Engine hesitation - Normal?

flyingcheesehead

flyingcheesehead

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iMooniac
Might as well give the whole story...

There were some problems with the engine on the Archer that I fly a lot (club plane). Probably two separate problems, but here they are: 1) The engine hesitates between about 1200-1400 RPM when adding power. 2) Left mag almost always fails the first check.

We had it looked at - They replaced the carb. It sure started a lot easier after that, but it still had the two problems.

Later, it made some metal which showed up as high oil temp and pressure. Changed oil and filter (and noted metal) and watched carefully. Seemed to be OK. Changed oil again about 22 hours later, no more metal.

Then, the plane went on a trip to Sun 'n' Fun. 18 hours and 7 quarts of oil later, we put it back in the shop (it was also not developing full power). Compressions checked good. They removed the #1 cylinder and found a badly worn cam lobe. So, off came the engine and it was sent to Poplar Grove to be fixed.

$10,848.74 later :eek:, We had the plane back. I took it for the first flight. Mag problem still there. First takeoff was OK. Once around the pattern to a full stop and taxi back. Everything looked good, so I went to take off for a cross country (ie break-in) flight. This time, I aborted the takeoff because the engine hesitated big-time and didn't recover like normal, it just kind of sputtered and groaned its way up. Abort, taxi back, full-power runup and everything seemed normal. So, I took off again and it was OK. I flew for about an hour and landed, shut down and went inside to grab a drink.

On the return flight, the same thing happened: I aborted the takeoff, taxied back, did a full-power runup which worked fine, and took off again and flew back to the home drome.

Back into the shop. This time, they replaced the carb (again), the muffler (one of the baffles had collapsed, causing a partial blockage), and the left mag (burned points).

You might think it'd be OK after all that, but... Still has the hesitation when adding power and the left mag still sometimes fails the first check. :dunno:

We ferried it over to RYV for its annual only a couple of weeks later. While flying our other Archer back, I noticed two things: 1) the other Archer's engine runs much smoother, 2) The other Archer has the very same hesitation between 1200-1400 RPM when adding power! :dunno:

Is this hesitation normal? (Lyc O-360-A4M IIRC) What could be causing it? Why does the left mag seem to fail the first check so often, could it be something I'm doing, or something in the system besides the mag itself?

Thanks in advance for any ideas!
 
Kent, neither the mag check or the hesitation sound normal to me, Kent. In the 3 or 4 years I've owned my Archer II, it has never failed a mag check. Ditto on the hesitation -- I get a smooth increase in power.

When I was learning to fly fixed-wing, the club had an Archer II which had a hesitation problem, which caused a burp as you pushed the throttle forward for takeoff. The explanation supposedly was a faulty accelerator pump (which to my knowledge was never fixed in that a/c). As you bring in throttle, the pump, as I understand it, is supposed to squirt in extra gas into the carb so you get a smooth increase in rpm.

You didn't say whether you lean aggressively on the ground -- if you are not then the mag check problem might be plug fouling.
 
Sounds like a mixture problem of some sort to me. As mentioned above - are you leaning during ground ops? What kind of air temps/D.A. are you guys having right now? When the engine hesitates, does it sound like a 'dry' or 'wet' hesitation - such as too much fuel or not enough fuel during acceleration?

-Chris
 
flyingcheesehead said:
Might as well give the whole story...

There were some problems with the engine on the Archer that I fly a lot (club plane). Probably two separate problems, but here they are: 1) The engine hesitates between about 1200-1400 RPM when adding power. 2) Left mag almost always fails the first check.

We had it looked at - They replaced the carb. It sure started a lot easier after that, but it still had the two problems.

Later, it made some metal which showed up as high oil temp and pressure. Changed oil and filter (and noted metal) and watched carefully. Seemed to be OK. Changed oil again about 22 hours later, no more metal.

Then, the plane went on a trip to Sun 'n' Fun. 18 hours and 7 quarts of oil later, we put it back in the shop (it was also not developing full power). Compressions checked good. They removed the #1 cylinder and found a badly worn cam lobe. So, off came the engine and it was sent to Poplar Grove to be fixed.

$10,848.74 later :eek:, We had the plane back. I took it for the first flight. Mag problem still there. First takeoff was OK. Once around the pattern to a full stop and taxi back. Everything looked good, so I went to take off for a cross country (ie break-in) flight. This time, I aborted the takeoff because the engine hesitated big-time and didn't recover like normal, it just kind of sputtered and groaned its way up. Abort, taxi back, full-power runup and everything seemed normal. So, I took off again and it was OK. I flew for about an hour and landed, shut down and went inside to grab a drink.

On the return flight, the same thing happened: I aborted the takeoff, taxied back, did a full-power runup which worked fine, and took off again and flew back to the home drome.

Back into the shop. This time, they replaced the carb (again), the muffler (one of the baffles had collapsed, causing a partial blockage), and the left mag (burned points).

You might think it'd be OK after all that, but... Still has the hesitation when adding power and the left mag still sometimes fails the first check. :dunno:

We ferried it over to RYV for its annual only a couple of weeks later. While flying our other Archer back, I noticed two things: 1) the other Archer's engine runs much smoother, 2) The other Archer has the very same hesitation between 1200-1400 RPM when adding power! :dunno:

Is this hesitation normal? (Lyc O-360-A4M IIRC) What could be causing it? Why does the left mag seem to fail the first check so often, could it be something I'm doing, or something in the system besides the mag itself?

Thanks in advance for any ideas!
Click to expand...

Sounds to me like your mech doesn't know how to adjust the carb accelerator pump to add the proper amount of fuel/
 
I would check the idle circuit mixture. My understanding is that if it is set to lean, the engine will stumble when speeded up from an idle. This is a needle valve type screw on the back o fthe carb (on an O-320). If it is set correctly, the engine is supposed to speed up around 50 RPM before dying when you go to idle cut-off to shut it down. There are also normally multiple holes in the linkage for the accelerator pump. Putting the link to the piston into various holes makes its either move more of less for the same amount of throttle movement. (Not an A&P)
 
It’ not normal! I would do two things.

1. Remove magneto and sent to a repair station for complete check. They will put it on a test bench and run it up if it fails overhaul it.
2. I believe your carburetor is not set properly or it has a problem with the throttle bushing being loose (even new). A certain manufacture has a problem and I have spoken to them about it. They have replaced several carburetors then sent a Rep. Found the bushing were undersize (OPPS).

Just one man’s opinion. A&P/IA

Stache
 
My Cherokee 180 does the same thing, re the hesitation. Its a bit weird to feel it hesitate (same RPM range, btw), but I've gotten used to it. I have had it checked by numerous A&Ps and all have said its a Cherokee thing. I dunno.
 
CJones said:
What kind of air temps/D.A. are you guys having right now? When the engine hesitates, does it sound like a 'dry' or 'wet' hesitation - such as too much fuel or not enough fuel during acceleration?
Click to expand...

The problem has occurred from -20F all the way up to 90F. I'd call it a "dry" hesitation, but I can't be absolutely sure.

Sounds like the accelerator pump is a suspect in many of the great minds here... I'll mention it to our MO.
 
Graueradler said:
I would check the idle circuit mixture. My understanding is that if it is set to lean, the engine will stumble when speeded up from an idle.
Click to expand...

When advancing the throttle smoothly, it speeds up from idle smoothly (well, 1000 RPM's that is - But no hesitation earlier on when I go from idle to 1000 either). It isn't until around 1200-1400 RPM that it stumbles.
 
RotaryWingBob said:
You didn't say whether you lean aggressively on the ground -- if you are not then the mag check problem might be plug fouling.
Click to expand...

Yes, I lean on the ground. (master, mixture, tank, pump, prime, clear, start, oil pressure, lean <-- my starting checklist)

However, I can't speak for the rest of the club. :dunno:

Edit: Also, I don't know why the left mag would miraculously fix itself? I do the check left (both), right (both), left (both) and it always seems a bit sluggish on the first turn to the left mag but then it's fine the second time around. Color me confused.
 
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SkyHog said:
My Cherokee 180 does the same thing, re the hesitation. Its a bit weird to feel it hesitate (same RPM range, btw), but I've gotten used to it. I have had it checked by numerous A&Ps and all have said its a Cherokee thing. I dunno.
Click to expand...
I don't buy that, Nick, that it's a Cherokee thing. Out of about a dozen Cherokees I've flown, including 180's, 161's, and 181's, I've only experienced the hesitation problem with a single 181.
 
ive never experience this problem on cherokees.
 
Yhe hesitation sounds to me like it has a 10-3878 carburetor on it. This is a bit too lean for some but not all O-360's. It can be rejetted to the 10-5193 spec. You have not said in what manner the left mag "fails" the check. Since the mag has been serviced I might start to suspect a p lead or switch problem. Charlie Melot Zephyr Aircraft Engines
 
Tony, maybe you can take a looksee when we go flying to see if maybe I'm imagining the exact same problem that Kent is talking about. Its pretty noticeable when, for example, trying to go around.
 
okie dokie. now on some of those engines, there is supposed to be a placard, something like "no less than 3 seconds from idle to full power" as quick throttle changes can cause the engine to cough and do generally uncomfortable things for the pilot. this could be whats happening to you.
 
tonycondon said:
okie dokie. now on some of those engines, there is supposed to be a placard, something like "no less than 3 seconds from idle to full power" as quick throttle changes can cause the engine to cough and do generally uncomfortable things for the pilot. this could be whats happening to you.
Click to expand...

Huh. Awesome. There's no placard, but that sounds like that could be it. I am a notorious throttle jammer :D.
 
I messed up an RC airplane that way, real hot humid day, approaching my road to land, approach all messed up, I decide "hey im smart, ill go around" run the throttle to full really fast and *cough cough putt silence* "aww %&$#" says me. try to glide it. clip the trees on the side of the road, stall it into the ditch. I managed to put some packing tape over the dent in the wing and keep flying that one though. see you this afternoon
 
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