 +0000

I’ve forgotten to lock the primer after starting (which shows up in the run-up) but I’ve never had it open in flight.

By: David Megginson

David Megginson — Mon, 13 Apr 2015 11:14:06 +0000

In reply to douglasr. @douglasr is correct — the primer knob had simply popped very slightly open. I usually verify it in my pre-landing checks, but since the roughness started *before* then (when I initially cut power for descent), I was distracted planning a high glidepath (so that I could make the runway in case of complete engine failure), and didn't pull to verify that the primer was locked.

By: douglasr

douglasr — Mon, 13 Apr 2015 05:27:01 +0000

Carb ice is the go to answer (unless of course you’re fuel injected), until you mentioned the engine not stopping. If mixture idle cutoff doesn’t work then fuel is entering the system from somewhere. I’d have to check the POH to be sure but obvious sources are mixture control (cable broken or stuck at some position), the primer (stuck open) or the carburetor itself. Regardless, I’m guessing that at higher RPM that the excess fuel wasn’t that noticeable since the engine is consuming close to max as it is but at lower RPM one or more (but obviously not all) cylinders were being flooded, causing the rough running. If I had to hazard a guess, if say the carburetor since if it was the primer leaking you should have experienced roughness during taxi, which presumes that the primer broke during start up.

By: Nop

Nop — Mon, 13 Apr 2015 04:45:58 +0000

Per my G+ comment; I’m guessing gunge or bad seals in the carb.

By: David Megginson

David Megginson — Mon, 13 Apr 2015 00:33:53 +0000

In reply to Paul Tomblin.

That was our first guess chatting on the ramp, but it had two (apparent) strikes against it:

– carb ice wouldn’t (AFAIK) explain the engine still running at full lean
– carb ice is rare in the Warrior, because the air intake is right next to the muffler, which heats the air by default

By: Paul Tomblin

Paul Tomblin — Mon, 13 Apr 2015 00:28:41 +0000

Carb ice?