Export thread

Trying to help my 80 year old uncle get his John Deere mower running again.
It has a Kawasaki FC420V engine.
It had a new coil two years ago.
No spark this Spring and we determined the ignitor was bad.
Ordered a new OEM igniter / module.
My uncle installed and he said it ran great for 1/2 hour or
less and he shut it off, and was never able to get it
started again.
It now "pops" in the carburetor and flames are visible in the
carb intake (with air cleaner off).
Spark at plug appears to be good.
New spark plug was tried.
Flywheel key looks good.
It has 118 psi compression, so it can't be an intake valve
"hung up".
Ideas appreciated!
Tom

Google: "K&T Parts House Kawasaki Engine Repair Manuals" , click on FC420V 4 down, download at bottom left of screen, see troubleshooting section page 8.




























Google: Kawasaki mower engine repair manuals, click on " K & T PARTS HOUSE REPAIR MANUALS", click on FC420V 4 down, download at bottom left of screen, see troubleshooting section page 8.

Thanks! Manual downloaded, and will start "looking"!

Went thru the manual last night and nothing really "popped out" at
me regarding what may be the problem with this mower popping
and spitting fire out the carb intake, and not starting.
At $70 a whack for a new igniter / module I hesitate to have
my uncle buy another one just to try it.
I did an ohm test on the original module and got the same readings
when test leads were "swapped", and therefore was determined bad.
New module / igniter has different readings.
My ohm meter is "auto sensing" and isn't coming up with the
spec readings. The manual did mention to use the Kawasaki approved
test meter or you may get the wrong readings :-(
I'd find it hard to believe the valve timing could have jumped.
I'm still open to ideas. Thanks, Tom

Ok so Lets think this through. Gas fires in the cylinder. Fire should only be there. What stops the fire from entering or exiting the cylinder? Valves that are timed correctly so they open and close at the correct time so burning gas does not go into the intake manifold or exhaust manifold when it is not supposed to. So if fire is in the intake manifold either some one has places a spark plug in there or the valve is not closing at the correct time or completely. So what could cause this? Timing off, in correct valve lash. So I would check the valve lash and the shear pin. Not just look at it but remove it and inspect.

If it is truly an electronic module it cannot be trouble shot? The manual tells you how? Next , isn't 118 lbs compression a little low? Taken hot or cold, with carb butterfly open? Just comments. Valve timing doesn't jump , it changes slowly as lash changes. As cam contour turns round it picks up the lifter/valve later due to the increased lash (clearance).

Blaz & Motorman,
Thanks for your replies. I believe the manual said 70 psi was
minimum compression for these engines, if so, I would think
118 would be great. Agreed that it would be hard for gear driven valve timing
to change. I can't picture what could have happened to the valve
lash to cause the intake valve to be open at TDC on compression
stroke and still have good compression.
My uncle was a mechanic a good deal of his 80 years, but I did
question him about the flywheel key, and he said he checked it
and it was "clean as a whistle". Next visit there I'll see if I can
convince him to pull the flywheel so I can see.
I will check the valve lash. It seem to crank over good, so I think
the exhaust lash with the compression release is working okay.
I'm guessing it's the igniter module, but hopefully the flywheel key!
Thanks for your help. Will try to report back if we find the problem!

QUOTE=BlazNT;231676]Ok so Lets think this through. Gas fires in the cylinder. Fire should only be there. What stops the fire from entering or exiting the cylinder? Valves that are timed correctly so they open and close at the correct time so burning gas does not go into the intake manifold or exhaust manifold when it is not supposed to. So if fire is in the intake manifold either some one has places a spark plug in there or the valve is not closing at the correct time or completely. So what could cause this? Timing off, in correct valve lash. So I would check the valve lash and the shear pin. Not just look at it but remove it and inspect.[/QUOTE]

A sticking exhaiust valve can cause blow back out the carb.
Pull off the rocker covers , check the heights of the valves, they all should be the same,
Watch the operation of the valves.
These engines tend to bend pushrods.

Thanks for your reply. I can't visualize how a sticking
exhaust valve can cause blowback thru the carb, but
will check the valve operation anyway.
Thanks!

bertsmobile1 said:

A sticking exhaiust valve can cause blow back out the carb.
Pull off the rocker covers , check the heights of the valves, they all should be the same,
Watch the operation of the valves.
These engines tend to bend pushrods.

Click to expand...

Because when the inlet opens there is still pressure inside the cylinder.

Went to my uncle's today to look at the mower.
Flywheel Key OKAY
Valve lash, ACR, Valve movement, & Pushrods OKAY
Removed the grounding wire going to the igniter module MADE NO DIFFERENCE

Still appears that the ignition timing is way off, and I see nothing that would
control that other than the $70 igniter module that was just replaced.
It seems to be sparking at some point when the intake valve is open.
Looks to have good spark.
Can these modules go bad in this way that the timing could be way off?

I tested the igniter again with my Ohm meter. Two readings are given
in the specs, depending if the Positive or Negative test lead is on
the igniter lead or case.
One reading is in spec, the other is way off. The manual says to set your
meter on 10 K setting. My meter is "auto-sensing". Manual says to use
only recommended Ohm meter, model XXXXX., etc.

Would my meter not be able to read the module correctly?

Curious, What gives the module the signal to do "it's thing"?
Only thing I could fathom would be the flywheel magnets via the
coil.

Just had a thought, could one use an automotive timing light to see
if indeed the module is making spark way off of TDC?
If so, HOW?

Thanks again!

BlazNT said:

Ok so Lets think this through. Gas fires in the cylinder. Fire should only be there. What stops the fire from entering or exiting the cylinder? Valves that are timed correctly so they open and close at the correct time so burning gas does not go into the intake manifold or exhaust manifold when it is not supposed to. So if fire is in the intake manifold either some one has places a spark plug in there or the valve is not closing at the correct time or completely. So what could cause this? Timing off, in correct valve lash. So I would check the valve lash and the shear pin. Not just look at it but remove it and inspect.

Click to expand...

tom, since I do not own J Deere and ignition with "igniter" I'm kind of winging it here. The resistance readings may simply be to evaluate the hi volt leads which may have resistor line for elect noise suppression (your neighbor can still see his TV pic). I'm guessing the module is a transistorized circuit where transistor{s) replace the old style point breaker system with rubbing block riding on distributor shaft. If so then something like this...as the magnet on the flywheel passes it induces energy in a coil inside the module and this voltage is processed to the transistor which acts like a switch. It is off and then on, off and then on. etc. The transistor switches the separate wound coil and voltage is produced which we are familiar with as plug voltage. So the timing is mostly provided by the static setting of the magnet vis a vis the coil pick up, and that is phased with the piston and valves. Timing advance in 2 strokes mainly

Other style modules dispense with the coils and use just transistors (Darlington pair is what Briggs uses) which are amplifiers like you have in a stereo, or can use capacitor charge and discharge. These style are semiconductor or "sold state" units. Inside things happen in micro seconds (millionths of one second).

When the semiconductors get over heated they fail , but will still put out erratically at cold, and typically fail altogether at hot. I guess if voltage breakdown occurs it can cause (timing) misfire visible at the plug, and will probably be weak. Yes, I have used an auto strobe timing lite to see my Craftsman Intek output at cranking speed. Because that spark is relatively weak it would barely fire the ?xenon? tube strobe (clamp on style) and I had to darken the garage. The timing pulse was a faint orange-red instead of the white we are use to. If you really want to see the timing you will have to put a ref mark on the engine at TDC and watch the light. These modules may require a minimum (starter) cranking speed in order to produce even the weak, red, strobe . Buying genuine factory parts is a good idea as asia produces millions of semiconductors, most not "screened" for temp or even turned on before shipment so the customer experiences "infant mortality." But in this forum we have reports of brand name "lot failures" of ignition modules. More than you needed.:laughing:

Curious, What gives the module the signal to do "it's thing"?
Only thing I could fathom would be the flywheel magnets via the
coil.

Just had a thought, could one use an automotive timing light to see
if indeed the module is making spark way off of TDC?
If so, HOW?

Click to expand...

The voltage generated by the coil starts from 0 V then rises to around 200 V then drops back off to 0 V
The module reads the rising voltage being generated by the coil and when it gets to a predetermined level it diverts to an earth circuit and send the voltage down the wire to the primary windings.

You can use an inductive timing light to check the timing fairly easily.
Remove the engine cover and spark plug.
with the piston at TDC pop a dot of white paint on the top of a ringear tooth and another spot on the engine case opposite it.
With the timing lamp connected to an external battery start the engine and read where the dot is when the engine is running.
You can count the teeth between the dot on the tooth and the dot on the cases to convert this to cankcase degrees.
Limit this to 10 minutes max as running without the cover will overheat the engine.

To check the stability, once you have established where the dot will be at running speeds, put another mark , a line for instance at this spot.
the rin the engine a second time checking for the dot dancing around the line.
If you want to be really accurate you can stick some wide masking tape on the crank case and mark it out in 2 deg steps from TDC to 20 deg before TDC and paint the while top of the tooth so you are looking at an arrow head and not a dot

Thanks Motoman and Bert for the "high voltage" lessons :laughing:

The replacement igniter was OEM. My uncle told me to go ahead
and order another OEM igniter to try.
Next time at my uncles, I'll throw my timing light
on for kicks and see what happens. Not sure if there's any
specs on those engines for degrees before TDC running,
or if any advance is built in to these igniter modules.
If it would start, I wouldn't even worry about the timing
but thought it might be another diagnostic tool I haven't used yet!
I like working on old outboards....... with points and condensers, lol.
Tom

bertsmobile1 said:

The voltage generated by the coil starts from 0 V then rises to around 200 V then drops back off to 0 V
The module reads the rising voltage being generated by the coil and when it gets to a predetermined level it diverts to an earth circuit and send the voltage down the wire to the primary windings.

You can use an inductive timing light to check the timing fairly easily.
Remove the engine cover and spark plug.
with the piston at TDC pop a dot of white paint on the top of a ringear tooth and another spot on the engine case opposite it.
With the timing lamp connected to an external battery start the engine and read where the dot is when the engine is running.
You can count the teeth between the dot on the tooth and the dot on the cases to convert this to cankcase degrees.
Limit this to 10 minutes max as running without the cover will overheat the engine.

To check the stability, once you have established where the dot will be at running speeds, put another mark , a line for instance at this spot.
the rin the engine a second time checking for the dot dancing around the line.
If you want to be really accurate you can stick some wide masking tape on the crank case and mark it out in 2 deg steps from TDC to 20 deg before TDC and paint the while top of the tooth so you are looking at an arrow head and not a dot

Click to expand...

The new igniter arrived today, so I went to my uncles.
I checked the ohms on the new igniter against the
slightly older igniter. They basically tested out the same
on the meter.
I guesstimated where TDC of the piston was and made
a chalk mark on the flywheel, which basically when the
flywheel magnet is lined up with the coil shoes.
Cranked the engine over with a timing light attached,
first with the older chip, then the newest. The older chip / igniter
seemed to fire the plug a little more advanced than the newer,
but the newer chip fired the plug when the magnet was centered
with the coil shoes.
Tried starting mower with new igniter, and "no go". It's still
creating flames in the carb intake and not really sounding like
it wants to start at all.
We're totally baffled. Surely someone has had this same thing
happen before? :confused2:
Thanks for any more ideas!

tomfg said:

Thanks Motoman and Bert for the "high voltage" lessons :laughing:

The replacement igniter was OEM. My uncle told me to go ahead
and order another OEM igniter to try.
Next time at my uncles, I'll throw my timing light
on for kicks and see what happens. Not sure if there's any
specs on those engines for degrees before TDC running,
or if any advance is built in to these igniter modules.
If it would start, I wouldn't even worry about the timing
but thought it might be another diagnostic tool I haven't used yet!
I like working on old outboards....... with points and condensers, lol.
Tom

Click to expand...

tomfg said:

The new igniter arrived today, so I went to my uncles.
I checked the ohms on the new igniter against the
slightly older igniter. They basically tested out the same
on the meter.
I guesstimated where TDC of the piston was and made
a chalk mark on the flywheel, which basically when the
flywheel magnet is lined up with the coil shoes.
Cranked the engine over with a timing light attached,
first with the older chip, then the newest. The older chip / igniter
seemed to fire the plug a little more advanced than the newer,
but the newer chip fired the plug when the magnet was centered
with the coil shoes.
Tried starting mower with new igniter, and "no go". It's still
creating flames in the carb intake and not really sounding like
it wants to start at all.
We're totally baffled. Surely someone has had this same thing
happen before? :confused2:
Thanks for any more ideas!

Click to expand...

Did you ever figure out what was wrong with the motor? I'm experiencing the same thing. I very much don't want to toss parts at it.. I'm experiencing the same behavior you were seeing.

draker said:

Did you ever figure out what was wrong with the motor? I'm experiencing the same thing. I very much don't want to toss parts at it.. I'm experiencing the same behavior you were seeing.

Click to expand...

Well his first problem was to continue to use his cheap multimeter.
A cheap meter can destroy the chips.
What you have to wrap your head around is you can not speed up electricity
And on a mower engine, the flywheel magnet & coil position is fixed.
So mower engines can not "Advance " the spark.
With the various "Advance " modules what is really happening is the spark is always generated in the full advanced position and the electronics simply delays the timing.
So full advance = less delay.
When a module fails it either fails to open circuit = no spark
or to full advance ( no delay ) backfires through the carb.

However a sheard timing key will also cause a carb backfire
As will an inlet valve that does not close full or an exhaust valve that does not open fully.

The mechanical bits are always easier to check so start with the key.
The flywheel & crankshaft have 1/2 the keyway in each so must make a perfect square when viewed from the end.
Next remove the rocker covers and verify the valve lash and then the opening & closing of each valve.
There should be a small overlap near tdc exhaust stroke.

I wanted to update this thread to mention I fixed my issue by correctly setting the coil gap to .3mm

After that it started right up, no more backfires.