Briggs & Stratton will not fire unless I do This....

garybryan · Apr 1, 2016

Hello Everyone,

I am in a bit of a bind and need some help!

I have a 19.5 HP twin cylinder model#4617047 Briggs & Stratton in a Craftsman LT1000 riding mower.

I have no spark, I checked the kill wire and all related switches. I removed the kill wire from the coil, I think that eliminates all safety switches. I have checked the coil contact points, they are clean and the coil is tight. I checked and rechecked the coil clearance to the fly wheel. I replaced the coil.

I removed the boot from one of the spark plug wires and plugged the wire back onto the plug, if I place a screw driver on top of the spark plug wire while it's still plugged to the spark plug and ground the other end the engine will fire and stay running
until I remove the ground. HELP

I thought the engine might be missing a good ground, although it cranks over fine, so I used a jumper cable to run a ground directly to the engine block, the head and no go.

Thanks in advance for all your help.

ILENGINE · Apr 1, 2016

will the engine run with just one wire connected to the spark plug, and the other one unplugged. Was that a new coil that you installed. This sounds like short in the secondary winding of the module. Faulty ignition module would be the cause if this what is happening.

garybryan · Apr 1, 2016

ILENGINE said:
will the engine run with just one wire connected to the spark plug, and the other one unplugged. Was that a new coil that you installed. This sounds like short in the secondary winding of the module. Faulty ignition module would be the cause if this what is happening.

The engine will run with one wire disconnected as long as either (disconnected one or plugged one) wire is grounded.

It had the same problem with the original coil, and yes, I fitted a new coil. Same problem.

BlazNT · Apr 2, 2016

Picture of the coil mounted to mower if you would.

Tinkerer200 · Apr 2, 2016

I don't think you answered if the replacement coil was new. Your symptoms are of a faulty coil.

Walt Conner

garybryan · Apr 2, 2016

Re: Briggs & Stratton will not fire unless I do This....FIXED!!!

Thank you to all that answered my post. I figured it out!! I will post the solution so that anyone finding themselves in the the same
situation has an easier time than I getting their machine running.

When I installed the new coil I made sure to clean the mounting points of coil, to clean the magnet and to properly adjust the gap between the module and the magnet. What I didn't do
is clean the rest of the fly wheel surface. Apparently, the magnet plays a part and the rest of the wheel,which is grounded plays another. In this case enough light rust build up to
prevent the module to work properly.

Tinkerer200 · Apr 2, 2016

I doubt that seriously. Rust or dirt on coil laments or flywheel will not build up enough to affect magnetic flux. Your cleaning was co-incidental to whatever you did resulting in the coil working.

Walt Conner

BlazNT · Apr 2, 2016

Rust will stop ground to engine block if under coil where it connects to block. At least that is how I read the post.

Tinkerer200 · Apr 2, 2016

BlazNT said:
Rust will stop ground to engine block if under coil where it connects to block. At least that is how I read the post.

That is not what we are talking about and not what the OP said cured his problem. He said he did what you are referring to and did not cure the problem. Then he cleaned the laments and the none magnet part of the flywheel and did cure problem.

"When I installed the new coil I made sure to clean the mounting points of coil,"

"What I didn't do is clean the rest of the fly wheel surface. Apparently, the magnet plays a part and the rest of the wheel,which is grounded plays another. In this case enough light rust build up to prevent the module to work properly."

Walt Conner

bertsmobile1 · Apr 2, 2016

A common missconception.
The magnet grabs on the scrap yard machines had rust an inch thick on them more often than not.
Rust does not affect the flux unless it is fine powdered and there in sufficent volume to complete the flux lines and short out the field.
On the flywheel magnets you would need about 2Kg of rust dust, iron filings etc.
So no cleaning the flywheel magnet or the coil laminatons do absolutely nothing.
If it was a problem they would be painted from new.
The coil and thus the module earths out at 4 points. Under the head of both mounting bolts and between the laminations and mounting plinths.

The only time cleaning makes a difference is if the rust actually bridges the gap and thus build up heat from frictional contact.
I will hazard a guess that near one of the mouning bolts there was a piece of wire that made the earth connection which is now making contact.

Briggs & Stratton will not fire unless I do This....

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