Briggs & Stratton lawn mower with no spark.

[Joe Soy]

Greetings Lawn World,
I have an old Craftsman lawn mower with Briggs and Stratton 5.5 engine (Model # 128802-1519-23, yes, very old). I was having problems starting so upon examination, found that the primer bulb was cracked. I replaced that and while I was at it, changed the oil and spark plug. It started and ran great for one time only. The next time I could not start it. I have fuel and air so I fell upon the spark as an issue. I tested the ignition coil as per directions on YouTube (With the kill switch connected and unconnected) and found no spark. I bought a new induction coil but still no spark. I should say there is a very weak to non-existent spark, if I hold the plug in my hand I get a very weak jolt sometimes. I set the air gap on the coil with a business card that measured .010" with a caliper and also bumped it down to .006" with a feeler gauge. No luck.
I am grasping at straws to find a solution as there seem to be no other electrical components evident.

Could I really have Two bad induction coils?
Do I need to insulate the coil on the bottom where it mounts to the engine?

 

[davbell22602]

Have you checked the flywheel key? How much compression does it have? Is the engine stop cable stretched? Air gap is .010 on a Briggs coil.

 

[Joe Soy]

davbell22602,
I have not checked the fly wheel key as the fly wheel turns easily with the spark plug out and the piston moves and the valves open and close as I turn the crank. The stop cable does not seem to be stretched, it pushes rather than pulls, the brake is completely off the fly. When I get a chance I will check the compression. It's an old engine so,,,
As stated before I'm grasping for an answer but it seems that logically, either there is little spark generated or the spark is running straight to ground. Induction is induction, I should be able to pass a strong magnet over the coil and generate a spark via magnetic flux. I'm wondering, I've been turning the fly by hand, if I could turn it faster would this make a difference in the strength of the spark, i.e. a sharper spike so to speak? Or am I thinking too much? The air gap is set to .010". Thanks for the reply.

 

[Rivets]

Could you have install the coil upside down, the kill terminal should be down close to the block? It has happened. Also, do not insulate the coil, the two mounting bolts provide you ground. I doubt you have shear a flywheel key, as you would still get a hot spark, but at the wrong time.

 

[Joe Soy]

Rivets,
No, the coil is right side up. If you look closely at the picture you can read "This side out" or something and the kill connect is on the bottom. Although it would be easy to install it upside down. My tools will stick to the magnito but I wonder, do they lose their magnetic strength over time? Seems unlikely.

 

[EngineMan]

Can you re gap to .015" and see if you get spark.

 

[reynoldston]

you keep saying its a old mower just how old? if that is so it will have ignition points and condenser. They would be under the flywheel and if so either clean and re gap the points or replace them.

 

[EngineMan]

you keep saying its a old mower just how old? if that is so it will have ignition points and condenser. They would be under the flywheel and if so either clean and re gap the points or replace them.

There are no points and condenser on this one....! going by the model number.

 

[Fish]

We have a huge wave of folks with "no spark", but I am guessing that they are not correctly testing for "spark"......

Holding in your hand is no way to test..........

 

[ILENGINE]

We have a huge wave of folks with "no spark", but I am guessing that they are not correctly testing for "spark"......

Holding in your hand is no way to test..........

But its fun to watch people dance around after somebody cranks the engine, and they have good spark.

Years ago owned a wisconsin 7 hp engine with the old style magneto ignition. You could turn the flywheel by hand and it would click when it energized the mag and sparked. My brother wrapped the starter rope around the starter pulley, and had me crank the engine slowly. It got him three times before he could let go.