JD 175 backfires when cranking

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 .

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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????).