Misfire

E

Eggbert

Member
Something has happened to by lawn tractor with its 24 Hp v-twin Kawasaki. I've only used it a few times this year and it was fine for a while. Now it has started to misfire/backfire. Happens around 3 or 4 times in a row, then runs normally for a few seconds, then repeats.

Yesterday I wire brushed the plugs and cleaned the float bowl, needle and seat. It ran fine for about 45 minutes, then started the misfire again, but not quite so violent.

In both cases this seems to happen after it has run for a while.

Both plugs look identical, but are oddly brown. That's why I wire brushed them. So new plugs are no doubt a good idea, however I suspect a coil. Oddly I just replaced both coils. Might have been last summer, or possibly the summer before. No doubt the coils from Amazon weren't good quality, but they worked until now.

My mower is stored outside and it does get cold in the winter. I've had coils go before from freezing then thawing and repeating this, but my experience has been with single cylinder engines so they just die.

Any thoughts before I start throwing money at this issue?

PS: I goofed. I replaced both coils in August of 2023, so they're older than I thought.
 
My advice would be to get some good diagnostic experience or hire someone that already has diagnostic skills as opposed to throwing good money at guessing.
 
you never wire brush the tip of spark plugs. The ceramic will pick up metal off the wire brush and short out the plugs. Now you need new plugs. Do not buy them online because of all the counterfeits. Get them from a local place like NAPA or your local mower shop. No torch brand.

Run some HEET or something like that in the fuel to see if you have a little bit of moisture in it. Check for rodent nests and wire chewing,
 
Okay.... Let's keep it simple. Don't pull out the credit card yet.

What is the equipment you are working on?

A product ID label picture would help. Kawasaki did not build the chassis this engine is mounted on. We need a better idea of the "whole picture" without the blinders focused only on the engine. Running problems are not limited to just the engine alone.

When it misses while hot, does it also lose power? If so, have a spray bottle with water standing by to spray each exhaust outlet pipe. Water will burn off quickly if the cylinder is producing power. If one is slow to burn off the water, that is the side to look at closer. It can be ignition of fuel related.

I cannot fault an Amazon ignition coil at this time, but it is suspect. Ignition coils do get moody with heat. Many aftermarket coils are wound with copper-clad aluminum-core wire which is garbage wire that fails after a couple of years.

Plugs from Amazon are copycat garbage most of the time, so use only plugs from a parts store. Remember cheap prices do not mean quality or reliability.

More common than not is a fuel related issue.... Never assume your fuel storage can is perfectly clean inside. These problems often start at the fuel can and eventually end up in the fuel tank most of the time, but people tend to work backwards by starting at the carburetor. I've seen and read about many carburetors getting replaced that had nothing wrong with them, the fuel supply to the carb was the issue.

Over the years, grass chaff a dust slowly make their way into the fuel cans and equipment fuel tank and collect in the bottom of the fuel tank on machines. At first, this stuff only shifts around, but eventually it gets draw into the fuel pickup tube or gets lodged in the fuel line.

If your fuel is over 6-months old (even with stabilizer) it needs to be sucked out and put in your vehicle gas tank. Replace the gas with new mid-grade fuel from a good fuel station and not some budget "mom and pop" station.

Let us know your progress. It does no good to write you a "book" with a thousand thing to test and inspect. Let's move systematically if you have the patience.

If you don't have the patience, haul it off and buy a new machine.... That's what the equipment manufacturers wants everyone to do these days.
 
Hello T.,

If you are in South Texas like me, it does go bad faster than most people realize. Sitting in a fuel can out in the sun and in the back of a pickup truck just makes it happen faster.

Just wait and see all the fun we are going to have with the rollout of E15 fuel that is coming.

Ethanol blended fuels are developed for automotive use anyway and not meant to be used in anything with a carburetor or sits around most of the time.

The fuel without Ethanol cost more and people typically do not realize the benefits of using that.
 
Ever thought about this? Mixing 15% Ethanol blend with non Ethanol fuel at 50/50. That would bring the E15 down to an E7.5. Still more expensive but less expensive than completely E0 fuel.
 
sgkent said:
you never wire brush the tip of spark plugs. The ceramic will pick up metal off the wire brush and short out the plugs. Now you need new plugs. Do not buy them online because of all the counterfeits. Get them from a local place like NAPA or your local mower shop. No torch brand.

Run some HEET or something like that in the fuel to see if you have a little bit of moisture in it. Check for rodent nests and wire chewing,
Click to expand...
You had me until you mentioned Heet. (y)

Just drain the entire fuel system and carb bowl. Replace with fresh non E-10 juice and stabilizer. Not like you are draining a container ship here. I see no need to throw band-aids at some suspect fuel which is probably stale and full of water.
 
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Auto Doc's said:
I cannot fault an Amazon ignition coil at this time, but it is suspect. Ignition coils do get moody with heat. Many aftermarket coils are wound with copper-clad aluminum-core wire which is garbage wire that fails after a couple of years.
Click to expand...
What about all the oil, dirt and grass covering said coil? Mummy wraps the coil holding in all that heat. Good way to burn one out or degrade the spark.
 
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