Export thread

I think I have read every post on every small engine forum in cyberspace about this problem. Motor is a Kawa FC420V 14hp single cylinder with 120psi compression, new coil, new igniter, rebuilt carb, new fuel pump and fuel lines, new fuel cap, new alcohol free fuel, and new flywheel key in slot as it is supposed to be. The coil was gapped on the flywheel magnet per specs and the valves were set to spec at TDC. It cranks fine and fires when choke valve is closed, but when I pull the lever back to Mr. Rabbit or Mr. Turtle it goes putt putt putt with a little smoke out the muffler, then KERPOW!! Upon examination, the spark plug is dry, but covered with black soot.

I don't think its getting too much gas, just gas at the wrong time or place. I've done everything I think possible to get the timing right, and I wouldn't expect a burned exhaust valve with 120 compression.

If I find the problem before I'm institutionalized, I'm sure it will be some minor detail that is staring me in the face that any novice 10 yr. old technician would see. All suggestions are welcome.

sit back, relax and listen to my voice ( as you imagine it ).
now you are getting sleepy, sleeepy. sleeeepy.
You are going back in time , back in time , way back in time to a happy time when your mower worked fine.
Now what started to happen to make you want to fund the parts man's retirement .

bertsmobile1 said:

sit back, relax and listen to my voice ( as you imagine it ).
now you are getting sleepy, sleeepy. sleeeepy.
You are going back in time , back in time , way back in time to a happy time when your mower worked fine.
Now what started to happen to make you want to fund the parts man's retirement .

Click to expand...

Too late. I replaced everything except the cup holder and it runs great. Now if my beer would quit tipping over.:confused2:

What was the problem? Sounds really rich to me.

Gatafly said:

What was the problem? Sounds really rich to me.

Click to expand...

I figure he forgot to put his beer in the "Beer-Holder" ........ :laughing:..:laughing:

Normally, I would agree with the rich diagnosis, but this carb only has a low speed mixer and it is out only one turn and plug is dry after cranking. I rechecked the valves and set them at .006. I think they were a bit loose. Now, it won't fire at all. EVEN after a couple teaspoons of gas down the throat, and yes there is a strong spark all the way to the plug gap.

I've not been able to look at it for a few days, but am going to stick an endoscope in the combustion chamber before I pull the head. I fully expect to see some kind of a fat gremlin in there sitting on my intake valve.

Final remedy? I have the identical problem and have thrown every conceivable part/diagnosis at it with no resolution. Tried new JD coil and trigger, new plug. Swapped good used carb, coil, trigger, flywheel, ignition switch. Valve job and reset valves...many times. Removed engine and sump and visually checked internals. Tried day gravity-feed gas tank with new fuel. Obviously checked flywheel key and grounded/ungrounded ignition/coil/trigger connections. On a JD LX176......FC420V-AS10......FC420VA07172. Still backfires when trying to start and I’m beyond stumped!

Oh yeah.....forgot I did leakdown and compression test. Minimal leakage through carb/exhaust/rings and 67 psi with compression release. Good spark but apparently not at the right time although the valve openings/closings look okay. Grrrrr"...

Check the flywheel key

Checked the flywheel key on the original flywheel, when the good used flywheel was tried and again when the original flywheel was reinstalled.....all looked fine.....even unplugged the stator since somebody on another forum said they corrected their problem by doing that (although I still don’t see how????).

Do you know if this engine was rebuilt or torn into ?

Nothing tells me the engine was rebuilt although it’s a customers so who knows. Another mower shop verified the coil and trigger numbers purchased from Deere since that was the original diagnosis. A true puzzler.....the shop owner can’t figure it out and he’s about as sharp as they come. I’m just a donkey to roll thoughts off of and contribute what I can. I have a good running LX172 with the same engine that I’ve been “borrowing” parts off of to try.

I am wondering about either the engine has been opened up and the camshaft isn't properly timed or even more remote that the gear has slipped on the shaft for some reason.

A local JD dealer suggested that the intake valve seat came out so we took the head off again and rechecked the valve job we had done....no loose seat and both valves looked good. Then we removed the engine and took off the sump, the cam timing marks were aligned but we wondered if possibly the cam shaft became twisted somehow.....kinda far-fetched but more in line with your thinking that the valves are out of time. We didn’t remove the camshaft but simply buttoned it back up because everything looked good. Cam lobes look good based on the observed lift of the rockers and the valve lifter rods are straight. Tried different combinations of new JD parts and good used parts from my running engine...all to no avail so far.

if I remember correctly, the cam gear is keyed onto the camshaft and we checked for the key to be sheared but it was intact. Quite the challenge.

Do you think you could make a video of it backfiring?

If it is backfiring out the carb then either the timing is too far advanced or the inlet is not closing properly

Definitely backfiring out the carb....tried another carb and another fuel supply (day tank) with same results. Video is a possibility....shop owner is more tech savvy than me. Supposed to be getting another small engine mechanic visiting today for another opinion...we’ll see what he has to say.
Watched the valves working with the cover off thinking maybe they were “hanging up” intermittently even though we did a valve job....nothing jumped out at us. Thinking of replacing the engine since the owner is getting impatient and then tearing down the old one for a complete “autopsy” at our leisure. It’s us against the Kawasaki gods now!!! Economics went out the door twenty hours ago when the initial coil and trigger replacement didn’t solve the problem.

You did check the valve guides when did the valve job? Worn guide can cause a valve to hang partially open at times. Random miss fire can also be by a leaky intake manifold. I had a Briggs last year that randomly backfired (sneezed) through the carburetor because of a bad o-ring gasket, nearly kill the engine at times. Just a thought.

I didn’t do the valve job but saw the aftermath after re-removing the head. We removed the intake valve entirely, checked the lapping surface and reassembled....nothing of note. The gasket for the intake at the carb is oversized and not brand new but appeared to be sealing. I had to remove the gasket from the original carb (where it was stuck on) and use it on my carb when checking for an overloading gas supply due to a faulty needle valve/carb. Again, the intake gasket is not new but not torn.
Gotta thank all you guys for the info and suggestions.....nice to have folks take time to try to help others.

Just an addition..The engine does not start and the backfire is not an explosion but a muffled pop with occasional small flame burst visible in the carb throat. I’m stuck on a timing issue. Grasping at straws, the Muffler doesn’t seem blocked and the valve reed that vents into the valve cover seems okay.

Update. We purchased a good used engine (Fc420v-cs00) and installed it to basically get the John Deere mower out the door and back to the customer. With Spring around the corner and the pressure to repair the mower off, the problem with the “old” engine may take a back seat to more pressing matters although I sure would like to know what’s wrong with the engine. Just for information, we switched the muffler, oil filter system and carb between the two engines to make them compatible and for improvement.

Has to be a timing problem I'd think. Is it possible to put the coil on upside down?

I don't think so if it has the original plug lead on it but anything possible. Have tried a different Ignitor? I know try can fail strangely.

I tried putting the brand new coil on upside down with no difference.....the spark plug wire had to be rerouted but reached the plug.....the kill wire had to be jumped to reach. Also tried a good used coil and trigger by themselves and in all combos with the newly purchased OEM ones. I’ve marked where the intake and exhaust valve opens and closes on the flywheel and where the decompressor blimps.....all on the engine that doesn’t start. Next I want to mark the same thing on the good used engine once I get all the “donor” parts back on....then compare the marks. Too cold to mess around too much here at home.....27* high with no garage heat!

Now you know why I not working on the Farmall Super M this week. All I like is the left brake assembly remounting. Just too cold with the wind chill and the snow flurries.