1966 M20e IO360 AIA sometimes stumble on run up runup

[Cabo Lee]

Okay, I need some advice. The 1966 M20e sometimes stumbles on runup. The problem acts like dirty plugs. What been done: replace plugs with fine wire, both Magnetos have recent re build with new P leads,recently new spark plug wires  and clean fuel injector nozzels cleaned and checked.The plane will fly perfect for several hours in the air. However at runner the problem can reappear. Help, any suggestions??

[Yetti]

Check valves, when was the fuel servo rebuilt last.  Check all filters.  Finger Screen, One by Elect fuel pump.

[chriscalandro]

It might just be you aren’t leaning enough on the ground. 

[FlyingCanuck]

I had a similar issue on my F, same engine. There were two causes:

1. Mixture was set too rich. I had to lean it almost all the way back. That said, the problem was mostly at lower RPMs, i.e. 900-1100. 

2. First flight of the day, it would start-up rough and run rough for a few minutes. Well documented problem nick-named 'morning sickness.' It was a sticking exhaust valve. Had to have the valve reamed (and push rod replaced).

Have you looked at the Lycoming trouble-shooting docs? There's a few good ones online that give you a punchlist of potential items. In my case, it was spot on.

[67 m20F chump]

I was thinking too lean at low rpm.  I would check intake to see one is hanging down a bit.

[RobertGary1]

When taxing out for runup make sure that adding throttle doesn’t cause much increase in rpm. The mixture at taxi should be lean enough that you must enriched to increases power. 

[carusoam]

+1 for leaning a lot while on the ground...

Lead build up on the plugs will do this...

This light coating occurs after start-up and a short taxi... and often results in tiny lead beads residing in the lower spark plugs...

Add a few lines to the Start up and T/O procedures...

Full throttle and deep lean should give a big reminder stumble if you fail to follow your new checklist...

PP thoughts only, not a CFI...

Best regards,

-a-

[Nukemzzz]

On 12/14/2020 at 10:59 AM, chriscalandro said:

It might just be you aren’t leaning enough on the ground. 

How much do you guys lean during taxi?  Back when my plane was still running I had two cases of fowled plugs on run-up and had to lean way out and run up to burn off fowling.  It's not clear to me how to tell when the lean is good for taxi.

[EricJ]

30 minutes ago, Nukemzzz said:

How much do you guys lean during taxi?  Back when my plane was still running I had two cases of fowled plugs on run-up and had to lean way out and run up to burn off fowling.  It's not clear to me how to tell when the lean is good for taxi.

Almost to idle cutoff, as long as it runs reasonably smoothly.   You only need it rich enough to run smoothly for taxi, and keep the engine at 1000 rpm or a little above.

Running it extremely lean on the ground at very low power doesn't hurt anything, and keeping it *way* lean on the ground means that you can't inadvertently take off with it too lean as it won't run well at all as the throttle is advanced.

Edited December 17, 2020 by EricJ

[Guest]

3 hours ago, Nukemzzz said:

How much do you guys lean during taxi?  Back when my plane was still running I had two cases of fowled plugs on run-up and had to lean way out and run up to burn off fowling.  It's not clear to me how to tell when the lean is good for taxi.

How did these fowl enter your engine?  Do you have to report this as a bird strike?

Clarence

[RobertGary1]

On 12/17/2020 at 1:17 PM, Nukemzzz said:

How much do you guys lean during taxi?  Back when my plane was still running I had two cases of fowled plugs on run-up and had to lean way out and run up to burn off fowling.  It's not clear to me how to tell when the lean is good for taxi.

Add full throttle. If the rpms increase more than a couple hundred it’s too rich. 

[Pilot boy]

On 12/14/2020 at 4:43 AM, Cabo Lee said:

Okay, I need some advice. The 1966 M20e sometimes stumbles on runup. The problem acts like dirty plugs. What been done: replace plugs with fine wire, both Magnetos have recent re build with new P leads,recently new spark plug wires  and clean fuel injector nozzels cleaned and checked.The plane will fly perfect for several hours in the air. However at runner the problem can reappear. Help, any suggestions??

I have an E model.  I always lean as soon as I start up and especially for the taxiing.  I lean always except when in the pattern doing touch n goes.  I found that the mags would try to drop just a hair too far but the buildup clears as soon as you run up to 2100 rpm for a minute and burn it off.  Be sure to lean, especially before shutdown or it will be a beast to restart.

[Pilot boy]

On 12/17/2020 at 3:17 PM, Nukemzzz said:

How much do you guys lean during taxi?  Back when my plane was still running I had two cases of fowled plugs on run-up and had to lean way out and run up to burn off fowling.  It's not clear to me how to tell when the lean is good for taxi.

I lean it quite far out for taxi even in winter, probably at least halfway or a little greater...my guess is about 5/8 out.  I watch my EGTs on hot days and just try to keep it not too hot (like 1400 EGts] This pretty much eliminates any run up issues with the mags when I enrichen it right before run up.  I then lean it again until I’m about to enter the runway. MAKE SURE NOT TO FORGET TO GO RICH FOR TAKEOFF.  

[Hank]

On 12/17/2020 at 3:17 PM, Nukemzzz said:

How much do you guys lean during taxi?  Back when my plane was still running I had two cases of fowled plugs on run-up and had to lean way out and run up to burn off fowling.  It's not clear to me how to tell when the lean is good for taxi.

Probably 2/3 towards Cut Off. When I have to add power to taxi uphill, the engine will stumble. A recent flight ended parked in grass, and when I added throttle to pull onto pavement, the engine almost died before I remembered to richen up. Takeoff with a properly leaned engine is impossible, but if you don't lean enough you can have a long takeoff run with reduced power and elevated cylinder temperatures.

[PT20J]

On 12/14/2020 at 2:43 AM, Cabo Lee said:

Okay, I need some advice. The 1966 M20e sometimes stumbles on runup. The problem acts like dirty plugs. What been done: replace plugs with fine wire, both Magnetos have recent re build with new P leads,recently new spark plug wires  and clean fuel injector nozzels cleaned and checked.The plane will fly perfect for several hours in the air. However at runner the problem can reappear. Help, any suggestions??

Is it on one mag or both? Does the plug burnout procedure clear it? 

[RobertGary1]

3 hours ago, Pilot boy said:

I lean it quite far out for taxi even in winter, probably at least halfway or a little greater...my guess is about 5/8 out.  I watch my EGTs on hot days and just try to keep it not too hot (like 1400 EGts] This pretty much eliminates any run up issues with the mags when I enrichen it right before run up.  I then lean it again until I’m about to enter the runway. MAKE SURE NOT TO FORGET TO GO RICH FOR TAKEOFF.  

Shouldn’t have to worry about take off. If you’ve leaned correctly you won’t get much rpm increase at full throttle so it will be obvious. 

[Hank]

1 minute ago, RobertGary1 said:

Shouldn’t have to worry about take off. If you’ve leaned correctly you won’t get much rpm increase at full throttle so it will be obvious. 

I lean enough so that half-throttle will choke it down. Full throttle would probably kill the engine, drowning it in fuel that can't burn due to lack of air.

[Pilot boy]

On 12/20/2020 at 8:38 PM, RobertGary1 said:

Shouldn’t have to worry about take off. If you’ve leaned correctly you won’t get much rpm increase at full throttle so it will be obvious. 

That’s true I just don’t want him to lean some but not enough and just lack power for takeoff and not realize what it is.  The middle ground is dangerous with the mixture where you have enough for nearly full power but not quite enough.  Just trying to give a word of caution 

[Hank]

2 minutes ago, Pilot boy said:

That’s true I just don’t want him to lean some but not enough and just lack power for takeoff and not realize what it is.  The middle ground is dangerous with the mixture where you have enough for nearly full power but not quite enough.  Just trying to give a word of caution 

 

On 12/20/2020 at 8:43 PM, Hank said:

I lean enough so that half-throttle will choke it down. Full throttle would probably kill the engine, drowning it in fuel that can't burn due to lack of air.

If your engine ain't bucking like a bronco at half throttle, you aren't properly leaned for ground operations . . . .