Won't start while hot after tilting...

[imagineer]

I have a Scag 52” hydro walk-behind mower with a 16hp Kawasaki FS600V engine. Been using this mower since ’22. It usually starts 1st pull.

After mowing the yard (2.25 acres, about 2 hours), I like to scrape out the cutting deck. To facilitate access to the underside of the cutting deck, I lift the front of the mower and prop it up with a 2’ brace. After scraping out the deck (maybe 5 minutes) and lowering the mower, it won’t start (it’s a pull start). I can pull on the rope until I'm exhausted and it won't start. If I let it sit for 30 minutes or so to cool off, it will start.

Is it possible that because the mower is hot while I’m scraping out the deck, the fuel in the float bowl has boiled off, preventing the mower from re-starting.

If this is the issue, would a carburetor spacer help insulate the carb from the engine heat?

For reference, after the last mowing, I shut it off, but left it level (didn't tilt up the front). 5 minutes later, it did start, albeit reluctantly, on the 2nd pull. When it did start, it coughed out a bit of black smoke.

My previous mower, used from ’99 to late ’21 was a Snapper 52” belt drive walk-behind with a B&S Vangard V-twin; and never gave me trouble re-starting after tilting or when hot.

 

[txmowman]

I highly doubt it is a heat issue with the fuel or carburetor. If it is believed so, why not try to let it cool down before raising it up? Is there any presence of fuel getting in the oil? It really sounds more like a ignition coil issue. The engine is hotter after 5 minutes shut down than it was while running. You are using the choke on restart, correct?

 

[imagineer]

Letting it cool before scraping out the deck isn't convenient. Typically, I'm mowing late evening and am racing the clock to finish before dark. It works out best to wrap up the mowing, drive the mower to my designated scrape out spot, lift it up and clean out the deck. After scraping out the deck, I (try to) start it, run it to the storage shed and park it. I usually leave the shed doors open for a while, but later, close them.

I don't think there is gas in the oil, but I've not owned it long enough to confirm (only changed the oil once so far).
When the mower is cold, I always use the choke, but when it's warm weather, I don't seem to need the choke.
I've not tried using the choke on a hot restart, but weather permitting, I should be able to test that out this Wednesday.

 

[txmowman]

My bet is that the choke will help.

 

[imagineer]

Nope, using the choke didn't help The mower did start, without the choke, again reluctantly, but on the 4th pull, and again, it coughed out a bit of black smoke. All this points to the carburetor leaking fuel into the intake manifold while the mower is tilted up.

 

[StarTech]

Could be a combination problem. Fuel leakage is a possiblity as is a failing ignition coil that getting heat soaked when the engine is hot.

 

[slomo]

Why not dump the oil and fuel out PRIOR to tilting? We all know it could use an oil change anyway. Gas is cheap, $3.80 a gallon thanks to the Biden Cartel.

 

[imagineer]

FWIW, it is looking like a coil issue.

Yesterday, I repeated the same steps that usually cause the mower to not start, and (big surprise) it wouldn't start. I pulled both spark plugs, one was dirty and the other was fine, neither were wet with gas. I also pulled the start cord with the plugs out and didn't see any gas or gas vapor shoot out.

I used a spark tester and each showed a spark was happening. I don't think it was indicating a strong spark as not too long ago, I used the same sparkplug tester to diagnose the ignition on a '72 MG and the flash from the tester was a lot brighter than what I saw yesterday.

I also pulled the air filter & tube and sprayed starter fluid right into the cab, and it still would not start. About 30 minutes later, it did start, reluctantly.

All this is pointing to faulty or weak coils.

 

[bertsmobile1]

Your MG runs a Kettering ( battery ) ignition
In that case the SLOWER the engine runs the bigger & better the spark due to dwell time fully saturating the coils.
On a magneto the FASTER the engine spins the bigger & better the spark.
So at cranking speed you always get a pretty feeble looking spark.
New plugs have no glaze on the center electrode insulator so it accumulates carbon & fuel coatings that are CONDUCTIVE at cylinder pressures so the spark tracks down the electrode rather than jumping the gap , thus no start.
So first trick is a pair of new plugs.
Tipping mowers with carburettors cause the float to be out of position
On a gravity fed system that will allow fuel to overflow through the carburettor into the engine
Tipping with the carb down will allow crankcase oil to flow through the breather and into the carburettor so at worst you end up with strait oil in the carb or at best a very oil rich 2 stroke mix .

One black plug & one brown plug is usually because the diodes which prevent the coils misfiring due to the kill wire sending phantom spikes down the wire .
Run the engine without the kill wires connected and see if both the plugs look the same.
If this the case replace BOTH coils or fit a B & S kill wire subloom that has dioes in it to compensate for your bad ones which are inside the coils ( some times it works & some times it does not )

 

[slomo]

When it did start, it coughed out a bit of black smoke.

Sounds rich.

would a carburetor spacer help insulate the carb from the engine heat?

Just like the Army, if the engine needed one Kawasaki would of given you one.

Is it possible that because the mower is hot while I’m scraping out the deck, the fuel in the float bowl has boiled off, preventing the mower from re-starting.

Either boiled off or dumped into the cylinder from tipping. I've never seen a vapor lock issue on a mower. Most of the cooling air goes around the block and carb for cooling. Not to say the carb is cold by any means.

I would look at the carb float level for one. Pressure test the needle wet for an hour or more at 7psi. Maybe the needle is trickling some fuel out??

My previous mower, used from ’99 to late ’21 was a Snapper 52” belt drive walk-behind with a B&S Vangard V-twin; and never gave me trouble re-starting after tilting or when hot.

That's because it was a Snapper. Which has zero to do with engines.