Engine Issue during Climb - Help!
Hi All, this is my first post and it's a doozy...

I own a 162 Skycatcher LSA which has been a great plane until the last year.  Since the last annual in December 2019, it has had a problem with sputtering/hiccuping/momentary loss of power on take off.  The best way to describe it is that it's like instantaneously dropping the power to idle and then it going back to full power.  Happens in a second or less so it's hard to tell what is happening with engine when it happens.  In general, the plane doesn't feel like it has the power it once did.  It has happened 4 times so far and only happens in a climb attitude at full power.  Also, it seems to happen near pattern altitude and has never happened during level flight at cruise power.

My local A&P has checked for water in the fuel (none found), replaced a drain line from the airbox, sent the carburetor out for inspection (minor adjustments but all good), and in the process of all this found a sticky exhaust valve (sputter has happened since fix).  I've talked to a couple other A&P's and they are stumped.

Obviously, my flying time has been severely curtailed, blood pressure elevated, and confidence in the aircraft is at an all time low.  Not to mention, I have my flight review next month and may not have a plane to have it in.

If anyone has heard of this before or has any ideas for troubleshooting, I'm all ears.  Any help or feedback is greatly appreciated!
6 Replies
I know this is a little off the norm, but so is your problem. Years ago, a farmer bought a new tractor.  The tractor would run fine then stop running for no apparent reason. The shop completely tore the fuel system down and replaced everything in it, but the problem persisted. Finally they took out the fuel tank and found a dead cockroach that was floating in the fuel then getting sucked over the fuel line when the engine was running. You might have a similar problem of debris in your tank.
The original FAR 23 standard for fuel flow on gravity aircraft was 150% of the take off fuel flow at the take off attitude.  With the tank at 1/4, secure the tail to the floor, and remove the Carburetor fuel line and allow fuel to fill a graduated container for 1 minute (longer for accuracy).  Lets use round numbers, 10GPH take of fuel flow would require 15 GPH in this test.  Divide that by 60 and you end up with a quart (.25 gal) per minute.   This simple test will validate all of the potential problems.  One final thought, to better simulate the problem, sample for 4-10 minutes.  

Fun facts, as fuel level decreases, head pressure decreases, and fuel flow decreases.  When the fuel flow becomes less than 150%, the rest becomes unusable fuel.  The C172 does not have an electric fuel boost pump, the C172XP with the 180 HP motor does.  Take off fuel flow could not be met for the whole tank.  
Hi Jim,

Thanks for the feedback!  

Yes, this is only happening at high pitch attitudes.  I have not seen any indication at level flight or run-ups.  All the compressions were good at the last annual and that was only 10 hours ago.

My A&P was suspecting the carb float as well.  He is still questioning at this point.  I talked to him on Friday and he was looking to replace it, at least temporarily, to see if the problem went away.  He's also changed the ignition switch as he's seen issues where carbon tracking in the switch has caused issues with both mags at once.

I haven't had multiple occurrences happen except the first time it happened.  One happened on climb out and then when I turned crosswind, it happened again still at a climb.  Once I leveled out and reduced power, it didn't happen again (on that flight).  I'll try to do what you recommended about leveling out but it happens so quickly, I'm not sure it would tell us anything.  These events last no more that a second or two at the most.

I'll ask the A&P about the fuel flow.  I was thinking that myself but it doesn't seem that it would be so momentary if it was flow,  The shut off valve is a push-pull lever like the throttle. There is no difficulty in operating it but it is probably worth a check to make sure it is functioning properly.  No fuel pump in the 162, only gravity feed.

The magnetos are Slick 4300 series.  All mag checks have been good.  Hours on the mags are 885. My A&P didn't think it was a mag specific issue as one could drop and you wouldn't know but said the ignition switch ties them together and if there was a short there, it could drop both mags at the same time.  That's why he changed out the ignition switch.  I'll ask him about the mag grounding.

Someone else had mentioned the carb heat door as a possible issue.  I'll take a look and see if I can determine anything with the carb heat door.  Could that cause more than the typical carb heat RPM drop?

Thanks again!

Good morning Kevin,

Let me begin by saying that I have never worked on a Skycatcher, so my comments and questions will be derived from the 150/152.
This is only happening at high pitch attitudes, right?  No abnormal indications in level flight or on ground run-ups?  I am assuming the compression tests are good.

Air & Fuel in the right ratio and Ignition at the right time.  That is what is needed to make any engine run.  The pitch attitude is the key to solving this problem.  That is unusual, and I would suspect the carb float, but you said the carb checked good.

I agree with Daddis that a fuel line obstruction could cause a power loss, although it is unusual for engine output to immediately return to full power.  Fuel restricted engines usually stumble their way back up to power due to overly lean mixtures as the fuel line fills back up.  Does the engine recovery lead to an immediate recurrence of the loss?.  If the loss occurs again, leave the throttle alone and reduce pitch attitude to see if the engine smooths out.  Does this engine do this at high pitch at higher altitude or only pattern altitude?
Look and see if the 162 has a "finger screen" type fuel filter in the fuel lines from the tanks.  The 150 has one that protrudes into each tank (a total of two on the 150), located at the wing root panel just above each door.  The finger screen looks like a regular union fitting, but when the fuel line is disconnected and the fitting is unscrewed from the tank, there is a coarse mesh strainer on the part that protrudes into the tank.   It would be unusual to find this plugged, but it is there for a reason, so Cessna apparently thinks it could happen.   I have seen one collapsed in on itself.   Obviously, the aircraft would need to be completely de-fueled to safely remove the finger screens.
Is the fuel shutoff valve hard to turn?  If it is, it needs to be disassembled and inspected (again, de-fueled).  (Piper airplanes are bad about this, and have a Service Bulletin to lubricate the valve plug to prevent the interruption of fuel flow.)
The 162 does not have a fuel pump, correct?

What is the magneto manufacturer?  The mag drop checks are good on the ground?  Approximately how many hours are on the mags?  (Most mags will operate well beyond the 500 hour inspection.)  I know of no un-pressurized mags that have issues with grounding out at high pitch attitudes.  For the mags, disconnect the P-leads from the mags (CAUTION-hot mags!) hook up a multimeter to the leads and set it up for continuity testing (beep when there is continuity to ground), turn the mags on and ensure that the tester beeps (grounded through the mag switch).  Turn off the mags and ensure the tester stops beeping, then wiggle the wires from the mag switch to the mags and see if one of the P-lead wires is grounding out to the airframe.  Disconnect the tester and reconnect the P-leads.  This test should confirm that you do not have a P-lead wire chafed to ground and making contact only at high pitch attitudes and thus, killing one mag for a brief period.  It's not very likely, but worth checking.  I would not suspect moisture buildup in the mags because that should show up on the run-up checks.

If the engine has carb heat, take out the induction air filter and move the carb heat control to ensure that the damper moves when commanded, but doesn't flop around when not commanded.  If the damper does move on its own, it could cause a rapid power loss.  The carb heat box has caused problems many times in the life of the 150 series.

I hope this helps,

Thanks Daddis.  One of the A&P's I talked to did mention he thought it could be a fuel restriction either in the line or the gascolator.  The other A&P mentioned magneto timing or a possible issue with the magneto(s) in general as they never had a 500 hour inspection.  I'll run your list by my local A&P and see what he thinks.  Thanks again.
Any internal combustion engine needs three components to operate properly and smoothly - 1. a steady flow of fuel, 2. a constant ignition source, and 3. uninterrupted air flow. A few suggestion since you note it only happens at full power - check that the fuel supply line to the carb is not bent, kinked, dented, or partially obstructed. Check fuel filters for obstructions. Check that the spark plugs are clean, electrodes not too worn, gapped properly, and are of the proper heat range for the engine. Check plug wires for defects and magnetos for timing. Check that the air filter and air intake tube(s) are clean and unobstructed. This is top level but as you didn't mention any of these, they bear checking.