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T. Phoenix
T. Phoenix, Technician
Category: Small Engine
Satisfied Customers: 539
Experience:  10 + yrs. working at family shop
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What causes weak spark besides bad magneto

Resolved Question:

What causes weak spark besides bad magneto?
Submitted: 6 years ago.
Category: Small Engine
Expert:  T. Phoenix replied 6 years ago.
Hi There!
Thank you for letting me try and help you here.

A bad coil, spark plug wire, spark plug and flywheel magnets can all cause this.
If the engine is old enough to have points, a dirty or worn set of points and condesor can cause it.
Customer: replied 6 years ago.
The Mower is only 1 year old.
Expert:  T. Phoenix replied 6 years ago.
Have you tried a new spark plug?

Shoot a little gas in the spark plug hole and see if it fires off with a new spark plug.
Customer: replied 6 years ago.
What spark plug should be in the mower? (#)
Expert:  T. Phoenix replied 6 years ago.
What engine does it have? Model, Serial, numbers?
Customer: replied 6 years ago.
675 series Serial# XXXXX 126T05-0841-E1 Model # XXXXX 06122157 Briggs & Stratton
Expert:  T. Phoenix replied 6 years ago.
Briggs and Stratton 697451 is the OEM recommended plug.
Customer: replied 6 years ago.
I don't have a Briggs OEM spark plug, I have a Champion J19LM, is that the right equivelent to the Briggs specification?
Expert:  T. Phoenix replied 6 years ago.
Yep that will work fine. As long as it's new. Plugs can foul and go bad even if they look fine.
Besides honestly it's the cheapest part you can change to see if it helps.
The next step would be the coil.
Customer: replied 6 years ago.
Isn't the coil part of the Magneto? I've changed that still get same results and the motor has to be spinning pretty fast to produce that weak hairlike spark, Is it possible that the flywheel just has factory defective magnets (weak magnets) I tested magnetivity with a flatblade screwdriver ,seemed strong enough.
Expert:  T. Phoenix replied 6 years ago.
What color is the spark?
Customer: replied 6 years ago.
Bluish orange
Expert:  T. Phoenix replied 6 years ago.
orange is typical. Blue is exceptional.
If you have somewhere inbetween then you have good spark.
The spark on a spark plug is tiny anyways.
Are you having a problem to to prompt you to look into this?
Customer: replied 6 years ago.
Yes ,very hard to start ,I've had it into the shop,they told me there was just leaves packed underneath. It has elec. start and pullstart and I pull til my arm is sore and still won't start, when it does finally start it misses and yes I checked the shearkey on the flywheel.
Expert:  T. Phoenix replied 6 years ago.
Ok several things can make an engine hard to start.
Of course a bad spark plug, dirty or out of adjustment carburetor, low compression, valves needing adjustment, cranking speed to slow, dirty air filter, clogged exhaust, intake air leak, and old gas.
Have you checked all those things or did the shop when it was there?
Customer: replied 6 years ago.
The carb. is non adj. factory set, the spark was tested with a spark checker on two different magnetos,even tested mag. on different mower and got good spark, air filter was cleaned,and compression good (93 psi). The mower has only been used 4 times since purchase.
Expert:  T. Phoenix replied 6 years ago.
Hey I'm not one to dispute the facts.
If you put the mag on a different mower and you had better spark then you just might have a bad flywheel.
Customer: replied 6 years ago.
Is there a way to test the strength of the magnets other than with a screwdriver?
Expert:  T. Phoenix replied 6 years ago.
No
Customer: replied 6 years ago.
Too bad my warranty is up, I guess I'll try another flywheel ,thank you so much for your time.
Expert:  T. Phoenix replied 6 years ago.
Sure thing,
Come on back if you need anything else.
T. Phoenix and 2 other Small Engine Specialists are ready to help you