Backfire

[Sparkey 40]

Wheel horse c125 with a Kohler . What do I need to do to stop it from backfiring when I turn it off ? Is this a carb adjustment ? I idle it down which helps sometimes.

Thanks 

[wallfish 17,778]

Try leaving the throttle at full and engine running full speed and shut it off.

[ebinmaine 71,597]

2 hours ago, wallfish said:

Try leaving the throttle at full and engine running full speed and shut it off.

 

Or similar... I shut off Cinnamon at low idle and as soon as the key is off I put the throttle lever to high.

Something to do with releasing pressure so raw gas doesn't flow/burn?

 

It works....

[WHNJ701 4,165]

I know the 411-4 backfires unless you run it at low throttle for a few then shut it down.  been that way since new in 89

[953 nut 58,997]

Could be running too hot, remove the engine tins and clean between the cooling fins. Also, use a timing light or static timing to be sure the ignition timing isn't causing overheating.

[Tuneup 1,442]

Hi there, Sparky,

 

My '80 125 plays the same game. Yesterday, in fact, I ran it a little richer than usual. Fins clean on a rebuilt engine with original and clean carb. If I let it idle extensively, it will shut down cleanly...not usually. I get a strong pop more often than not, and as yesterday after a 30 second idle. I wonder if we can apply the world of radial engine control to this issue. When killing a radial, you never kill it lean - you run to full rich to eliminate the possibility of a backfire that will blow the complex exhaust. So, idle, full choke, ignition off. Remove the oxygen component in the muffler and reduce ignition. It won't run long enough to have the added fuel input to dilute the cylinder wall coat, etc. Heck - I have a new, strong muffler so will give a try today!

 

OK, all that said, the 80 will always pop on a throttle down. My '77 will not pop on throttle down and has never backfired at off. Muffler has not mattered so we'd have to look at the intput. Same model carb and fresh gaskets so YMMV. Heading into the off season, it's time to soak the 80's carb (again).

[wallfish 17,778]

6 hours ago, Tuneup said:

Hi there, Sparky,

 

My '80 125 plays the same game. Yesterday, in fact, I ran it a little richer than usual. Fins clean on a rebuilt engine with original and clean carb. If I let it idle extensively, it will shut down cleanly...not usually. I get a strong pop more often than not, and as yesterday after a 30 second idle. I wonder if we can apply the world of radial engine control to this issue. When killing a radial, you never kill it lean - you run to full rich to eliminate the possibility of a backfire that will blow the complex exhaust. So, idle, full choke, ignition off. Remove the oxygen component in the muffler and reduce ignition. It won't run long enough to have the added fuel input to dilute the cylinder wall coat, etc. Heck - I have a new, strong muffler so will give a try today!

 

OK, all that said, the 80 will always pop on a throttle down. My '77 will not pop on throttle down and has never backfired at off. Muffler has not mattered so we'd have to look at the intput. Same model carb and fresh gaskets so YMMV. Heading into the off season, it's time to soak the 80's carb (again).

 

Did you ever try shutting it down on full throttle instead of all the idling down?

I know this sounds counter productive but it works for mine and believe there may have been a service bulletin stating to do this.

[Tuneup 1,442]

And so, maybe the same result as the old Mustang flyer. Idle, full choke and ignition off. Nice shot of flame out the exhaust but no pop!

 

[Sparkey 40]

Will give the suggestions above a try and report back 

Thanks guys !

[AHS 1,520]

My ‘73 14 hp, full throttle, ignition off, it will backfire! If I throttle it down for 30 secs..it won’t backfire.

[bc.gold 3,406]

On 9/21/2019 at 10:24 PM, jabelman said:

I know the 411-4 backfires unless you run it at low throttle for a few then shut it down.  been that way since new in 89

 

Poor grade of gasoline, think ethanol.

 

ENGINE BACKFIRES

Water or dirt in gasoline.

Engine cold

Poor grade of gasoline.

Sticky inlet valves.

Overheated valves.

Spark plugs too hot.

Hot carbon particles in engine.

 

 

[bc.gold 3,406]

A list of fuel additives that have been tested were taken from this article/

 

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=12&ved=2ahUKEwjC-PnenffkAhXRv54KHTflC5UQFjALegQIBxAC&url=https%3A%2F%2Fcropwatch.unl.edu%2Fdocuments%2FEthanol%20and%20Water%20Contamination%2009052014.pdf&usg=AOvVaw2cxyl5lamlSQ8bAgN3YbDg

 

Ethanol and Water Contamination: Results and Observations
F. John Hay*, Igor Maxiamiano Sousa**, Ivan Freitas Makino**
*University of Nebraska Lincoln Extension Educator – Energy
**University of Nebraska Lincoln – Undergraduate Intern

 

Abstract:
Ethanol is hygroscopic, gasoline is hydrophobic. Water contamination in fuel can cause engine
non-starting and corrosion issues. Ten percent ethanol blends can hold small amounts of water
in solution, above this level a phase separation of water and ethanol mix separates from the
gasoline. Many fuel additives claim to solve this phase separation issue or claim to dry the
gasoline, remove water, etc... This study endeavored to determine the amount of water
ethanol blended fuels can hold in solution and determine the efficacy of common additives in
their ability to increase the amount of water held in solution. Based on results from small 8 ml
test tubes and larger 100 ml jars E0, E10, and E15 can hold Zero, 0.41% and 0.85% water
respectively. Two of 8 tested additives increased the amount of water held in solution.
 

 

Additives
STP:
Amount used: 336μ (3.36 μ/ml)
Solved the problem? No

 

BG – Ethanol Fuel System Drier:
Amount used: 468μ (4.68 μ/ml)
Solved the problem? Yes
Maximum held: 0.43%. Separated again at 0.44%.
The addition of this additive increased the water holding by 0.23 tsp per gallon, a 7% increase
over E10

 

ISO-HEET:
Amount used: 469μ (4.69 μ/ml)
Solved the problem? Yes
Maximum held: 0.43%. Separated again at 0.44%.

 

STABIL – Ethanol Treatment:
Amount used: 315.5μ (3.157 μ/ml)
Solved the problem? No

 

Rislene
Amount used: 664μ (6.64 μ/ml)
Solved the problem? No

 

Heet
Amount used: 469μ (4.69 μ/ml)
Solved the problem? Partially

 

Seafoam
Amount used: 781μ (7.81 μ/ml)
Solved the problem? No

 

Valvoline Nitro Shot
Amount used: 200μ (2.0 μ/ml)
Solved the problem? No

 

Edited September 30, 2019 by bcgold

[ebinmaine 71,597]

Answer.

Don't use ethanol.

 

 

53 minutes ago, bcgold said:

Hot carbon particles in exhaust.

 

This is what causes my c160 to fire after ignition off.... Problem solved by opening throttle at shutdown.

 

 

 

[jebbear 386]

8 minutes ago, ebinmaine said:

Answer.

Don't use ethanol.

Amen to that! I've been using ethanol free gas ever since I found a local station that carries it. More expensive, but saves a lot of headaches with carbs and fuel pumps, etc. too.

[bc.gold 3,406]

This is from the Wisconsin shop manual and would hold true for any air cooled engine regardless of brand.

 

If the engine has been running hard and is hot, do not stop it abruptly from full load, but remove the load and allow engine
to run idle at 1000 to 1200 R.P.M. for three to five minutes.

 

This will reduce the internal temperature of the engine much faster, minimize valve warping, and of course the external
temperature, including the manifold and carburetor will also reduce faster, due to air circulation from the flywheel.

Dieseling, is caused by the carbon deposits in the cylinder head being heated up to such an extent that they continue to
fire the engine and keep it running after the ignition has been shut off.

 

By idling the engine, as previously mentioned, the carbon deposits cool off, break up and will blow out through the exhaust.