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Small engine won't start unless plug changed.

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BrianC View Drop Down
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Joined: 16 Jun 2011
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Post Options Post Options   Thanks (0) Thanks(0)   Quote BrianC Quote  Post ReplyReply Direct Link To This Post Topic: Small engine won't start unless plug changed.
    Posted: 17 Nov 2020 at 3:50pm
Ok the mysteries of the spark plug is bugging me.
Honda GX120 on a water pump, it runs all the time (de-watering duty)
Then it stops. Pull plug, yes a little oily and carboned, check gap, lay on block, hand crank,
we get what looks to me like a good spark.
Put it back in, NOTHING, even with ether.
Replace the plug with brand new plug (same BPR6ES model plug), it starts.
Run it for a few hundred hours then same cycle.
With new plug it goes, old plug, nothing.
So I have read that fouled plugs will fire out of engine, wont fire under compression.
Is this what I am experiencing?
Could the coil be weak?

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DMiller View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote DMiller Quote  Post ReplyReply Direct Link To This Post Posted: 17 Nov 2020 at 3:59pm
Likely eating just a little oil, that with the IMPROVED compounds to make gas burn get deposits on insulator of plug.  Have used a Brass small gauge wire brush on plugs as this and gotten more use, in the Olden Days had a AC Spark Plug Cleaner to run them thru a few times.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jaybmiller Quote  Post ReplyReply Direct Link To This Post Posted: 17 Nov 2020 at 4:00pm
a 'good' spark in open air should be bright blue and BIG.....
any 'oily' plug is fouled...
getting a few HUNDRED hours on one plug is GREAT....

if you take the 'bad' plug, clean with brake cleaner and wirewheel, does it fire ??
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steve(ill) View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote steve(ill) Quote  Post ReplyReply Direct Link To This Post Posted: 17 Nov 2020 at 4:24pm
I worked at a Honda Motorcycle shop 45 years ago.. What you describe is VERY COMMON... When one "would not start", the FIRST thing we did was put in a plug.. If that didnt work then you check timing and fuel...  FOUL OUT under compression was very common.... I worked on a Honda 4 cylinder car one winter.. FLOODED and COLD... no new plugs as an option.. Took them inside and BAKED in the oven at 250 degrees for 30 minutes.... and it started !!
Like them all, but love the "B"s.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote TMiller/NC Quote  Post ReplyReply Direct Link To This Post Posted: 17 Nov 2020 at 5:05pm
Harbor freight has an air spark plug cleaner about $20, works good.  Use ohm meter on "highest" setting and check for continuity between electrode and base, should not have any continuity as would indicate a short.
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BrianC View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote BrianC Quote  Post ReplyReply Direct Link To This Post Posted: 17 Nov 2020 at 5:42pm
Thanks, I can let this one rest. This is what the world means by "fouled spark plug".
But it just seems that in the latter years, plugs and ignitions in general
work better. Brigs came out with that pointless (Magnastart or such) system  in the '80's
and ignition problems went away for me. My personal lawn mower only gets about 30 hours per year, and I replace the plugs like every other season. But this water pump engine gets a lot of hours.

Also, I was wondering if the engine could be getting tired.
The Honda GX120 is an OHV with cast iron liner-about how many hours might it last
in this constant load water pump duty. 1000, 2000,...?
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steve(ill) View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote steve(ill) Quote  Post ReplyReply Direct Link To This Post Posted: 17 Nov 2020 at 5:57pm
thats kind of a loaded question... An el cheapo B&S in a push mower might get 300 hours. A mid size , base line, riding mower may get 1000 hours.. Some of  better quality riders with motors that have oil filters and pressure lube are up to 2000 - 2500 hours. The highest quality industrial line motors can get 4000 hours...  A lot depends on the application, how many years it is stretched out, maint , oil changes, etc... That GX120 Honda with OHV and cast liner is an above average motor... 1000 hours should be a minimum.. Dont know if i would plan on it making it to 2000.............. 1500 ?

Edited by steve(ill) - 17 Nov 2020 at 5:59pm
Like them all, but love the "B"s.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Dale (Stonelick) Quote  Post ReplyReply Direct Link To This Post Posted: 17 Nov 2020 at 7:34pm
I used to change the fouled plug annually in my cheap push lawn mower.  Last few years I use Mechanic-In-A-Bottle (or equivalent) in each tank of gas, which keeps the plug clean.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Stan IL&TN Quote  Post ReplyReply Direct Link To This Post Posted: 18 Nov 2020 at 3:35pm
Start running a hotter plug in it. Might not cure it but it should help.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote HD6GTOM Quote  Post ReplyReply Direct Link To This Post Posted: 18 Nov 2020 at 6:59pm
Wanted to clean up in the yard today, 60° today an the dang JD mower wouldn't fire a lick. Tried it 5 or 6 times. Will take the weed eater and finish it tomorrow. 1st time in 10 years it failed to run.
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Walker View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Walker Quote  Post ReplyReply Direct Link To This Post Posted: 18 Nov 2020 at 7:08pm
Check to see if the magnet on the flywheel has a layer of rust on it. A piece of sandpaper  will fix it.
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marion View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote marion Quote  Post ReplyReply Direct Link To This Post Posted: 20 Nov 2020 at 8:02am
had same problem with 24 hp honda engine, started runninng purple racing fuel with lead in it, just about cut my fuel usage in half, ran better than ever and never changed a plug again. 
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ac fleet View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ac fleet Quote  Post ReplyReply Direct Link To This Post Posted: 20 Nov 2020 at 10:31am
so where would you get purple racing fuel out here on the tundra??? ---- just askin----
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Coke-in-MN Quote  Post ReplyReply Direct Link To This Post Posted: 20 Nov 2020 at 9:27pm
try your local airport for small planes - aviation fuel runs good in many things - well as long as you don't use 115/145 Av Gas - everyone i know that tried that in their cars had problems shortly - military grade fuel with a 5 finger discount 

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Coke-in-MN Quote  Post ReplyReply Direct Link To This Post Posted: 20 Nov 2020 at 9:33pm
Champion interchange - but I would forget using a resistor plug and go with N series like N7YC
    Details about NGK BPR6ES:
  • Threaddiameter: 14mm
  • Threadreach: 19mm
  • Seattype: flat
  • Hexsize: 21mm
  • Tipconfiguration: projected
  • Construction: Standard construction
  • Terminaltype: Removable


Edited by Coke-in-MN - 20 Nov 2020 at 9:35pm
Faith isn't a jump in the dark. It is a walk in the light. Faith is not guessing; it is knowing something.
"Challenges are what make life interesting; overcoming them is what makes life meaningful."
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