O-470r running rough

Whitewaterraftr

Whitewaterraftr

Filing Flight Plan
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Kyle wood
New to the forum, this is my first post. I have a 182A tail wheel. Flying over oregon yesterday it started running rough, pushed the mixture in, no change, checked carb heat, nothing but a power loss. Mag check, not much change, fuel on both no change. Messed with throttle, not much of a change. Got it on the ground in Monument, OR.

On the ground I did a runup. At 23"/23 full rich its flowing 13 gph. From memory, it should be more than that. I flew it again, left it firewalled and climbed to 23", fuel flow was around 16 I believe.

If I'm at a lower altitude and pull the throttle back to 23" it still only flows 13gph full rich. Pulling the mixture back the slightest and it will run rough. Before this it would run with the mixture pulled out one knuckle.


Any ideas? Checked mixture cable at the carb and its right. Unhooked fuel hose from the carb and it will flow 46 gph free flow.
 
If you’ve been exposed to cool temps? Add isopropyl to your fuel. A few drops of water in the carb bowl will interfere with fuel flow. Isopropyl is easier than draining the bowl, but if you want to be sure, drain the bowl and capture the fuel to check for water. I use isopropyl in winter to avoid what you’re seeing.
 
I didn't find so much as a drop off water in either tank, the gascolator or the carb bowl.
 
I flew it back to Washington and didnt find any water in it when I got there either.
 
Check the easy stuff, plugs good? Ignition leads? Time & years on the engine? Annual soon?
 
3 hours after it was annualed. Plugs are good, 1600 tt, probably 25 years in the engine. Borescope has been done, verything looks great. I found a little junk in the fuel screen on the carb but not enough to cause a problem.
 
Plugs, air filter, magneto timing. Engine monitoring data is useful as well if you have it.
 
No engine data other than fuel flow. Plugs, filter and mags look good. Fuel flow at 23" is only 13 full rich, that can't be right, can it?
 
Whitewaterraftr said:
Flying over oregon yesterday it started running rough, pushed the mixture in, no change, checked carb heat, nothing but a power loss.

Checked mixture cable at the carb and its right.
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How long did you leave the carb heat on? You won't get instant improvement. It takes time, and some more shaking and maybe further power loss, before the ice is out.

Are you sure that the control is rigged right and that neither the wire clamp or the housing clamp are not slipping? That the carb's mix lever is on its shaft correctly and properly tight?
 
Induction leak could explain it. All rubbers were new about 200 hours ago.

Everything to do with the mixture control is right.

I can still repeat the problem at 23" at lower altitude.
 
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Any idea what an manifold pressure a o470 should idle at?
 
From OP’s first description it sounds like it is running lean. An engine should always be at least slightly rich throughout the flight regime. Having the engine start running rough at the “slightest” leaning tells me it’s lean. He should be able to pull the knob a little more with Carb Heat ON though. With a fixed- pitch prop you should see a slight RPM increase while leaning. CSP you might notice a tiny airspeed increase.

If it was at high power the Economizer could be suspect. The Intake Couplings are protected by small shields to reduce heat deterioration. These often depart and the coupling gets fryed.

You can leak check the Induction System rather easily .

Disconnect the Carb Heat inlet duct.

Connect a CLEAN source of air ( pressure side of vacuum or leaf blower). It need not be high pressure or an airtight seal.

Carb Heat ON, Throttle open

pressurize and squirt with soap n water.
 
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Whitewaterraftr said:
No engine data other than fuel flow. Plugs, filter and mags look good. Fuel flow at 23" is only 13 full rich, that can't be right, can it?
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Different year etc ymmv - iirc more like 18 but I lean right away

I guess highest fuel flow I’ve ever seen is low 20s but at takeoff (26” or 27)
 
From the C182A POH:

upload_2023-3-27_16-23-31.png

A bit fuzzy, but readable. Those numbers are with the mixture leaned.

http://www.akmtnsoaring.com/wp-content/uploads/1957-Cessna-182-Owner_Manual.pdf

A long shot: O-470. An owner once complained that he had low power on takeoff. Aborted it. I found a chip of paint stuck in the secondary venturi of the carb. That's the venturi that the main nozzle is in, and that paint chip had restricted the secondary's airflow and thereby reduced the fuel flow. The cowl had been painted when the airplane was painted, but the painter had shot paint into the intake air tunnel in the cowl without either masking it off or prepping the surface for paint, and a chip of it had flaked off and been sucked into the carb. Thick flake, too. I had to disassemble the tunnel and strip it and prep and prime it properly.
 
Pressurized the induction system and didn't find any leaks. Didn't find anything in the carb either. Seems to come and go but gets fairly consistent at altitude.
 
Whitewaterraftr said:
Seems to come and go but gets fairly consistent at altitude.
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Did it run rough before the annual mentioned in post #6? Did you recheck the plugs (with pressure and the resistance) and wires (megohm) after it ran rough?
 
Ran fine before the annual. Just had the plug rechecked today and they also pressure and resistance tested the plugs. The mechanic said the idle mixture wasn't adjusted right but I'm not sure if that could be a problem or not.
 
None of the induction system was messed with at annual.
 
Did you check and see if you might have a clogged fuel injector? If one of the cylinders isnt firing it would run rough and not make full power either… just something to think about. Obviously easier to diagnose if you have an engine monitor.
 
O-470 is carbureted. Just flew to lake tahoe and now it's running rich enough that it's running rough. Pull the mixture out excessively and it runs great. I think that tells me it's the carb.
 
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Fuel flow should be in the high teens.
Check your fuel vents.
 
Wagondriver said:
Fuel flow should be in the high teens.
Check your fuel vents.
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That's a good idea.

Cessna's inspection sheets call for a vent check every 100 hours. I used to shove a foot-long length of 3/8" hose over the vent tube, clamp it if I had to, and blow into it and crimp it shut with a special pair of vise grips to trap that air in there. Then I'd go to the opposite wing and open the fuel cap, looking for the little puff of air that should be there. No puff means either leaking fuel caps (which can reduce the tank pressure and hold back the fuel) or a blocked vent crossover.

Seems to me that those old airplanes had a vent tube under each wing, tanks still interconnected.
 
I get a puff of air out of the tanks when i refuel after flying.
 
Whitewaterraftr said:
I get a puff of air out of the tanks when in refuel after flying.
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You shouldn't. That means that the tiny hole in the vent check valve flapper valve is plugged. Air is getting in and not out. That could get expensive.
 
What altitude is your home base airport? If you are at or near sea level (it's dependent on pressure altitude), fuel flow at wide open throttle should be > 20 GPH, probably more like 21-22. Mixture full rich, obviously. Your MP should be close to your baro setting typically 29", or a inch less depending on the type (and condition) of your air filter.

The fact that your tanks seems to be pressurized is a problem, but I'm not sure it is related to this issue. As others have mentioned, there is a pressure relief hole in the tank vent flapper valve that can get clogged. If you fill the tanks and park with the left wing low (or jack the right side a bit) you will see fuel drip from the vent line behind the left strut. No drip would mean a clogged relief hole. On a hot day, fuel expansion in the tank can damage the bladder/tank if hole is clogged. But a fuel flow issue would be indicative of negative pressure in the tank, not positive, so that's why I'm not so sure this is related.

C.
 
It may be an idea to disconnect the fuel line at the drain and drain into large containers. If the vent is blocked flow will diminish.

Metal cans and proper grounding a must!
 
O-470R - Around 1300 feet MSL, 50F outside air temp, full-rich mixture. wide open throttle, full RPMs MAX fuel flow recorded was 22.2 gallons per hour


Same flight full rich, 2100 feet msl climbing 2450 RPMs, 22.7", flowing 16.6 gallons
 
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Checked the fuel vent and the vent check valve in the tank and it was all good.

I don't have an engine monitor.
 
Blew air through the vent, flows fine. I can suck air back out of the tank but it's really slow. Ended up pulling the check valve out and it looks fine.
 
Flow test. #27 is easy.

The Finger Strainer in your carb uses a special gasket with locking fingers that is generally 1 use.

Because of that it may not be pulled regularly.

Trash could reduce flow.
 
Magman said:
Flow test. #27 is easy.

The Finger Strainer in your carb uses a special gasket with locking fingers that is generally 1 use.

Because of that it may not be pulled regularly.

Trash could reduce flow.
Click to expand...

That filter is clean.
 
Some of the older 470 s I’ve met had issues with valve guide wear. This would result in erratic seating and sealing of

the exhaust port. It may show good compression and another check after rotating the engine might show bad.

Removing the Rocker Cover will expose the components. If you rotate the engine to slightly unseat the valve you

can get creative with a screwdriver or bar to check for “ wobble”. Not particularly accurate but it will identify

“ bad”. This also provides a way to check valve lift that might point to cam problems too.
 
Thought I'd give an update. Neve figured out what it was. Pretty much went away on its own. Coincidentally I'm overhauling three cylinders.
 
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