Rough Engine M20C

[Boilermonkey]

My partner called and said he diverted due to a rough engine. He was in cruise just bellow a scattered layer so carb heat was the first thought. He applied carb heat for 5 minutes and it went away. He turned off carb heat and the roughness reutrned with a minute. He switched tanks, checked fuel pressure, and oil...all ok. He said the when leaning there wasn't a clear peak so the egt was only in the 1200s.

 

I should mention that we have had issues starting in the cold and occasionally get an engine hiccup when advancing the throttle quickly. We suspect the carb accelerator may need to be looked at...but I don't suspect that would be the issue here at cruise.

 

He diverted and landed safely. He did a run up and it purred like a kitten...all OK. We're going to have a mechanic do a check... however we are looking for feedback.

 

So, was it just carb ice? Ive had similar symptoms in a C172 and needed to leave carb heat on until out of the cloud layer. Thoughts?

 

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[steingar]

Could have been. You can get carb ice in the absence of visible moisture.

[smwash02]

One of my worst rough running carb ice incidents was on a trip from Austin to HFY, actually, passing over Dyersburg, TN around this time of year. Not a cloud in the sky, but boy was it muggy on the ground.

Being relatively green still, I used carb heat and made a precautionary landing. Plane was fine after that. I also added mixture, which is the opposite of what should be done with carb heat on.

Given the troubles you've had, it's probably time for the 500 hour mag check if it's not been done and a carb exchange/overhaul. You'll also want your flapper and diverter checked that they're sealing well.

[carusoam]

Just below the clouds is a high RH area that turns into visible moisture as it rises... great place for carb ice...

Got a carb temp...yet?

 

Acceleration issues + lots of pumps needed for really cold starts.... expect your accerator pump wants attention...

 

Find a good carb guy that knows these things...

 

Running full carb heat, full throttle, at max gross... you wish you had a carb temp indicator to safely get more HP by running less carb heat...

PP thoughts only, stuff my M20C taught me...

Best regards,

-a-

[Hank]

Carb temp gages are wonderful things. I've applied partial carb heat in the clouds when the carb temp needle was in the orange stripe, just have to lean the engine again.

[Boilermonkey]

Update. The plane flew fine today. Must have been carb ice. Still thinking about a carb OH at annual since we have cold start problems.

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