Float Guide Issue / Engine Out

[Mike Koerner]

Hi CT’ers,
Only sharing good times lessens the value of this forum… and it’s a bit dishonest. So, I’ll share a recent misadventure. This is a long-winded story. If you’re just interested in the conclusion, you can skip ahead to the last 4 paragraphs.
My engine quit on final several months ago. We had the good fortune of landing fine, and I think we’ve fixed the problem.
My wife and I were on the last leg of a trip to visit my son and his family in Minneapolis. It was a short hop, just 50 miles from Litchfield to Flying Cloud, Minnesota.
It was a cold morning, 14 degrees F. I intended to put tape over the radiator after landing the day before but forgot (error 1). I was reminded of the error while waiting for the engine to warm up. It took forever, even with me cheating a bit on the rpm. I should have taxied back to the tie down area - I carry aluminum-backed tape in the footlocker for just this situation. But I figured it was just a short hop anyway. Eventually the engine got warm enough for the runup. It was running perfectly at that point, so I took off (error 2).
I count to 10 on every takeoff. This one went to eleven. We were off the ground way before my mid-field abort point anyway, but there was a hint of roughness on climb out. I was willing to ascribe this to the cold, but thinking about it later, the oil was at 120 F at that point. The engine runs perfectly at much cooler temperatures than that. I proceeded on course anyway (error 3).
When I tried to level-off I realized that the oil temperature was not going to stay above the 120F minimum operating temperature, even at full throttle. There’s a lot more cooling flow in flight than on the ground, especially at high speed.
But I couldn’t just keep climbing. Flying Cloud is Class D. They expect you to arrive under some semblance of control. Minneapolis Class B is right above it anyway.
I came up with the idea of putting the flaps down to add drag. Well, that didn’t work. To maintain level flight without over-speeding the flaps I had to throttle back. The net result was colder oil.
I had one more trick up my sleeve. I could achieve a high-drag configuration without flaps if I held a forward slip the rest of the way. So, I kicked the right rudder and threw the stick to the left. The engine immediately sputtered and was just about to stop when I instinctively undid the last thing I had done. With the ball centered, the engine came back to life instantly.
Well, that’s not right. Forget the cold. The engine was not running right. I often do forward slips to land, coming in high then kicking out at the last minute to set the wheels on the threshold. The engine has never missed a beat during these maneuvers.
We diverted to the nearest airport, Glencoe. I tried to maintain power during the descent, but there was no way to keep the engine warm on the way down. My wife saw 84 F on the oil temperature at some point. That’s not a problem for engine operation as long as you keep the rpm below 2400, per the manual. I don’t know, but I suspect this restriction is to keep the bypass valve in the oil filter from opening under the high differential pressure that would result from high oil flow and high viscosity.
I usually pull the power to idle on downwind. This time I waited until the turn to base. This put me a little higher than normal, even though it was quite windy. About halfway down the final, the prop stopped very suddenly. There was no sputtering, no warning. It just stopped.
I had the runway made so there was no reason to look for an alternative landing spot or attempt a restart. In fact, I went ahead with a forward slip before touchdown anyway and rolled clear of the runway at the first turnout.
I didn’t relish the thought of pushing the plane the rest of the way to the tiedowns, so I tried to restart the engine. The throttle was already at idle, and the engine was certainly warm enough that it didn’t need the choke. So, all I did was turn the key from “Both” to “Start”. It started instantly and ran perfectly.
Apparently, it was happy on the ground but didn’t like being in the air. That had been true at both ends of this flight.
I was suspicious of a fuel or carburation issue and decided to pull the bowls. The airport has a brand new pilot lounge which was a great place for my wife to wait. I took the upper cowl off, but I was having a hard time working on the ramp in the cold wind.
I asked around and found a kind gentleman, John, who was a member of the local EAA chapter. He let me use his hangar. He and a couple other chapter members stayed to help.
The left bowl was less than half full as I pulled it off, and it was leaking into my hand as I held it. One of the float guides, the vertical rods sticking up out of the bottom of the bowl, was loose (it came out in my hand). The fuel was running out the bottom of the through-hole the guide had been pressed into. I jumped to the conclusion that this was my problem (error 4), remembering a discussion of this on the CT forum and the recommendation that the bottom of these holes be sealed with JB Weld.
John drove me to the hardware store for some JB Kwik Weld, which I applied to all four through-holes.
But thinking about it more I realized that this leak was too slow to affect engine operation. The flow rate from the wings is much higher.
John thought that he had seen some ice in the bottom of the bowl. I was willing to believe this was the problem (error 5). I put the plane back together and did a test flight, including aggressive slips in both directions (within glide of the airport). The engine ran perfectly. I came back, picked up my wife, and we headed on our way, completing the outbound portion of our trip without further incident.
But then again, I hadn’t seen the ice, and there was no water in the gascolator. Furthermore, I run auto fuel with alcohol which dissolves water, unless there is a significant amount, which in this case at least, seemed improbable.
I called Roger Lee. He didn’t think fuel leakage or ice was the problem. He pointed out that the loose guide could allow the float to intermittently interfere with the walls of the bowl or with the fuel shutoff lever, and in uncoordinated flight it could be jammed in one direction or the other. At his suggestion I removed the loose guide and reset it with Loctite 648 retaining compound. The engine ran perfectly on the trip back home.
Apparently, loose float guides are not a common problem. Roger said he had only seen a couple of cases. Also, my 2004 engine is probably older than most, and with 2,450 hours without overhaul, probably had more operating time as well.
With respect to the hours, it occurred to me that the float guide on the other side of that bowl had probably been exposed to a similar vibration environment, and the ones on the other side of the engine couldn’t be much different. So, after I got home, I replaced both bowls. The new design appears to be a different material, much lighter in weight and with a different finish. Also, the float guides are pressed into blind holes and are a little bit longer than the old ones, extending above the rim of the bowl.
I have 35 hours on the new bowls with no further problems.

[FlyingMonkey]

I have had two bowl issues, a couple of years apart.  One was the guide pin leaking like yours, but mine was a steady stream of fuel that was filling the drip tray, pouring over the exhaust and out the bottom of the cowl.  I re-set the pin with the proper LokTite...that's also where I came up with the JB Weld idea.

The second issue was a float that got cocked slightly and hung on the wall of the float bowl.  This caused fuel to gush out the carb inlet, into the airbox, and down the firewall.  This was a LOT of fuel and I discovered it right before takeoff by the fuel smell.

The new revision of the float bowls is sealed at the bottom to prevent the guide pin leaks.  I upgraded to the new bowls and so far have had no more issues.