Engine Roughness on taxi in

[butchgilbert]

Was out sick for month, finally went flying today, and on taxi in the engine seemed to run rough and vibration on the ground during taxi seemed rougher than normal. JPI was absolutely normal entire flight.  Rpm above 1200 seemed normal as well, run up normal. M20F, IO360 A1A 1975 Mooney Executive.

Any thoughts?  Was thinking it could be a stuck valve??

 

[aerobat95]

Is it possible that you have some plug fouling?

[Piloto]

Sounds like an idle over rich mixture setting. Try this: on idle pull the mixture slowly until the engine smooth out. If you can get the engine to run smooth then your idle mixture setting needs to be adjusted. I would also check the side hex plug on the servo for looseness. Recommend you do this before next flight. You may have a loose mixture linkage on the servo. Also check the mag timing, it should be 25deg BTDC. More than 25 would cause also idle roughness.

 

José

[danb35]

Mag timing should probably be 20 BTDC, not 25.  Check the engine data plate to be sure.

[Shadrach]

Quote: danb35

Mag timing should probably be 20 BTDC, not 25.  Check the engine data plate to be sure.

[sreid]

Induction leak?

[tony]

http://www.sacskyranch.com/eng38.htm

http://www.dgsupply.com/trouble.html

check the trouble shooting chart.

 

[Shadrach]

Quote: sreid

Induction leak?

[Shadrach]

Duplicentur Nuntium...

 

[John Pleisse]

Quote: Shadrach

The likely culprit...

 

[N6936V]

Had same symptoms; turned out to be a stuck mixture cable.  Had to be replaced for $400. 

Good Luck!

[butchgilbert]

Thanks everyone for your advice, I will check with my FBO MX guys to take a look at the engine, an induction leak sounds plausible.

However, I am definitely going to have the mag timing checked (I think 25 degrees BTDC is correct), the mags are virtually brand new last summer.

I do get about 100 RPM drop on one side and about 50 on the other side, have not noticed any problems, and like I said the JPI shows every

cylinder running about where I would expect them to.

I also thought it could be a prop imbalance, but I had no problems after the November 2011 annual, just after being stuck on the ground for about a month.

 

Thanks again for your suggestions.

 

Butch

[jetdriven]

100 RPM drop on mag check is too much.  Ross got it right, the 20 degree timing is an optional band aid fix. We set ours to 25 degrees and we are talking maybe 10-20 HP more here.  Check the 'sniffle valve" as Don Maxwell points out here http://www.donmaxwell.com/publications/MAPA_TEXT/External_Hoses/External_Hoses_Tubes.htm       It caues rough running and loping at idle.

[butchgilbert]

Flew today, on initial run-up, #2 lower cyl spark was fouled pretty bad.  Was able to clear it and fly, but it sure seems that the spark plug (new last year) is the real source of the trouble.  Inflight very smooth and all EGT's were within 30-40 degrees. 

Goes to show you that you really need to fly these airplanes as often as possible. In my almost 13 years of owning this airplane, I can't remember not flying for as long a period of time as just recently due to a back injury.

Thanks again for all your inputs.

[jetdriven]

Check the ohms of the center electrode. Champion plugs, in a word, suck.  They have very high resistance sometimes and their fine wire plugs crack.

[butchgilbert]

Will do, what spark plug manufacturer and type (have always used Champion massives) would you recommend?

I have never gotten very long service out of Champion plugs.

[jetdriven]

Below 5,000 ohms resistance.  

 

[butchgilbert]

One last post: After cleaning and running up 6902V today with newly cleaned #2 cylinder spark plugs, during run up set rpm at 700 RPM and pulled mixture lever toward cutoff, RPM increased from 150-200 RPM, seems like a very rich idle mixture setting. Having it adjusted tomorrow.

After shutdow, took the following pictures, you can see some plastic (probably a seal) protruding out from under the spinner in front of the prop blade. NOT HAPPY!!

More later. Again, thanks for all the assistance

[butchgilbert]

Final analysis, spinner support successfully replaced, and adjusted idle mixture setting.  I now have a super smooth running engine.