Any small Engine guys on board??

[Jarmo]

Many small engines have a small bump on intake cam for compression release and if valve lash is big enough then it does not open intake valve for compression release and starter can not turn it over.

[modok]

the famous BRIGGS and stratton, PATENTED "ez-spin starting system" was.....a cam that held the intake valve slightly open through the compression stroke, as compression release. Idle quality suffered but...who idles a mower?

More advanced designs had a stamped steel dingle arm on the cam, that was a compression release at low RPM but would swing out of the way when started. Eventually they ALL had something LIKE that, one form or another.

What "grunting" is I have no idea... but why valve lash could impact starting....that'd be my guess, is excessive intake valve lash could be bypassing whatever compression release feature they are using.
Of course tight lash would be a problem too, but for the usual reasons.

they start fine, or perhaps better without the compression release, but it takes a stronger arm to do it, or stronger starter motor. Flywheel has to spin up fast enough to make the ignition work.

[Dave Koehler]

Agreed that the loose lash and the compression release bump on some engines is a real thing.
Maybe not this time but certainly a suspect. I would verify the lash.

OP, you stated everything electrical is fine but have you tried a different battery?
Those baby batteries don't have a lot of life or grunt in them. I had the same thing with my old JD 318 this year.
Well, it began last year when it started that slow roll start up.
I found it odd since this Onan is one loose, noisy, ready to kick a rod out piece.
This year it got worse.
Throwing the battery charger on it did nothing.
Hmmm, tester read the battery as being next door to toast.
New battery and it started up quickly.
On a side note this battery was 1 yr and 1 day old. 1 day past free replacement.
Shortest life I ever got out of one of these.

I ran into the tight lash version of this last month.
Neighbor next door has a Kubota Lawn tractor. I noticed over time it had to crank longer and longer to fire. This year was the last straw. After Listening to it for the umpteenth millionth time I told him to bring it over.
Checked all the usual suspects. I don't recall the number but the lash was pretty tight. Reset it to the max factory setting. Bingo...back to starting in a normal manner.
I am guessing that when cold, hi hours, loose guides and some carbon build up was holding the valves up just enough to act as a compression release.

[treyrags]

I have sprained my wrist bad a couple of times on 14 horsepower pull start engines like this that we're out of adjustment and the compression release did not work and kicked back on me. Not fun

[modok]

I could recite the 396 firing order as the Engine grunted over, one compression stroke at a time.

Put a longer duration cam in it, and the starter will be able to spin it a lot easier

[Dan Timberlake]

I like to do a voltage drop test while cranking. It is surprising (at least to me) how machinery seems to conspire and continually create new ways to fail.

Just sitting here I recall I've been bit twice by simple spade connectors when the female wore to cause a lose fit with the male.
The last time was just last weekend when a neighbor dragged her unconscious John Deere riding mower over to our house.
Turn the key to on, the electric carb main jet clicked on, but the hour meter remained blank, and of course no crank.
Checking voltage all over the place produced some crazy voltages between 5 and 10 volts at some locations where there should have been full battery 12.X DC volts.

It turns out this JD joins nearly all the grounds together eventually to a single wire that crosses over the chassis to the same point where the fat black battery ground cable bolts to the chassis. About 8 inches upstream, well hidden in the dark tight nether regions below the battery and behind the engine, is a single spade connector. THE spade connector. Snip, crimp, hopefully good for another 10 years.

The volt meter sniffed out the bad connector like a blood hound.
It would have taken a "shot gun" replacement of the $100 front wiring harness to inadvertently fix it.

[Dave Koehler]

Congrats.
Amazing little detail isn't it?
I just got done convincing my son in law of this. He was ready to trash a perfectly good engine.