6 Horse Briggs Spark Is Orange Should It Be Blue

Joshua Heling

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Aug 20, 2016, 11:26:05 PM 8/20/16

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Hi Sector-folk -

I'm an engine repair novice, but am trying to learn and troubleshoot an old walk-behind brush cutter that sometimes doesn't start.  While I was posting the following summary of my problem to various forums, it occurred to me that there might be a sector67 member with an idea about what next steps I should take.

I'm either just knowledgeable enough to be dangerous, or stupid enough to try to DIY this fix.  Or maybe those are the same thing. ;)  Either way, I've probably checked some things that don't need checking, and could well be missing something.

Symptoms:

* The engine has, for a few months, failed to start reliably.  Oftentimes it would start right up, but once in a while it would crank and fail to turn over.  Seemed random, but would start quickly 4 out of 5 tries.

* Sometimes this changes for a period of time (days to weeks), in which it consistently won't start.

With a spark plug tester hooked up during the times that it won't start, I see only a weak spark.  Orange; not a hint of blue.  I suspect, but do not know for sure, that a weak spark is why it's not starting.  When it _does_ start, there's still no blue in the tester - just a stronger orange.

Things I'm pretty sure of:

* The battery is good.  The battery is about 18 months old.  I initially thought this might be a battery problem, so took it in to the battery store who tested it and found strong CCA and voltage.

* Fuel delivery.  I can see fuel moving through the filter when I try to start it, and the inside of the carb had fuel when I took it apart to check.

* It's not the kill switch.  I've detached the kill switch from the ignition coil and see the same symptoms.

* It's not as simple as a bad spark plug.  I proactively replaced a plug about a month ago when doing some general maintenance work, and then when it stopped starting completely got another plug just in case there was something wrong with the replacement.  So I now have three spark plugs that all work the same, and show the same results in the spark plug tester.

I suspect that the problem is either a bad ignition coil or the flywheel.  The flywheel is very rusty (the engine is pushing 20 years old), and I've read (conflicting) reports that that might be a problem.  Or maybe it's the ignition coil?  I have no reason to suspect that other than process of elimination.  Is there any way I can test it?

Other background: Nothing in particular happened between the time it would mostly start and when it stopped starting at all.  A couple of weeks before then, I did a bunch of general maintenance - new fuel filter, cleaned the air filter, thoroughly cleaned the exterior of the engine, sprayed some carb cleaner in the carb, changed the oil.  One of the bolts on the case rocker in front of the head cylinder seems to have some thread damage, and was leaking some oil, so I added some thread sealant and the leak is much, much slower.  I have checked and reset the air gap between the ignition coil and the flywheel to .012".

At this point, I'd love suggestions about what to try next.  Ignition coil?  Flywheel?  Something else?

Thanks,

Josh

Alec M

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Aug 21, 2016, 1:08:03 AM 8/21/16

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Try tracing the second (non spark plug) connector, and see where it goes.
Usually it just goes to a primitive sort of switch, which grounds the ignition coil to the body of the engine when the handle is gripped.
If that's not working the ignition coil won't necessarily work, but in the worst case scenario, yes you might have to replace the flywheel.

I hope you can get it working!

-Alec

Joshua Heling

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Aug 21, 2016, 2:46:10 AM 8/21/16

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Thanks!  If I follow correctly, you mean the wire connecting to the ignition coil that _isn't_ the spark plug lead, right?

I think I've separated that from the problem by removing that connector completely and observing the same behavior.  (This is what I meant by the "kill switch" - the operator presence lever.)  Does that make sense?

thanks,

-jrh

Chris Meyer

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Aug 21, 2016, 2:49:38 AM 8/21/16

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Put a new coil in it and it will probably fix the problem.  If you want to test the theory then put the engine in a dark location and try starting it, spritz water on the coil/coil lead and see if it dies or has visible sparking.  If it's wet and will no longer work (or if it's humid outside), take it inside and carefully dry it with a hair dryer (not a heat gun unless you're a long way away) and try again.  Coils typically delaminate/have epoxy crack over time and it allows water in which kills the effectiveness of the coil.  Otherwise the insulation on the line can also break down over time and allow the spark through the side of the wire or around the plug boot.

Chris

Joshua Heling

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Aug 21, 2016, 3:44:39 AM 8/21/16

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Oh, that's interesting!  I wouldn't swear to it, but it's entirely possible that the humidity has correlated to the symptom flaring up.

So in that test you describe, I spritz while trying to start it, yes?

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Alec M - Builder of all things floppy drive related

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Aug 21, 2016, 8:15:17 AM 8/21/16

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Yes, I was talking about the wire you're thinking of, I just wanted to make sure that wasn't the problem, since I thought I had seen something about that connector online back when I was
Chris's suggestion is a good one, I have a Briggs and Stratton lawnmower that didn't spark, all it took was a new ignition coil. the old one was rusty and the enamel was starting to look weird.Hopefully

-Alec

Joshua Heling

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Sep 11, 2016, 10:20:31 PM 9/11/16

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Following up:  A new ignition coil appears to have totally fixed the problem.

I was hoping to confirm the humidity theory by causing it to stop working with the water spritzing routine, but I wasn't able to get it started to run the test (thanks; midwestern humidity) - I didn't try the hair dryer.

In any case, it sprung to life once the new coil was in.  Thanks!

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