Weird Magnum Ignition issue??

[Docwheelhorse 2,660]

Hello all,

Have a problem thst I'm trying to troubleshoot.

12 hp Magnum... generally starts easy and runs fine.

 

Depending on weather conditions (damp and cold seem to cause issue)

 

It either won't start and as it cranks you can hear it popping back thru carb / hear what sounds like flame blowing back into air filter. Like the ignition timing is super advanced or intake valve is hung open. 

 

Leave tractor alone and it will start fine if you go back several hours later.

 

Also---I can get tractor started easy and it will start working and then quit / start doing the above. Again leave it alone and it will eventually start and run fine.

 

So... bad coil? Carb messed up? Ignition switch? Intake valve hanging? What should I go after first? 

 

Thanks Tony

 

 

[Achto 27,571]

Is this a magneto or battery ignition?

[pfrederi 17,739]

All magnums are magneto

 

  Checked air Gap on the coil/Flywheel?????

 

Magnets all in place??

Edited January 19, 2022 by pfrederi

[peter lena 8,627]

@Docwheelhorse  sounds like a corroded  connection to me , related to  , damp cold , my base line help for ignition  , wiring issues , is to , just easily try this , clip on battery cable from battery ground bolt , behind dash to corner of engine / frame  near clutch pedal . then run a  wire from there  to the , rectifier ground mount bolts . move or verify all your plug in wiring , check fuses . if this works , go back and replace every weak point , till it  solidly  runs. worth a try , pete 

[peter lena 8,627]

@pfrederi  have never checked the air gap on my magnums , too much obvious related , wiring / corrosion  was the cause.  another thing in enhancing the rectifier ground area , is that , same point will enhance your headlights for grounding , with added wire , pete

[Pullstart 62,870]

@Docwheelhorse did you ever get this fixed?  My Magnum 10 has started this same thing on occasion.  Once it fires up, all is well.  

[953 nut 55,228]

      Rust on the flywheel could short out the air gap under the right conditions and not do it other times.  

[Rick3478 428]

A bit late to the party, but have you had the cover off?  I just had to replace the coil on one of mine.  Y'know mice can get in there and they love to pack the space with nesting material, acorns, and babies.  And they love to chew on things.  You might think they would be satisfied to just eat the insulation, but there were two inches of copper missing.  So in your case, could be shorting out when damp, dry out and work later.

[JoeB 15]

how do you take the cover off?  i have a similar starter problem on  my 312.  thanks

[Rick3478 428]

43 minutes ago, JoeB said:

how do you take the cover off?  i have a similar starter problem on  my 312.  thanks

It's almost self-evident.  For starters, remove the wingnut and decorative air filter cover, as it is keyed into the cooling shroud.  Next is the choke/throttle bellcrank assembly, which attaches to the shroud with two bolts.  The choke/throttle can be left together hanging in air if you remove its two bolts from the shroud.  Then there are about five bolts around the edge of the shroud holding it to the head and bearing/magneto plate.  Two of them are sort of out of sight on the bottom, one of them probably also mounts a clip that holds choke and throttle cables and fuel line.  After you've removed those, the shroud pulls straight off.  Pay attention to orientation of parts and which bolts came from where, and reverse the process when going back together.  Can probably be done with a small crescent wrench, though I'd recommend at least 3/8" and 7/16" combination wrenches.  Sockets, extension, and t-handle or ratchet optional for speed.  I may have forgotten something, it's been a few months, but that's the gist.

[RED-Z06 2,221]

My m12 started hard, would misfire, backfire...then run fine.  Replaced the coil and its fine..im assuming some crack in the armature that intermittently disrupted the windings