I have a 6.5hp briggs on a poulan pro mower. The coil will spark a few times and quit, spark and quit.

[Scrubcadet10]

I think he means he had purchased a new coil for another machine, that works on it. but not on his problem engine.

 

[moodymac]

Both.

No, the machine which worked perfect was working on the parts (coil and plug) which tested bad on the above machine. When tried on this machine, it had no spark and of course would not start. Something is causing the coil to miss-fire. I ran down the ground kill switch, tested the ground wire, and disconnected the ground wire at the coil, and it still would only make intermediate sparks. Just to make sure I was not dealing with two bad coils (the original coil and the new one), I tried it on another engine. It showed spark on the tester and the engine started and ran. I still do not know what is causing the coil to miss-fire on the engine in question.

 

[moodymac]

I think he means he had purchased a new coil for another machine, that works on it. but not on his problem engine.

When you say “works perfect”, does that mean problem solved?

No, the machine which worked perfect was working on the parts (coil and plug) which tested bad on the above machine. When tried on this machine, it had no spark and of course would not start. Something is causing the coil to miss-fire. I ran down the ground kill switch, tested the ground wire, and disconnected the ground wire at the coil, and it still would only make intermediate sparks. Just to make sure I was not dealing with two bad coils (the original coil and the new one), I tried it on another engine. It showed spark on the tester and the engine started and ran. I still do not know what is causing the coil to miss-fire on the engine in question.

 

[moodymac]

I think he means he had purchased a new coil for another machine, that works on it. but not on his problem engine.

Correct.

 

[moodymac]

When you say “works perfect”, does that mean problem solved?

No, the machine which worked perfect was working on the parts (coil and plug) which tested bad on the above machine. When tried on this machine, it had no spark and of course would not start. Something is causing the coil to miss-fire. I ran down the ground kill switch, tested the ground wire, and disconnected the ground wire at the coil, and it still would only make intermediate sparks. Just to make sure I was not dealing with two bad coils (the original coil and the new one), I tried it on another engine. It showed spark on the tester and the engine started and ran. I still do not know what is causing the coil to miss-fire on the engine in question.

 

[artemjemmy]

I’d set the armature air gap to .008 and see if there is any change. Very seldom do magnets go bad. Finally, checking resistance on today’s coils is meaningless, as they contain Hall effect triggers which you need high tech equipment to check.

There are a huge variety of different methods for creating spark on small engines. Briggs uses the magetron setup with a trigger coil and a darlington transistor, tecumseh used a basic CDI method, and others like stihl have microprocessors in their magentos to limit top-end RPM. There was also the kohler DSAI modules, and the kohler SAM system, (both of which were so bad that kohler discontinued them). This sort of stuff is very interesting to me and I want to know more about the circuitry in these modules, but removing the epoxy is very difficult.

 

[moodymac]

There are a huge variety of different methods for creating spark on small engines. Briggs uses the magetron setup with a trigger coil and a darlington transistor, tecumseh used a basic CDI method, and others like stihl have microprocessors in their magentos to limit top-end RPM. There was also the kohler DSAI modules, and the kohler SAM system, (both of which were so bad that kohler discontinued them). This sort of stuff is very interesting to me and I want to know more about the circuitry in these modules, but removing the epoxy is very difficult.

Interesting. Where is the Darlington transistor located? Could this be the cause of intermittent spark?

 

[artemjemmy]

Interesting. Where is the Darlington transistor located? Could this be the cause of intermittent spark?

If I recall correctly, the darlington transistor is "turned on" by the magnetron-branded trigger coil, and when the transistor is on, it allows current to build in the primary winding.

 

[moodymac]

If I recall correctly, the darlington transistor is "turned on" by the magnetron-branded trigger coil, and when the transistor is on, it allows current to build in the primary winding.

Yes, I just read up on it. It is located within the coil itself. This could not be my problem due to the fact of the coil not working properly on the problem machine, yet working just fine on another. My guess right now is it has to be the flywheel. Somehow it is capable of sending enough magnetic force causing a spark for just a few revolutions of the wheel. When the flywheel comes to rest, it regains this energy. If I had another flywheel on hand, I would test this theory.

 

[Scrubcadet10]

Yes, I just read up on it. It is located within the coil itself. This could not be my problem due to the fact of the coil not working properly on the problem machine, yet working just fine on another. My guess right now is it has to be the flywheel. Somehow it is capable of sending enough magnetic force causing a spark for just a few revolutions of the wheel. When the flywheel comes to rest, it regains this energy. If I had another flywheel on hand, I would test this theory.

could you swap over the flywheel from the other machine? it can take some effort if you need a puller, but it may be worth a shot?