Temporary Rough Engine At Cruise

[Hawth200]

Hank,

 

Thank you for the invitation! I'll keep that in mind. Too bad your moving.

 

 

M204ER,

 

You are correct. MP will always drop when carb heat is applied... When the question was raised, I just assumed that they were asking if I had noticed a drop in MP before carb heat was applied, indicating a possible carb ice situation.

[philiplane]

Yesterday, while cruising at 6500', my carbureted O-360 started running very rough (like I had lost one cylinder) and I noticed that the single cylinder EGT indicator was indicating about 100 degrees higher than normal. The CHT was indicating normal. I figured that the mixture setting had become overly lean, so I began to enrichen the mixture.

 

The change in mixture made no difference in the rough running engine and strangely the EGT indicator did not react to the change in mixture. The fuel pressure was normal. I did not switch either magneto off, but decided to next apply carb heat to see what effect that would make. With carb heat applied, the engine began to stumble even worse and did not clear up. From that, I figured that I now must be running an overly rich mixture setting.

 

I began to lean the mixture back out ignoring the EGT indicator that was still reading about 100 degrees high. As I leaned the mixture the engine began to run smoothly again. I kept my eye on the EGT indicator. It continued to read 100 degrees high for a few minutes before settling back to normal. The engine operated normally for the rest of the flight (about 40 mins). While it felt like an eternity, the roughness probably didn't last more than 3 or 4 minutes.

 

I'm just trying to come up with a reasonable explanation for this. My first thought was that I may have experienced a sticky exhaust valve...  

 

I just thought I would mention it here to see if anyone had any possible explanations.

 

 

Thanks!

 

 

Seth

 

 

Yesterday, while cruising at 6500', my carbureted O-360 started running very rough (like I had lost one cylinder) and I noticed that the single cylinder EGT indicator was indicating about 100 degrees higher than normal. The CHT was indicating normal. I figured that the mixture setting had become overly lean, so I began to enrichen the mixture.

 

The change in mixture made no difference in the rough running engine and strangely the EGT indicator did not react to the change in mixture. The fuel pressure was normal. I did not switch either magneto off, but decided to next apply carb heat to see what effect that would make. With carb heat applied, the engine began to stumble even worse and did not clear up. From that, I figured that I now must be running an overly rich mixture setting.

 

I began to lean the mixture back out ignoring the EGT indicator that was still reading about 100 degrees high. As I leaned the mixture the engine began to run smoothly again. I kept my eye on the EGT indicator. It continued to read 100 degrees high for a few minutes before settling back to normal. The engine operated normally for the rest of the flight (about 40 mins). While it felt like an eternity, the roughness probably didn't last more than 3 or 4 minutes.

 

I'm just trying to come up with a reasonable explanation for this. My first thought was that I may have experienced a sticky exhaust valve...  

 

I just thought I would mention it here to see if anyone had any possible explanations.

 

 

Thanks!

 

 

Seth

Do you have Champion spark plugs, and/or Slick magnetos? 

 

If so, there is a possibility you have a developing ignition problem you don't want to ignore.

[Guest]

A fowled plug on cylinder three would cause the problem you describe. When one plug stops firing the EGT will rise. When you leaned it out the plug started firing again. When you did your ground run up it was working ok, you said it smoothed back out. Next time check your mags in flight. It is the first thing you should do. If it runs smooth on one mag then run on that mag and periodically check the other side by going to both to see if it has cleared itself. It doesn't do your engine any good to run on both when L or R is smoother.

I have talked to other mechanics who are amazed that pilots will fly for hours on both instead of turning off the bad mag. That is what the key is for....

Sorry I can't resist, if the plug is fowled, did he have a bird strike? If so at what EGT should it be cooked?

Clarence

[PTK]

Clarence, I would cook it by reference to CHT. EGT will scorch it rendering it in indigestible!

[N201MKTurbo]

We learned it in A&P school. When a bird $&/?s on your spark plugs they quit working....

[Guest]

Good point!

Clarence