Engine running rough

[Mooneyjet]

Beautiful evening tonight so I took the mooneyjet for a flight, on top of the climb I selected the carb heat full on and the engine started to run rough, my first instinct was to shut the carb heat off I level the mooney and did a cause check, I tried mags, and it all check out. I then turn the carb heat back on and once againg the engine started to run. Very rough to the point that I was starting to look for a field to land, I reduced the power and tried the. Carb heat and voila it run smooth like it always has when carb heat is applied, I applied power to 25 square. And again the engine would run rough with the carb heat on. Has anyone experience anything similar to my snag.  The irony is that one of my last post was about converting a carb to fuel injection go figure looks like the old girl is barking  back. 

[Lood]

At what altitude were you flying and what was the mixture setting?

[1964-M20E]

Well I have the fuel injected IO-360 and have not flown behind a carbureted engine for a while.

1. 
   
2. Why do you want to put the carburetor heat on at 25 squared?
   
3. I was taught to use carburetor heat during the approach to landing phase of flight and if you noticed the engine was running odd during level flight in conditions that might produce carburetor ice.
   
4. Carburetor heat should not be needed during the climb or during normal cruise flight.
   
5. Carburetor heat passes warmed air into the engine decreasing power due the warmer air having a lower density than the cooler air.
   

[jetdriven]

THe biggest thing is the les dense warm air ingested by the carburetor makes it run richer. If it is already very rich, it can run rich enough to run rough.

[carusoam]

Back in the day with my M20C...

The control cable would bend and not operate properly, strangling the intake...

Check the operation of the system...  The airflow seems strangled even when operating properly.

Then buy a fuel injected model....

Best regards,

-a-

[BigTex]

A couple of thoughts... I've actually experienced engine roughness when climbing out and forgetting to lean out.  Did you attempt to do any leaning to see if that made any difference?

Also, I had an issue where my engine ran rough anytime I increased MP beyound 24".  That turned out to be a mag issue where the timing was off on the left mag.

[N9453V]

Why did you apply carb heat at the top of the climb? Did you notice an unexpected drop in manifold pressure? I can't think of any other reason to apply it in that phase of flight.

-Andrew

[DaV8or]

I've never flown a carburated Mooney, but I have lots of time in other brands with carbs and I'm wondering, why did turn the carb heat on? It sounds like you want to cruise with carb heat on and this puzzles me. To me, it sounds like your plane is working perfectly. Carb heat causes the engine to run richer and at altitude, it can make it too rich for proper combustion. Also, the carb heat is not an all or nothing proposition. It is variable. So if you apply it full in cruise and the engine complains, set it somewhere inbetween full and off. You should be able to find a setting that will allow you to cruise with the carb heat on. Again though, I'm not sure why you want to.

On the other hand, if you do have carb ice, when the carb heat starts to melt the ice, the engine will run really bad until it's all gone, then it should run smooth again.

[Oscar Avalle]

I agree, recently I was landing at an airport that was 5000 feet high, after doing my GUMPs check I enriched the mixture and because I was IMC I put on Carb Heat, and the engine started to run very rough. Inmediatly I leaned the mixture and the engine was fine again...

[jetdriven]

Checklist says "mixture-richen" not "mixture - full rich". 

[Oscar Avalle]

Byron, Indeed depending on the density altitude it does not need to be "full rich" to have a negative effect....

[Mooneyjet]

Thanks for the positive replies, I'm new to carb operations and I was not aware that with higher engine power it would have such effect of running that rough however it makes a lot of since. I do not intend to operate with the carb heat on . 

[rbridges]

Quote: Mooneyjet

Thanks for the positive replies, I'm new to carb operations and I was not aware that with higher engine power it would have such effect of running that rough however it makes a lot of since. I do not intend to operate with the carb heat on . 

[Seth]

Quote: rbridges

stick around.  there is a lot of good info on this board.  You'd be amazed at how knowledgeable some people are.

[Hank]

Quote: Mooneyjet

Beautiful evening tonight so I took the mooneyjet for a flight, on top of the climb I selected the carb heat full on and the engine started to run rough, my first instinct was to shut the carb heat off I level the mooney and did a cause check, I tried mags, and it all check out. I then turn the carb heat back on and once againg the engine started to run. Very rough to the point that I was starting to look for a field to land, I reduced the power and tried the. Carb heat and voila it run smooth like it always has when carb heat is applied, I applied power to 25 square. And again the engine would run rough with the carb heat on. Has anyone experience anything similar to my snag.  The irony is that one of my last post was about converting a carb to fuel injection go figure looks like the old girl is barking  back. 

[Hank]

double post--hit "Submit" and lost everything on the screen except the Mooneyspace.com header.

[Hank]

triple post--I hit "Refresh" twice, then closed Explorer.

[WardHolbrook]

Quote: DaV8or

I'm wondering, why did turn the carb heat on?

It sounds like you want to cruise with carb heat on and this puzzles me.

Carb heat causes the engine to run richer and at altitude, it can make it too rich for proper combustion.

Also, the carb heat is not an all or nothing proposition. It is variable. So if you apply it full in cruise and the engine complains, set it somewhere inbetween full and off. You should be able to find a setting that will allow you to cruise with the carb heat on. Again though, I'm not sure why you want to.

On the other hand, if you do have carb ice, when the carb heat starts to melt the ice, the engine will run really bad until it's all gone, then it should run smooth again.

[Hank]

Good point, Ward.

Partial carb heat works well if you have the "optional Carb Temp Gage" otherwise it should be all or nothing, as in the 172's I trained in. My Carb Temp Gage is an obvious aftermarket, marked in ºC where the OAT is in ºF. But it is functional, I've seen it move around. When it gets into the orange stripe, if the weather is hazy, below freezing and threatening, or in IMC I crack the carb heat until it moves out of the orange. So far, so good.

[WardHolbrook]

Quote: Hank

Good point, Ward.

Partial carb heat works well if you have the "optional Carb Temp Gage" otherwise it should be all or nothing, as in the 172's I trained in. My Carb Temp Gage is an obvious aftermarket, marked in ºC where the OAT is in ºF. But it is functional, I've seen it move around. When it gets into the orange stripe, if the weather is hazy, below freezing and threatening, or in IMC I crack the carb heat until it moves out of the orange. So far, so good.

[thinwing]

Once on a water takeoff from a remote canadian lake I left the carb heat on from the previous landing.Applying full throttle,full rich for the takeoff reduced manifold pressure enough (almost 2 inches)that the Husky I was flying not only wouldnt takeoffbut wouldnt even get up on the step.I thought I would end up spending the night at this remote ,high altitude lake untill I saw the carb heat knob pulled all the way out...it has that much effect..kpc