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"Megafire" ignition issue


PhanDad

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The "Megafire" ignition module installed on my T-12 12HP Briggs gave me some trouble tonight while mowing (hot here today).

Engine ran fine for about 1/2 to 3/4 hr.  Then when I increased the throttle, the engine quit, ran, back fired and blew the welch plug out.  I was low on fuel, so at first I thought that was the issue as I was going uphill on a side slope which has caused fuel issues before.  However a short while after refueling, I lost spark again (no backfire).  Checked all wiring connections and tightened them up.  Started mowing again and when I increased the throttle setting, the quit, ran, backfire, welch plug ejection.  After reinstalling the plug, I finished mowing at about 3/4 throttle without issue.  

Bach in the shed, without mower load I was able to go full throttle (no mower deck load) without issue.  So I'm thinking the issue was heat and a breakdown of some insulator in the module.  Or maybe a heat issue.

Anyone have this issue?  

All thoughts welcome.

I do have spare modules so I'll probably install a fresh one before I mow again.  

 

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13 hours ago, Chris727 said:

Could the coil itself be starting to fail?

Could be I guess.  I think I've only replaced it once in the 50 years of it's life.  

 

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On 7/5/2023 at 10:44 PM, PhanDad said:

The "Megafire" ignition module installed on my T-12 12HP Briggs gave me some trouble tonight while mowing (hot here today).

Engine ran fine for about 1/2 to 3/4 hr.  Then when I increased the throttle, the engine quit, ran, back fired and blew the welch plug out.  I was low on fuel, so at first I thought that was the issue as I was going uphill on a side slope which has caused fuel issues before.  However a short while after refueling, I lost spark again (no backfire).  Checked all wiring connections and tightened them up.  Started mowing again and when I increased the throttle setting, the quit, ran, backfire, welch plug ejection.  After reinstalling the plug, I finished mowing at about 3/4 throttle without issue.  

Bach in the shed, without mower load I was able to go full throttle (no mower deck load) without issue.  So I'm thinking the issue was heat and a breakdown of some insulator in the module.  Or maybe a heat issue.

Anyone have this issue?  

All thoughts welcome.

I do have spare modules so I'll probably install a fresh one before I mow again.  

 

Sight unseen we all know it could be a few things. My suggestion is maybe a blocked fuel vent in cap. This recently happened to me in the way you describe, so I  swapped out the suspect cap/gauge with another and cut 5 acres without a hiccup. I never run those modules as they are not as good as the original equipment. The original Briggs is bulletproof. One of mine with a 16 HP  has been running (best I believe) since 73  with proper maintenance is still a strong runner. Back when  a Briggs was a Briggs.

Hope this helps

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If I had to pitch out a guess, first  I would say partially sheared flywheel key...   Easy to check off the list , as problems would be all the time. Would not come and go.

 

If not that, second guess would be a failing factory coil...   Problems would come and go with heat. Try another module and see if it still happens.

 

Third guess would be heat issue with the module...  Same advice as guess #2, try another module and see what happens.

 

 

Just guesses based on previous experience....but guesses none the less. Value accordingly...use at your own risk9_9

Edited by SmilinSam
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Chasing the same thing with an Onan now. Ruled out failing key switch today as far as intermittent spark. Coil & condenser are next. Followed by ignition module, rotor & or key in the end if needed.

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On 7/8/2023 at 5:00 PM, Austin said:

Let us know what you end up doing.

Module is a NOVA II; swapped it out for another NOS NOVA II I had on hand before I mowed today.  

The tractor started almost immediately (an improvement) and no issues at high throttle and a fairly hot day.  

So.... I'm thinking heat has affected it just as heat sometimes affects the Interlock Module on newer Sovereigns.  The module was installed in July 2012, so it doesn't owe me anything.  

Hopefully I won't have anything further to report for another 11 years.  

 

Edited by PhanDad
Added "NOS"; "had on hand"
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  • 1 month later...

Also make real sure you have good fuel, good flow,  and that the fuel filter is good. Fair to mention I had water in the fuel before that did the same thing as yours.

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