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IO-520 Low Idle and Stumbles

behindpropellers

behindpropellers

Registered User
NE Ohio
Chasing this right now:

IO-520A Rebuilt Mags and New Engine controls.

1. Idle is low.
2. When advancing throttle it stumbles before catching up.


Informed guess: Previous throttle cable was adjusted to give the correct idle RPM. Fuel flow is not up to spec on the low end.

Gauges go on the fuel system next week...

Tim
 
yes step one, get fuel high & low pressure correct, to high end of range on high.(well at least for sea level)

get it to idle as low as it will stay running, if you got a good cam this can be down to ~350, you should see a little black smoke out of exhaust when mixture is correct at this low idle, not that you idle it that low always, but helps for landing..
 
Just just went through this on my 520. Sounds like your idle mixture is to lean. Do you get a small rise as you cut the mixer? If not, to lean. This will cause a stumble when advancing throttle from idle..
check your high and low fuel pressure, adjust idle and idle mixture. Then you should b good..


behindpropellers said:
Chasing this right now:

IO-520A Rebuilt Mags and New Engine controls.

1. Idle is low.
2. When advancing throttle it stumbles before catching up.


Informed guess: Previous throttle cable was adjusted to give the correct idle RPM. Fuel flow is not up to spec on the low end.

Gauges go on the fuel system next week...

Tim
Click to expand...
 
If I remember correctly, the manual I have says set the rpm at 1000. Slowly pull the mixture out to almost cutoff. As you lean, the rpm shud increase about 50 rpm, then decrease. This shud give you a quick idea of how to adjust the mixture.
 
Clean the injectors, I use Hoppies #9 in an ultrasonic hot pot. Mine really hesitates and won’t come off idle unless you baby it if the injectors have more than say 250-300hrs since the last cleaning. Also if you are getting a little fuel drip out of the injection vent line after shut down the flow divider may need a rebuild, just had that done.
 
Last edited:
charlesf said:
If I remember correctly, the manual I have says set the rpm at 1000. Slowly pull the mixture out to almost cutoff. As you lean, the rpm shud increase about 50 rpm, then decrease. This shud give you a quick idea of how to adjust the mixture.
Click to expand...
This is standard procedure for ALL engines for determining idle mixture setting, not just the big Continentals.
 
OLDCROWE said:
Clean the injectors, I use Hoppies #9 in an ultrasonic hot pot. Mine really hesitates and won’t come off idle unless you baby it if the injectors have more than say 250-300hrs since the last cleaning. Also if you are getting a little fuel drip out of the injection vent line after shut down the flow divider may need a rebuild, just had that done.
Click to expand...

Had an IO-520 in a C210 that I had to clean the injectors every 100 hours or it would hesitate like that.
 
That’s more junk on the screen than I’ve seen in 5+years combined on mine. I’m with Steve, what’s coming apart or got in the system, as I understand the system that’s the last chance screen.

How long has it been since the last cleaning?
 
OLDCROWE said:
That’s more junk on the screen than I’ve seen in 5+years combined on mine. I’m with Steve, what’s coming apart or got in the system, as I understand the system that’s the last chance screen.

How long has it been since the last cleaning?
Click to expand...

I'm going to call the last guy who did the annual and ask him about it. There actually is one more screen, in the fuel divider.

Any favorite continental fuel injection shops you guys recommend?
 
from the Rolodex: ;)
Mike's Fuel Metering
9406 East 46th Street North
Tulsa, OK 74117
918-838-6217

Been a while since I did anything fuel injected but he was good to me.
 
since that filter is after gascolator & screen, I would say, start with the gascolator to determine the screen in it is not damaged, to have let all that by.... never seen that much downstream...
 
I had the carb inlet screen (aka last chance filter) clog once in my old C170 ragwing.
This was downstream of both the screen in the gascolator and the screen in the engine-driven fuel pump.
Itty bitty red fibrous debris, looked like someone dropped a red shop rag in the fuel tank and it slowly dissolved.
 
hotrod180 said:
I had the carb inlet screen (aka last chance filter) clog once in my old C170 ragwing.
This was downstream of both the screen in the gascolator and the screen in the engine-driven fuel pump.
Itty bitty red fibrous debris, looked like someone dropped a red shop rag in the fuel tank and it slowly dissolved.
Click to expand...

Drained the tanks and I am starting there....should be interesting.

Tim
 
Pulled the gascolator last evening, not much in it as far as debris. Right header was clean. Left header had some water and gunk in it.

Tim
 
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