View Full Version : kawasaki fc420v weak spark

05-23-2007, 12:46 AM
This is my first post, although you guys have provided many answers for me in the past in your solutions for other folks' posts. I have a 20 year old john deere lawn tractor with a kawasaki fc420v engine. Lately it has been getting harder to start and now, finally, it won't start at all. I have checked the spark and it is very weak. I checked the coil and it is ok. The ignitor is ok too. The key switch appears to be bad according to the electrical diagnostic in the deere tech manual. The red blue wire that goes to the breaker also failed the test. I bypassed the switch and replaced the wire = still weak spark. I think the starter is going bad from overheating (even though I never cranked it more than 10 seconds before letting it rest) it sometimes gets very hot and begins to slow down. Is it possible that the starter isn't turning the flywheel fast enough to get a good spark? Would a relay kit help? Is the relay kit the parts that include the clutch or the parts that include the brushes?

Thanks for any help in advance.

05-23-2007, 02:28 AM
If you know the starter is getting hot at only a 10 second crank then replace it. Faster cranking will mean better spark and better starting. I'm not sure of this relay kit you speak of. I would just replace the starter. An aftermarket starter should set cost about 125.00 with an OEM about 180.00

05-23-2007, 07:58 AM
From what I've read the relay kit is added to supply more voltage to the starter instead of going through the whole wire harness (less voltage drop to starter).

Replace the switch if it tested bad, Install the relay kit then move to the starter as khouse mentioned. Also make sure your battery is up to par.

05-23-2007, 10:58 AM
Thanks for your suggestions, guys. I am going to get the key switch and check on the relay kit at the John deere dealer. I found a remanufactured starter for 95$ at a starter repair shop, if I need it. One question: Would the repeated cranking of the starter cause the wiring to heat up and damage the key switch and the red blue wire in the harness? I am just wondering what might have caused that...

05-23-2007, 01:09 PM
One question: Would the repeated cranking of the starter cause the wiring to heat up and damage the key switch and the red blue wire in the harness? I am just wondering what might have caused that...

It's very very possible.....

06-02-2007, 08:25 PM
Well, I had the starter rebuilt = it works fine now. I replaced the key switch and I replaced the red/blue wire as well. I still have a weak spark. The electrical system diagnostic says I have an "open" circuit on the yellow wire to the voltage regulator. I checked the entire length of the yellow wire one piece at a time for continuity and it checked fine. The yellow wire supplies current to the pto switch, headlights and panel lights. all of the switches have tested ok; all of the fuses as well... I am baffled. :dizzy: I figure there is a wire grounded somewhere possibly, but in order to check I will have to individually check each wire in the harness - j Deere no longer carries a replacement harness for this model. Is the flywheel possibly the culprit? How would I check it? The magnet seems powerful to me. What is a sheared key? Could that cause a weak spark? Any Ideas would be greatly appreciated!

06-02-2007, 08:41 PM
The Yellow wire you speak of very well could test open until the engine is running because thats the voltage output from the regulator, Thats why it's hooked to the PTO switch.

Sheared flywheel key will not cause weak spark but cause spark to be out of time.

Since you have the cranking problem solved you should test the ignition system components, Procedure below;


06-02-2007, 10:30 PM
Thanks for the quick reply Restrorob. I just checked both the ignitor and the coil and they are in spec. The ignitor started another J deere mower at the dealer last week. The coil is brand new, but iI checked it anyway. Any other ideas? I am stumped!!!

One other thing. I disconnected everything from the voltage regulator and checked for continuity between the red terminal that connects to the battery and each of the other terminals on the v. regulator that have connections. All of them had continuity except the terminal which connects to the yellow wire. In other words, there is no continuity between the red wire terminal and the yellow wire terminal on the voltage regulator. Is this the correct result?

06-02-2007, 10:45 PM
How is the air gap between the coil legs and flywheel?

06-02-2007, 11:13 PM
I checked that several times and even tried readjusting it. The manual says it should be .012. I used my feeler gauge and set it that way. I placed the gauge on the magnet and rotated the flywheel until it reached the coil. I held it tight and tightened the screw. Same for the other contact. I then rechecked them for fit. A friend said to use two pieces of paper for a gauge instead. I tried that gap too. Neither one seemed to make a difference.

06-03-2007, 12:38 AM
If you want to check the charging system here is the proper specs/procedure;


The charging system has nothing to do with the ignition system.

Have you tried a new spark plug ? I have found new plugs bad right out of the box.

Disconnect the black engine kill wire from the unit harness and check for spark again, You could be getting a feedback from a safety switch.

06-03-2007, 09:28 AM
Thanks for the regulator test diagram, Restrorob. I didn't know if the regulator had anything to do with ignition or not - guess I am grasping at straws. I'll try a new plug - this one had been working previously and is relatively new - but you never know. The kill wire is the black one running from the ignitor to the tab on the coil, right? I will try that too. I really appreciate the help. This mower has really given me my money's worth, I just hate to give up on it.

06-03-2007, 09:46 AM
The kill wire is the black one running from the ignitor to the tab on the coil, right?

No, The wire from the igniter to the mower wire harness, The coil and igniter have to be connected together to get any spark at all.

06-03-2007, 08:30 PM
Well, I feel just like that lawnmower mechanic in that movie "Slingblade", where the guy says "ain't got no gas in it, mm hmmm". The spark plug I had in the mower was apparently bad. I bought it in May and it had been working fine up until the mower wouldn't start. (Although it had been getting progressively harder to start.) I never would have expected the spark plug. Why do I always overlook the obvious? Anyway, I do think I had a multilayered problem, and at least I learned something and hopefully headed off future problems - ie the starter. Thanks for all your help guys, especially Restrorob, for being so helpful. Time to mow some grass.:clapping:

06-03-2007, 09:08 PM
Bet I know the first thing your gonna do if it goes to running bad again....:laugh:

Glad to hear ya got it going.