Firing problem

[jerkputter123]

I am helping a friend who lives too far for me to drive. He has a Scag zero turn mower with Kohler Command PRO CV740 . He bought the coil change over from NAPA because one of his coils burned up. He has wire brushed under where these modules fits. Set the air gap to .010 . Cleaned the flywheel and double checked the magnet. With the kill switch wire not even connected it still won't fire he tells me. What has he missed. ? I know these coils are old school not needing power to make them fire. He said his ground was good but I did tell him to double check that good. Any thoughts ?

[KE4AVB]

Don't know what he means by burned up. But with Kohler twin coils the internal diode can short out. The coil with the shorted diode actually can still be firing but will cause the other coil to not fire.

Have your friend to remove both kill wires and try starting the engine but have him prepared to either choke the engine to death or remove the fuel source in order to kill the engine. Sometime all it take is the anti fire solenoid voltage to be removed. IF the engine starts and runs normally then he has a second coil failure. The last time this happen here Kohler had me to replace both coils but of that engine was under so-called warranty; although, local dealers refused to honor Kohler's word.

An alternate solution could be to make up a Briggs style v-twin diode harness.

[jerkputter123]

It melted the top part of the coil so he just bought the updated coils which need no volts to fire them. Just 2 modules and kill switch wires. He tried it without the kill wire connected. Air gap set correct and still no fire. I will know tomorrow after he rechecks the ground tonight.

[KE4AVB]

The kill wire needs to be disconnected at both coils but a new install of both it should had fired; unless, he connected the 12V lead to the coils. Have him check the flywheel magnet strength.

[jerkputter123]

The kill wire needs to be disconnected at both coils but a new install of both it should had fired; unless, he connected the 12V lead to the coils. Have him check the flywheel magnet strength.

How would he test the strength of the magnet ? He said he stuck a screwdriver to it and it pulled it in. He has nothing connected to the coils now. I will ask him about connecting 12 volts by mistake but I don't think he did.
This is what he used.
Genuine Kohler Mdi Module Conversion Kit, 25 707 03-S

[hanz63]

It sounds to me like it was suggested that these new coils got voltage sent through them. Maybe that is what killed his old coil as well. Once they get hit with voltage, the CD is toast. If he removed SAM when he installed this kit, you redo the harness.

[jerkputter123]

It sounds to me like it was suggested that these new coils got voltage sent through them. Maybe that is what killed his old coil as well. Once they get hit with voltage, the CD is toast. If he removed SAM when he installed this kit, you redo the harness.

I talked to him today and he didn't connect power to them. This person is very sharp and has owned his own garage business for 35 years. He just don't work on small engines and this one threw him a curve when it was supposed to be a simple change over. He didn't get a chance to work on it last night. It belongs to his son in law. I think it was overcharging and damaged the coils. He did say there was a ground wire loose. I will let everyone know what he finds.

[KE4AVB]

The automobile industry and the small engine industry technology are quite different are at times. So it is not as easy to switch between the two without some knowledge of both. It is just like having a good working knowledge of four cycle engines and then trying to apply that same knowledge to two cycle engines. Some things are the same and others are completely different. It gets a lot of mower mechanics in trouble when they first start trying to repair two cycle handhelds.

It is also possible that he has gotten a previously installed set of coils that were return and just put back in inventory without them being checked. I have rejected electrical components in the past because of installation marks when they were supposedly new items.

If he have install them per the included instructions he should be contacting the his supplier (Napa) about getting a replacement set as even if the coils are installed upside down they would still have produce a spark as long the no kill was ever attached. Note some vendors flat refuse to accept electrical returns; unless, replacement are sent. Even then they are leery at times about doing it. This is where having a good working relationship with your vendors is important.