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I've been having an intermittent issue with cylinders cutting out or weak. Here is a typical issue. I start the mower and it has a sputter. If I add choke it smooths out somewhat so I continue to mow. If the choke is off it smells rich. Adding the choke kinda clears it up. So with the engine hot I'll pull a spark plug wire to see which side is cutting out. So today I pulled the right bank plug and it keeps running without a change in sound or rpm. I put the plug back on. Then pull the left plug and it shuts off. Tells me the right cylinder is the issue. So I take it apart and get down to the coils. I clean and reset the gap. Put together and fire it up. Still the sputter and it still smooths out with a little choke. So I pull the left plug to see if it will shut down again. It keeps running. I put the plug back on and pull the right plug and it shuts off? So you'll see it randomly switches cylinder banks randomly.

This is a typical sequence going on for the past year. Every other time or two it will start fine and run on both cylinders.

One note, I usually use a temp gun to check external heat where the exhaust pipe connects to the head. Usually on the cylinder that seems cut out the temp is about 100 degrees lower. So to me it is generating some heat. When I pull the plug to the "dead" cylinder you can see a weak spark. On the cylinder that is working when I pull the plug there is a bright and active spark.

I thought about just buying parts until it's fixed but that is stupid. I have thought of buying two new coils but nothing indicates they are dead. I have also checked the connectors and cleaned them. I have not run any electrical diagnostics, electric baffles me, I'm more mechanical. Any ideas?

Thanks,
Doug

The wiring harness between the two modules with the anti talkback diodes could be getting wonky.

You need to determine whether you have a fuel or ignition problem. I would buy to inline spark testers (Harbor Freight) and install one in each cylinder. That way you can see if anything changes while running. Sounds to mean like you have a fuel problem, like bad gaskets or cracked manifold.

Rivets said:

You need to determine whether you have a fuel or ignition problem. I would buy to inline spark testers (Harbor Freight) and install one in each cylinder. That way you can see if anything changes while running. Sounds to mean like you have a fuel problem, like bad gaskets or cracked manifold.

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I'm not sure if I understand the logic behind your response. Not saying you are incorrect, I just don't understand. Each cylinder seems to run perfectly on it's own. Occasionally the both run great. Compression checks in the past revealed similar numbers. I have not done a check since last October and I didn't write down what they were. At the time they caused no alarm.

Thanks,

Logic is simple. Your problem could be in either the ignition system or the fuel system. Before fixing the problem you need to determine which one. Service techs test one system to say “It’s Good or it’s bad” Then proceed accordingly. Making assumptions, but not testing only gets us in trouble. Eliminating possible causes narrows down our search. Given what you have told us I would be looking at the ignition system first, but electrical problems are many times the hardest to resolve. With inline testers you will be able to quickly see if there are any changes in the ignition system while the engine is running. Based on past experiences I’d be looking for a bad, loose or corroded connection first and not throwing an parts at it until I’ve tested the entire system.

Rivets said:

Logic is simple. Your problem could be in either the ignition system or the fuel system. Before fixing the problem you need to determine which one. Service techs test one system to say “It’s Good or it’s bad” Then proceed accordingly. Making assumptions, but not testing only gets us in trouble. Eliminating possible causes narrows down our search. Given what you have told us I would be looking at the ignition system first, but electrical problems are many times the hardest to resolve. With inline testers you will be able to quickly see if there are any changes in the ignition system while the engine is running. Based on past experiences I’d be looking for a bad, loose or corroded connection first and not throwing an parts at it until I’ve tested the entire system.

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Thank you. Makes perfect sense. I suck at electrical but I have a killer Fluke Multimeter when I do

I would disconnect the "Kill" wires from the base of both ignition coils and see if the problem clears up. IF it does, your problem is in the "Kill wire" harness as suggested above. That is fairly common. You will then have to stop your engine from the test by pulling plug wires or shutting off gas by pinching the flexible fuel line if it is not equipped with a shut off valve.

Walt Conner

fairlaniac said:

Thank you. Makes perfect sense. I suck at electrical but I have a killer Fluke Multimeter when I do

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A test lamp is actually better
Multi meters give you numbers and those numbers just confuse people
I had some one insist his coil was reading 3.572 Ω which was 0.072 Ω too high
So I ran the wire brush over the terminals & fixed it so it read 3.451 which was in spec ( 2.5 to 3.5 )