Bit stuck, too lazy to research.

[mindymogul]

So just pulled a 90s B&S 5hp off a old Snapper rotatiller I was gonna use for a kart build. It was running, I took it off now it isn't. The coil seemed in poor condition so I got a new one and plug. What really gets me if the old coil is put on another engine it'll fire but the brand new coil won't fire on this one. So either something's really messed up or this thing is possessed...

Any suggestions?

 

[Nosandwich]

Same spark plug? Stripped cam?

 

[Kartorbust]

Is it possible the gap between the coil and flywheel became out of spec and caused the issue?

 

[mindymogul]

I gapped it to .010 and still nothing. Half thinking the magnet was demagnetized somehow and isn't producing any flux. Granted the new local HF is literally 500ft from me so kinda half tempted to get a Predator but I wanna actually build a 5hp Kart like the good ol days. B&S Model #136200

 

[bob58o]

I just read the other day how to test the magnet on a Briggs.
I do enough research for the lot of us. LOL

http://www.briggsandstratton.com/lam/es/support/faqs/ignition-system-theory-and-testing
Flywheel:
The flywheel magnet must generate a sufficient magnetic field to start the chain of events in motion. A fair test is to hold the flywheel on edge with the magnet facing up. Place the blade of a 10" #3 (1/4") straight blade screwdriver against the magnet. Release the screwdriver. The magnet should have enough strength to hold the screwdriver straight out. If we pass this test, assume the magnet is OK.

 

[Joe-405]

I bet the kill switch wire jiggled loose possibly behind the flywheel.

 

[mindymogul]

Bob had the right idea. It barely held a micro screwdriver hanging. I pulled the coil farthest from the flywheel as possible (3mm) and it has decent spark but the timing is WAY off. If it gets any closer the flux weakens drastically and then no signal gets to the plug. In all my years of working on engines Auto and Small I've never seen anything like this. Going by physics doesn't magnetic flux deteriorate exponentially over distance?

 

[bob58o]

When I read that service notice, I tried on my flywheel. First time I tried the magnet was at 3 o'clock (or 9 o'clock) and the screwdriver fell. Then I reread it and tried with the magnet at 12 o'clock and it held it straight out. It it can't hold a little screwdriver with the magnet at 12 o'clock, then that is probably it.

I was going to suggest checking the flywheel key, but that would only affect the timing - not the spark itself.

 

[mindymogul]

Yep. Another engine for the scrap pile. Picked this up for $15 and found out why it don't exactly run right. This is why I really, really don't like Briggs. AT least Tecumseh carbs aren't nearly as screwed up as this. Predator 212 it is!