Backfire on short final

[Jim Peace]

Now that all my avionics work is done and new engine cables and I have flown the plane about 30 hours etc. My tunnel vision is calming down and I am back to normal.  I noticed the last couple of flights that my engine is making what I can only assume is backfire noises from about 400 feet to touchdown.  Have not noticed this in the last 4 years of ownership.

I have a JPI 900 and will go over the data at some point this week.....

threads on this are kind of dated.

1964 M20c 180 hp carb

I am due for an oil change soon and will look over everything....but what should be concentrated on?

[Hank]

Mine sometimes burbles at idle power on short final, kind of like a 3/4 ton Ford truck I used to drive for work did when coasting downhill in town. It's never bothered me, but I've heard it may indicate a too-rich mixture for the weather at that time.

Edited June 21, 2018 by Hank

[mike_elliott]

3 minutes ago, Hank said:

Mine sometimes burbles at idle power on short final, kind of like a 3/4 ton Ford truck I used to drive for work did when coasting downhill in town. It's never bothered me, but I've heard it may indicate a too-rich mixture for the weather at that time.

Check for intake gasget leaks also

[Patto]

My C will make popping sounds if I run it rich during descent. Aggressive leaning eliminated it for me.

[gsxrpilot]

Yep, same in my C. I learned to leave Mixture off the GUMPS check. Just left it lean all the way to the ground. If I needed to go around, I could get both black and red knobs at the same time.

[Guest]

Possibly an intake leak from the recent engine work?

Clarence

[MarkC]

+1 to check for an intake leak.  This was the cause for me once.

Mark

[takair]

Check your idle mixture.  On shut down, see what the RPM rise is. Something less than 50RPM rise would be optimal.  If much more, it might be contributing to rich mixture and popping...

[jaylw314]

If it's a new thing, the warm summer temperatures might be contributing?

[skydvrboy]

8 hours ago, gsxrpilot said:

Yep, same in my C. I learned to leave Mixture off the GUMPS check. Just left it lean all the way to the ground. If I needed to go around, I could get both black and red knobs at the same time.

If I remember right, don't you do a GEEAR check instead of a GUMPS check?  Gear... Everything Else As Required.

[Jim Peace]

Took my plane to Air Mods in NJ.  Adjustments were made to the flux capacitor and got an oil change on a short 1 hour notice phone call......did not backfire on the landing back home....

[BDPetersen]

My Christen Eagle sounds like a corn popper when you pull the power on downwind and begin plummeting to earth. Never gets old.

[carusoam]

Hmmm....

1) I think technically a backfire comes out the carburetor...

2) Making this a frontfire? because it’s coming out the exhaust... (?) 

3) O360s are known for running rich at low MP settings...

4) The JPI data will be interesting to see what is going on during that portion of the flight?  Increased EGT until the flame goes out?

5) popping in the exhaust can be hazardous to its construction.  The interior of the muffler is at risk of getting broken...

6) An experiment to the procedure should show immediate results... Leave the mixture leaned some to see if the popping becomes less...

7) Be sure the mixture is full in, for the go around...

8) My M20C would pop a few times when I pulled the throttle back.  I experimented with pulling the throttle a bit slower to see if it would make a difference...

9) This is a good question for carb set-up... asking a mechanic familiar with the carb may be a good idea...  

 

PP thoughts only... not a mechanic...

Best regards,

-a-

[Hector]

My C was doing the same and it was an intake leak. Fixed the leak and popping went away.


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[Boilermonkey]

Mine does that if carb heat is onaking the mixture too rich.

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[Hank]

1 hour ago, Boilermonkey said:

Mine does that if carb heat is onaking the mixture too rich.
 

A hot summer afternoon will do the same thing.