# Sometimes Spark Sometimes No Spark



## orangputeh (Nov 24, 2016)

The carb problem I posted for my hs724 Honda is not the problem. It's spark. 

when i checked the spark before doing anything else it sparked. so i suspected the carb. after cleaning out carb it started right up. start up 10 times, it started first time 10 times.

let it set for a couple 3 days no start. my mistake was to suspect a dirty carb instead of checking spark.

tried today. no spark . it was a new plug so changed the plug anyway. no spark.

checked honda shop manual. 1st thing is suspect switch so i disconnected the black wire. no spark.

checked connector. cleaned etc. no spark.

wiggled bothe the spark plug boot which looks new and wiggled wire going into block.( on other side )

STRONG SPARK.

so connected everything and starts right up.

but i know this is NOT FIXED!. maybe just a fluke.

I'm sure some of you mechanics have run into this problem before so what is my next step. The manual suggests maybe a problem with coil but i have never dealt with that before.

i assume i have to take fan cover off and flywheel? or is there a simpler step i can perform to check maybe a loose connection inside?

or did i miss something more obvious?


----------



## micah68kj (Oct 8, 2011)

Something loose or possibly bare and shorting out? Any hungry critters maybe gnawing wires? Take a good light and physically check wiring. Hope you figure it out. Is moisture a possibility?


----------



## dhazelton (Dec 8, 2014)

I'd say the same thing, wire at magneto may be loose. When the engine is warm all connections expand you get spark. When cold things shrink and it's hit or miss.

Or else key switch - can you put a jumper across the wires there?


----------



## jsup (Nov 19, 2017)

Something is grounding out the coil. I had this happen on an older MTD. The "key" part rusted. When the key is pulled, it grounds out the spark, killing the engine. it rotted and hit against the cover, and would run intermittently. I replaced this key with a toggle switch with a rubber boot over it, marine type. Never had the problem again.

In your case, as stated above, I assume you have a real key, see if one of those wires is bare or lose, or if what it's connecting to has a brittle spot in the wire insulation. When wire runs by a hot spot on the engine, head, exhaust, etc, the insulation could become brittle, and it only takes a small break to make that happen. An easy way to solve it is to cut off the end connector and run shrink sleeving down the wire and shrink it around the existing insulation. Put on a new connector.

One way to catch this is to run the machine in a dark place, close the garage door and shut the lights, but not for long, you'll kill yourself. See if you see sparks anywhere along the kill switch system. 
i
Can someone post a schematic for this machine so we can look at it, it could help a lot.


----------



## vinnycom (Nov 6, 2017)

sort of lucky, carbs are finicky when not working right. electrical is either on or off, so either bad/loose/rusty connection(s) or bad wiring, imo easier to find and fix and/or replace components associated with it unless its the generator which im sure is not ur problem.


----------



## orangputeh (Nov 24, 2016)

dhazelton said:


> I'd say the same thing, wire at magneto may be loose. When the engine is warm all connections expand you get spark. When cold things shrink and it's hit or miss.
> 
> Or else key switch - can you put a jumper across the wires there?


i had a good key switch that I hooked up on that possibility. no go. when i got it running again I unhooked the switch and ground and started it and just grounded it out to stop. then hooked up key switch and it worked perfectly.

so i guess i'll have to dig inside. i know this is just a fluke fix until i find the problem because if i let it sit for a day or 2 , it probably won't start.


----------



## orangputeh (Nov 24, 2016)

jsup said:


> Something is grounding out the coil. I had this happen on an older MTD. The "key" part rusted. When the key is pulled, it grounds out the spark, killing the engine. it rotted and hit against the cover, and would run intermittently. I replaced this key with a toggle switch with a rubber boot over it, marine type. Never had the problem again.
> 
> In your case, as stated above, I assume you have a real key, see if one of those wires is bare or lose, or if what it's connecting to has a brittle spot in the wire insulation. When wire runs by a hot spot on the engine, head, exhaust, etc, the insulation could become brittle, and it only takes a small break to make that happen. An easy way to solve it is to cut off the end connector and run shrink sleeving down the wire and shrink it around the existing insulation. Put on a new connector.
> 
> ...


sorry, don't understand. are you talking about the key switch at the control panel? I changed the switch and same problem. 

i'm not sure what got my spark back since i wiggled the spark plug boot and the wire going into the fan cover at the same time. i just know something is loose or something else. it works and sparks sometimes and then sometimes not.


----------



## jsup (Nov 19, 2017)

orangputeh said:


> sorry, don't understand. are you talking about the key switch at the control panel? I changed the switch and same problem.
> 
> i'm not sure what got my spark back since i wiggled the spark plug boot and the wire going into the fan cover at the same time. i just know something is loose or something else. it works and sparks sometimes and then sometimes not.


I'm speaking in generalities because I don't have a schematic to look at.

Typically these key switches are normally closed switches, meaning in the off position the circuit is complete.

When you turn the key ON, the circuit is incomplete or open. 

Typically, these switches have the negative side of the ignition coil on one side of the switch, and ground on the other, grounding the short when the circuit is completed (turned off) killing the spark, and thus killing the engine. 

So on one side of the switch is a wire that should go, again typically, to the ignition coil negative, the other side of the switch goes to ground. Anywhere around that circuit the wire can chafe, get brittle, and short to ground, causing all kinds of problems, especially the kind you describe. 

Now, you said you moved the spark plug wire around and the problem went away. Another place that can ground, wear, crack, or chafe, is the spark plug wire itself. Inspect the spark plug wire see if it is dry and brittle, that could be causing your spark to jump past the insulation to ground, resulting in no spark condition.

Again, the best way to witness this is in a dark room with the engine running. You'll see the sparks. Not to long, or leave a note it was an accident. 

I believe the spark plug wire is integral to the coil, so if that's it, you'll need a coil. A solution for this would be a piece of plastic wire loom wound with two passes of electrical tape. There's 3 kinds of loom, you would get the one with the white or green stripe. Green being the best, it's heat rated and would work best on a sparkplug wire. However, just as a test of the sparkplug wire, put any piece of scrap hose around it, tape it over with electrical tape, and see if it's more reliable. 

It's hard to say anything for sure without a schematic, these are general guidelines. This is why I like wire loom, it keeps chafing and wearing of wires to a min. I loom everything, I keep 100s of feet in 3x3 foot rolls in the garage.


----------



## JayzAuto1 (Jul 25, 2016)

Does that engine have a low oil sensor and kill module?? Many Honda's do and can give those symptoms, ESP if low on oil. Maybe something to check??

GLuck, Jay


----------



## jsup (Nov 19, 2017)

JayzAuto1 said:


> Does that engine have a low oil sensor and kill module?? Many Honda's do and can give those symptoms, ESP if low on oil. Maybe something to check??
> 
> GLuck, Jay


Good thought. Defective oil level switch.


----------



## orangputeh (Nov 24, 2016)

jsup said:


> I'm speaking in generalities because I don't have a schematic to look at.
> 
> Typically these key switches are normally closed switches, meaning in the off position the circuit is complete.
> 
> ...


thank you very much. i'll check those things and come back when and if I find the solution.


----------



## orangputeh (Nov 24, 2016)

jsup said:


> Good thought. Defective oil level switch.


maybe. the oil was recently changed and is okay. what is the location of the oil level switch if the hs724 has one?


----------



## jsup (Nov 19, 2017)

orangputeh said:


> thank you very much. i'll check those things and come back when and if I find the solution.


A battery and a test light could help, or a multi-meter with a continuity buzzer. You can use the test light in series with a battery, or use the continuity buzzer.

Connect the continuity meter to one side of the switch, leave the switch off, you should get a buzz for continuity across the switch or to any ground. Turn the key, the buzzer should stop, because it's open. If it doesn't, that's your problem, in the key circuit. (again in generalities, don't know if Honda is any different, don't see why it should be.)

follow wires physically from the switch, see if you hear a buzz, indicating a short, that would be the problem. Electrical gremlins, especially intermittent ones.

I hope this helps.

If anyone knows the spec on how to test the low oil sensor, that's a good place to look too. That's very possible. Will the Hondas run without a low oil sensor if he disconnects it.


----------



## drmerdp (Feb 9, 2014)

The lighting coil is under the fly wheel but the ignition coil is right on top. Just remove the recoil starter and Shroud.

I think there is a single black wire that goes only to the key switch. Inspect wire for a short.

Next is to ohm out the primary and secondary windings with a multimeter. Your service manual should have these specs and maybe show how to check it. The coil may spec correctly some of the time and not when it’s in failure mode. Try to test it when it’s not starting. 

Primary winding is tested by checking the resistance from the spade terminal (black wire to switch) and the metal body.

Secondary winding is tested by checking the resistance from the spark plug wire to the metal body. 

Off the top of my head specs are 
primary 1.2k ohms
Secondary 10k ohms


----------

