Engine stutter when throttle is applied

[flyingchump]

So I’ve had my 66 M20E for all of a month now and I’ve been having a problem for the last 2 weeks.  When I’m at low rpm and add throttle (just a little or alot) the engine falls off (sputters and chokes) for a second then runs better once I get up to higher RPM.  I’ve repeated this “condition” at all mixtures.  Full rich and all the way back to full lean.  Leaning the mixture makes the problem worse.  It seems to make full power during take off and curse seems fine. 

 

Some info:

-IO-360 A1A, 950 SMOH. 300 since top overhaul. (to help oil consumption)

-At idle, the plane is fairly smooth but feels like it half-misses every 4-5 seconds.  I’m told that's not uncommon. 

-Fuel pressure is normal and centered in the green.  

-Oil pressure/oil temps all in the green.

-Electric fuel pump on/off makes no difference.

-Mag check during run up shows 30-50 prm drop for each mag.  

-in-flight mag checks were fine

-if I slowly pull the mixture all the way out I get a 30 RPM rise before shutdown.

-Left/right fuel tank makes no difference. 

-The battery is 8 years old and getting weak but still does its job.

-Left mag; 500 hours since it was overhauled P/N 10-163005-2 

-Right mag; 500 hours since new P/N BL600644-1 was installed

-EGT’s seem to be normal.  1200 to 1350 on average during cruise

-I have a small oil leak which I think is coming from the prop governor.  It makes a mess but RPM control is stable. It needs to be adjusted as it gets to 2750-2790 rpm.  I just take off with half a twist out and it’s stable at 2700.

And I’m sorry  but I don't have an engine monitor yet. Only EGT’s.  I’ll install a monitor during the next annual.  I’ve only had the plane a month!

I was being supervised by a mechanic today and we pulled all the spark plugs.  All tops were good, bottoms were ok but just a little wet.  We cleaned and gaped the plugs. Reinstalled and no improvement. Then we removed the injectors and soaked them in acetone for an hour.  Reinstalled with no improvement…  He recommends that we replace the left mag with a Surefly and overhaul the right mag to see if that helps.  The mags need to be done but I feel like he’s not confident.

 

I’ll be going back to the plane tomorrow.  What do you all suggest I check?

[Ross Taylor]

I can't help...yet. But one more question, to add to your very detailed and helpful data... what's your field elevation? And congrats, from another '66 E owner.

[MIm20c]

I’d iran both mags and overhaul the fuel distribution block spider if it hasn’t been touched in a while. When was the overhaul done?

[flyingchump]

8 minutes ago, Ross Taylor said:

I can't help...yet. But one more question, to add to your very detailed and helpful data... what's your field elevation? And congrats, from another '66 E owner.

Thank you.  

MGJ is 370 FT

The plane came from Minnesota.  Not sure exactly where but the field I purchased it from was 1234 ft.

Maybe the mixture was set to their elevation and I need more richer mixture due to -1000 ft?  

[flyingchump]

Just now, MIm20c said:

I’d iran both mags and overhaul the fuel distribution block spider if it hasn’t been touched in a while. When was the overhaul done?

The mechanic I worked with doesn't IRAN mags.  He just sends them for overhaul.  At that cost the Surefly looks pretty attractive. 

When was the last overhaul done on the spider?  no idea.  Didn't see that in the log books.

Edited June 19, 2020 by flyingchump

[kortopates]

So When I’m at low rpm and add throttle (just a little or alot) the engine falls off (sputters and chokes) for a second then runs better once I get up to higher RPM. 

 

 

Just responding to the complaint above - but I bet now that I’ve highlighted through the quote - I bet you readily now see the issue!

 

If not, go back to your initial complex training. ALL power increase are done from right to left: mixture rich , prop forward, only then throttle. While ALL power reductions are done from left to right. So in a nutshell, you’re lugging the engine and of course it’s not going to run smooth. I am sure there is nothing wrong with respect to that issue.

 

True, you can make small power changed directly with just MAP - but that doesn’t describe a small change.

 

On the Mags, the speciality shop that IRANs mine charges me $375 for the 5yr/500 hr IRAN including typical parts but sometimes it can be worse. I’ve heard as much as $500 though - anyway a datapoint for your consideration but a Surefly is probably a great idea.

 

Enjoy your new E!

 

 

Sent from my iPhone using Tapatalk

[carusoam]

when no engine data is available... sometimes people post a video...

The way engines work...

It takes... air, fuel, and spark...
 

They are most challenged when changes are made...

Changes like acceleration are most challenging...

This is when the fuel system has to predict what the engine is going to need....

If you had an O360... the carburetor’s accelerator pump would be suspect....

Since you have fuel injection...the injection system has a similar function...

Check the logs for when the FI system was cleaned, serviced or OH’d last?

Is there a tube that delivers MP to the FI to help it predict the fuel requirement?

Sounds like the engine may be getting starved for fuel during the acceleration...  

It may help to become familiar with all things related to the fuel injector system...  Learn what the fuel injection system uses to provide fuel during acceleration...

Now that you mentioned, the problem gets worse when the mixture is leaned.... you have two things pointing towards the fuel injection system needing some help...

 

PP thoughts only, not a mechanic...

Best regards,

-a-

[flyingchump]

3 minutes ago, kortopates said:

If not, go back to your initial complex training. ALL power increase are done from right to left: mixture rich , prop forward, only then throttle. While ALL power reductions are done from left to right. So in a nutshell, you’re lugging the engine and of course it’s not going to run smooth. I am sure there is nothing wrong with respect to that issue.

 

Thank you.  I'm not sure we are talking about the same thing.  This issue is mostly a ground problem.  Prop and mixture are full forward for start up.  If i try to throttle up a bit to taxi the engine spits and sputters.  Maybe its too rich, I'd lean for taxi and the problem gets worse. 

I don't know how I'm lugging the engine the engine for taxing.  Please correct me if I misunderstood your comment.

[kortopates]

Thank you.  I'm not sure we are talking about the same thing.  This issue is mostly a ground problem.  Prop and mixture are full forward for start up.  If i try to throttle up a bit to taxi the engine spits and sputters.  Maybe its too rich, I'd lean for taxi and the problem gets worse. 
I don't know how I'm lugging the engine the engine for taxing.  Please correct me if I misunderstood your comment.

No, you’re right - I assumed you were in the air with low RPM and advancing throttle without first advancing mixture and prop.

With low RPM on the ground and advancing throttle caused stumbling describes a mixture issue with the idle mixture adjustment. Check your idle mixture by reducing rpm to min idle speed of 700 Rpm while full rich - then slowly lean to idle cut off. You should see a RPM rise of 20 to 50 rpm. Any less it's too lean, while any more it's too rich. If it's too rich, you can get some relief by aggressive leaning but nothing you can do if too lean except till your A&P adjust the RSA idle mixture adjustment.
Good luck, but I bet that's what it is!


Sent from my iPhone using Tapatalk

[Ross Taylor]

1 hour ago, flyingchump said:

Thank you.  

MGJ is 370 FT

The plane came from Minnesota.  Not sure exactly where but the field I purchased it from was 1234 ft.

Maybe the mixture was set to their elevation and I need more richer mixture due to -1000 ft?  

Ah, sorry...on my phone your location didn't show up.  In theory, changing elevation like in your case shouldn't require any adjustments since you set the mixture...I think...not an A&P, of course.  I know with our old carbed cars that was an issue, but with a mixture knob in the plane I don't think that's the case.  But I was wondering if you were up in the mountains somewhere.  But at 370'...never mind.    So, I'll be following along to learn something too.

EDIT, after reading @kortopates help above - am I right that there's no overall mixture adjustment required for differing homebase elevations (because we control the mixture)?  And, does the idle mixture get adjusted based on the home field?  And if so, is there any compensation in that circuit for flights to other fields...or will the idle at other elevations be off?  Asking because we're at 7000' but fly to CA and other lower elevations.

[RLCarter]

Is this a new problem or one you have always had?  If leaning makes it worse you might have an intake runner that is leaking (air leak)

[Ragsf15e]

3 hours ago, flyingchump said:

Thank you.  I'm not sure we are talking about the same thing.  This issue is mostly a ground problem.  Prop and mixture are full forward for start up.  If i try to throttle up a bit to taxi the engine spits and sputters.  Maybe its too rich, I'd lean for taxi and the problem gets worse. 

I don't know how I'm lugging the engine the engine for taxing.  Please correct me if I misunderstood your comment.

This probably doesn’t help your specific problem, but I’ll still say it...

There are as many start techniques as MS members, but I believe your poh says to start with the mixture lean.  Practices vary, and some people start with the mixture in various positions (i use about 1/3 Pulled out).

Once you get it started, the very next thing is to lean it until just barely idles smooth.  This is pretty well established.  If you open the throttle slowly in this condition, it should stumble and not accelerate.  You will have to add mixture to taxi. You can do your runup at full rich (although some people will do this relatively lean too).  Every time you stop lean it back out.  After landing, same thing, lean it aggressively.

If you’re pretty anal about this, you can make it through a whole year without fouling a plug or finding lead deposits at annual or having “slightly wet plugs”.

So if I added power to taxi on my engine it will stumble too... and that would remind me to richen it slightly to taxi.  If I tried to takeoff like this it will stumble and/or die totally.

[the_elkhartian]

Short story....I work at a at a very big flight school. We have a fleet of 70 single engine pistons, oldest being a 2013 model. Carbureted O-360s. I’m not at liberty to share the manufacturer’s name. But it rhymes with “Diaper”...

We fly a lot. Often >400 hours per day. 7 days a week. Last summer we had a rash of engine fires at startup. 6 planes melted down on the ramp, no injuries but half of them totaled the aircraft. It was always on startup. 

Diaper engineers were called in. Lycoming and carb manufacturer. NTSB. FAA. All of them said it was the pilots fault. Flooding the engines. Pilot error. Dumb pilots. 

So we bought a FLIR camera and boroscope. We tested and tested...until...we figured out that after shutdown, with no fuel flow and no airflow the engine and component temperatures actually RISE after shutdown for about the first 40 minutes. The heat soaks throughout the cowling and vaporizes the fuel in fuel lines running from electric fuel pump on the firewall to the carburetor. You open the mixture valve and vaporized fuel “steam” rushes into the carburetor and flushes all of the fuel in the bowl down down down into the air box. Get a backfire and whoosh you have an engine fire. 

That story isn’t directly relevant to this discussion, but this is. Diaper and Lycoming said that the only thing they knew to do was fly less. Or convert our fleet to fuel injection. So, they’re converting our whole fleet to fuel injection (mostly at their expense). 
 
But now we have fuel injected IO-360s dying in the run up area. “Stupid student pilots” they said. “Don’t try that again,” we said. 

So indeed, after discussing internally, the manufacturers decided that at idle during taxi there is insufficient airflow and fuel flow for fuel system components stay below 155 degrees (temperature at which fuel boils at our elevation). So, Diaper and Lycoming say not to retard the throttles below 1000 rpm while on the ground...keep fuel flowing, and it can’t vaporize. (This is while they work on approval for a fuel return circuit that flows fuel back to the reservoir at low rpm like in a Cessna.)

So your problem sounds like basically every day that I taxi a brand new and very well maintained airplane with an IO-360. Of course I’m in the desert at 1400’ with very hot engines. But like you, it clears right up as soon as you’re rolling down the runway. 

Not sure if that’s helpful. Also sorry that ended up being a pretty long story!

[Guest]

As Robert mentions above, an induction tube leak is a good possibility.  It sounds like a mixture issue.  Pull the side cowls and look for blue fuel staining around the induction flanges at the cylinder head or a dislodged O ring where the tube enters the oil sump.

Clarence

[HRM]

12 hours ago, flyingchump said:

When I’m at low rpm and add throttle (just a little or alot) the engine falls off (sputters and chokes) for a second then runs better once I get up to higher RPM.

My money, or should I say yours, is on the fuel servo. Induction leak an easier, less expensive first check as others pointed out.

[flyingchump]

9 hours ago, RLCarter said:

Is this a new problem or one you have always had?  If leaning makes it worse you might have an intake runner that is leaking (air leak)

Well, I've only had the problem for a month...  So this could have existed without me noticing for a bit but I dont think so.  I think I started using the plane more than it was being used so I probably "exposed" a problem that was going to rear its head anyway.  

I was thinking the same thing about an intake leak.  I'm going to order some new intake gasket seals and intake tube orings.  I'll take the intake apart to get a closer look and replace seals as i go. 

[flyingchump]

1 hour ago, HRM said:

My money, or should I say yours, is on the fuel servo. Induction leak an easier, less expensive first check as others pointed out.

I'm on the road of checking the easy stuff already.  I'll check all the intake and fuel systems from the engine backwards to see if I can find something...  but it all leads back to the fuel servo.

Any idea if fuel servos can be serviced locally or do they need to be sent out for overhaul?

[HRM]

1 hour ago, flyingchump said:

Any idea if fuel servos can be serviced locally or do they need to be sent out for overhaul?

Mine had to be sent out. The difference after it was rebuilt was noticeable.

[flyingchump]

2 hours ago, HRM said:

Mine had to be sent out. The difference after it was rebuilt was noticeable.

Where did you send it?  Got a website you could share?

[MB65E]

What is your idleing Rpm set to? compare with the TCDS. 

The Idle mixture rise should be checked at 900 rpm. 

Check the injectors for debris, but they are probably fine. As they don’t do much at idle. 

Is the sniffle valve leaking or working properly? 

If you still have issues. Pull the spider and fuel servo. Send to RLB accessory service in Addison IL. I’ve worked with them for 17years. Great shop.

-Matt
 

[jlunseth]

An idle rise is normal, probably you know that. As Paul said, it should be 20-50 RPMs and I have seen statements that 75 is normal, although in practice I tend to see around 50-60 in my aircraft (a 231). That is one of the first things you should do after start-up, lean the mixture to max idle rise and then taxi at that setting.  Possible you are too rich if you are idling with the mixture full in. My engine is definitely different from yours (turbocharged - they are intentionally set up very rich), I need to keep it leaned out on final or on the ground or I get a “burble.” Hard to explain the difference, but a burble is different from a miss.  A miss is sharp, a burble is a miss but it is not sharp.

If your mags are at 500, OH them you are running on borrowed time. If you don’t do it at your convenience, then a mag will go down when you are away from your home field and it will make you do the OH at its convenience, not yours. If you are lucky there will be an AP there and if you are really lucky he will have a replacement mag, but if not you get to find your way home and wait while the mag shows up, then find your way back to fly the plane home.

[HRM]

4 hours ago, flyingchump said:

Where did you send it?  Got a website you could share?

My A&P sent it somewhere in Houston. I have the receipt somewhere, but your mechanic should have one in mind. I don't think there are that many shops that do it anyway. They take it apart, clean it, replace seals and worn parts and then test it. Given the number of IO-360s, there should be a good shop known to your A&P.

[flyingchump]

10 hours ago, M20Doc said:

As Robert mentions above, an induction tube leak is a good possibility.  It sounds like a mixture issue.  Pull the side cowls and look for blue fuel staining around the induction flanges at the cylinder head or a dislodged O ring where the tube enters the oil sump.

Clarence

No blue fuel staining around the intake.  If I was sucking in air through a flange would I even see blue staining?  I'm going to replace the gaskets and orings anyway. They are like a buck each and easy to change so why not.  Maybe I'll see something else while i have it apart.

[Guest]

2 hours ago, flyingchump said:

No blue fuel staining around the intake.  If I was sucking in air through a flange would I even see blue staining?  I'm going to replace the gaskets and orings anyway. They are like a buck each and easy to change so why not.  Maybe I'll see something else while i have it apart.

You would think that with the intake system being under vacuum that there would be no external staining, but it does leak out as well.  
With the pipes removed use a straight edge to make sure that the flange of the tube is slight proud above the aluminum flange.
Be sure to use new lock washers and torque the 1/4-20 bolts to 96-100 inch pounds with the tube flange centered in the aluminum flange.

Clarence 

[RLCarter]

4 hours ago, flyingchump said:

No blue fuel staining around the intake.  If I was sucking in air through a flange would I even see blue staining?  I'm going to replace the gaskets and orings anyway. They are like a buck each and easy to change so why not.  Maybe I'll see something else while i have it apart.

When I purchased my E I pulled the intake tubes off to clean them up a repainting, one of the O-rings was was missing a fairly big chunk, no way it was sealing and there was no signs of fuel stains. Can’t remember if there was a running issue as I only ran it long enough to run a differential compression test