Rough engine on take off

[Angie]

This happened to me and the plane owner after a 100 hour maintenance that he had just completed.
I was flying the 152, and he was in 2nd seat relaxing until about 200 ft AGL. The engine started running really rough. He started checking the controls to get it to run smoother. It would not run smooth, so he took over flying in it a low pattern and landing it.

I later found out that we could have killed ourself due to the engine running so roughly.

The cause, a carter key was not in good on the fuel feed.

Has anything like that happened to you?

 

[Magman]

Elaborate on Cotter Key?

 

[Angie]

https://www.grainger.com/product/2U...cga0XdZ_Uc6O-z-avBRoCX3cQAvD_BwE&gclsrc=aw.ds

It was used in the fuel delivery system at some point to hold something in place correctly.

 

[sierrakilo99]

Only place I've seen those 'pins' is the ones that are holding the battery box lid onto the bottom half of the box.

sk

 

[Angie]

I don't know where it was, as I received the information about the rough engine apparently not getting a good fuel supply about 2 weeks after it happened.
The owner/AP did not tell me what happened at the time as I think he was concerned about my reaction.
But it was enough of an event that I have remembered it ever since that day.

 

[Raymo]

I would guess the mixture control became disconnected due to a cotter pin not being installed, which would have allowed the nut to back off the carb lever.

 

[STEVE]

If the mixture control became disconnected the carb would go to full rich.

 

[Magman]

Don’t bet your life on it.

A152 has a MA-3A carb if I recall and no spring advance.

Nice idea though.

 

[Thad]

I would guess the mixture control became disconnected due to a cotter pin not being installed, which would have allowed the nut to back off the carb lever.

That sound scary. Have you heard of that happening often?

 

[Magman]

My thought is this should actually be a Pre-Start item.

Throttle, Mixture and Carb Heat should have “ cushion” ( aka Springback)

When full forward the stopping should take place at the Carb and the knob

should not contact the panel.

Not taught to pilots very often though.

 

[Raymo]

That sound scary. Have you heard of that happening often?

Not often but have heard of it happening. Usually resulting in an accident.

 

[Dhedeman]

If you forget to lock in the primer pump, the engine will go rough.

 

[Angie]

Not often but have heard of it happening. Usually resulting in an accident.

I found out that the owner/AP that was in the right seat during this had been very concerned about a possible crash since it started happening at a low altitude. I did immediately start eyeing the field on the other side of the interstate we add off the end of the runway.

 

[Magman]

An unlocked Primer will typically present at low power.

This is because the engine has LOW manifold pressure (HIGH vacuum)

and sucks the fuel through the unlocked Primer.

A 152 Primer System introduces fuel into the Intake Port of individual cylinders.

There may be 1.2,3 or 4 cylinders equipped with Primer Fittings.

Hence an unlocked Primer will provide additional fuel to all equipped

with the Fittings. So you may have a varying number of cylinders operating

in a “ too RICH” environment.

Increasing power increases Manifold Pressure which is LOWER vacuum

so the Primer introduces far less fuel and may not be noticed.

The somewhat similar C-150 has a different engine and Priming System..

It introduces fuel at one Primer Fitting that feeds ALL cylinders.


From the description the Primer is not the issue in this case.