Mysterious ignition problem [SOLVED]

1-877-473-6767, dial #2 to reach NGK support. You send them images of a suspect fake plug and they confirm whether it is or not. Champion may have the same service. Fake Chinee plugs are a real thing.....
 
JohnTW said:
Hi,

I have a strange problem with the GCV160A Honda engine on my Troy-Bilt 21-inch Push Lawn Mower (model: 11A-542Q711).

The engine started the first time (as always) and ran perfectly (as always) until the bag was full, so I stopped the engine, emptied the bag and went to start it again (w/o choking since the engine was hot), but it did not start.

So, I tried a few more times that day, but nothing.

I then tried a few days later but again, the engine wouldn't start.

Although this seemed like an electrical problem (since I never heard any sign of ignition / combustion like I usually do) I pulled the air filter and verified that the butterfly / throttle valve was moving freely. It was.

I then sprayed some carb cleaner directly into the carburetor in case there was a blockage in the gas line (which I was fairly sure was not the case because I could clearly smell gas after priming). I tried starting it again, but still no luck.

So I then removed the starter recoil assembly and the plastic cover to get at the ignition coil / magneto. I disconnected the spark plug wire, clamped the safety bar (dead man's handle), inserted a copper wire into the spark plug wire connector and positioned it about a millimeter off of the cast aluminum engine casing. I then rapidly rotated the flywheel back-and-forth such that the two magnets embedded in the flywheel would move past the two ends of the U-shaped magneto core to see if I could see a spark. I did this in the dark so that it would be easier to see, but never saw a spark.

Since the mower was apart I also tested the continuity between the little connector that goes to the kill switch and ground. When the dead man's handle was not depressed, there was continuity, and when you depress the handle, continuity is lost. I was glad that I saw a change because I didn't want to have to pull the flywheel to get at the switch.

I also verified that both magnets embedded in the flywheel were good (they both were able to firmly hold onto a steel socket).

So at this point I assumed the problem was a bad magneto and ordered a new one.

Well, I just installed the new magneto, reassembled everything and tried starting it again, but still nothing! It's a mystery as to why I'm still not getting a spark.

So let me ask the following question: Why does the dead man's handle *open* the circuit when depressed? Given that the little electrical tab on the magneto already shows continuity to ground (the engine case), what is the kill switch actually doing? To me it makes more sense if the kill switch would either: 1) keep the circuit open until the handle was depressed or 2) remove a (parallel) shunt across the coil when the handle is depressed.

I guess what I'm asking is: What is the high-voltage electrical circuit? One end of the magneto coil is clearly connected to the spark plug such that high voltage induced in the coil will jump the spark plug gap, return to ground, and then complete the circuit through the kill switch and back to the coil. Is that true?

Thanks,
John
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I agree with odd job. Had the same problem as you. It fixed it. Hope it works for you
 
When i was working at a small engine shop, had a lot of Honda mowers come in for not starting. Upon trying to solve the problem attempted to start the engine. Usually would pull the rope and have fire out the exhaust or back thru the carburetor, occassionaly it would rip the grip out of my hand. (ouch that hurt) Since they use a plastic cam and a drive belt some of the other techs would say to check the cam and the belt. Before I started operating I checked the plug it was a NGK so picked up a Champion installed it, tried to start it, It started and ran well. After a few more mowers not starting and causing the same issue I decided NGK stood for No Good Kind. Always used Champions and never had any issues.
 
Oddjob said:
In my experience with that Honda engine the culprit is often the spark plug. I don’t know why they fail so often, but they do. Put a new plug in there and see if that solves the problem. My guess is that you really heated up that engine making it mow and carry a heavy load on a hot day. You may have fried the plug. Best wishes, Oddjob.
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About 30 years ago I had a 4.5 or 5 hp Kawasaki with that problem. Every 3 years it would quit running. Plug would spark outside the combustion chamber so I initially thought it not the problem. After cleaning the spotless carburetor (no luck) tried a new NGK spark plug and it fired right up. For another 3 years, then I knew exactly what to do first.

That mower was replaced by one with a Honda GCV160 engine. Don’t think I ever replaced the spark plug. Checked the valves once. Air filter often. The problem I had with this one was the automatic choke. Hot engine stopped much more than 5 minutes would not restart because it was being choked. Had to wait 30 minutes to get it to start. Even so, I miss this mower. Started first or second pull every spring with untreated E10 in its tank all winter. Was in the habit of turning off petcock and running carburetor dry most every time I mowed.

That mower was replaced with a mistake: Snapper Ninja mulcher with B&S engine. Grass blew out from under the deck on the air filter side. Gas cap was designed so that grass which stuck to inevitable gasoline seepage would fall in the tank when cap opened. Right rear wheel height had to be adjusted by force with a screwdriver because it bound with the handle. Had to knock grass clippings out of the air filter every tank of gas. Speaking of which, used about twice as much as the Honda. Almost 1/3 acre per tank. A mistake.

Then that one was replaced with a 56V EGo. Much happier.

Moved, much bigger lawn. Now have a 61” Bad Boy Rebel with 27 hp Kawasaki, an 850 I think. Now it is behind me I don’t see it continuously to remember.
 
JohnTW said:
Oddjob and StarTech were right! It was, in fact, the spark plug. I changed it and the mower started-up immediately.

I learned something new. Thanks, gentlemen!

I marked this thread as SOLVED.

BTW, for others with the same problem, here's what I did:

- bought a BPR6ES plug
- removed the old plug with a 13/16" spark plug socket
- gapped the plug to 0.028" with a feeler gauge
- tightened the plug a 1/2-turn past hand-tight
- re-attached the spark plug wire

Cheers...
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Great news and very informative! Kiddos to those helping out!
 
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