Here is a good one you guys to figure out.

[StarTech]

33R877-0002-G1 2014.

Would not idle below 2500; unless, when it did it was backfiring through the carburetor so bad that I actually seen the flywheel to kick back. This had at time kill the engine. I have since repaired the problem and it now idles at 1750 without a problem.

Another shop sold this mower is this condition and even put on a Chinese clone carburetor trying to resolver the problem. He claimed he repaired the problem but it definitely was never fixed. This shop is an insult to us true mechanics and he actually ripoff the customer as I got to bill for my work even the customer had already paid out $800 for the used Craftsman 46" cut mower.

 

[slomo]

Ignition timing, cam timing way off, mower hit a log chain or a stump. Check the flywheel key and blades.

Side note, don't get into a habbit of idling down a mower engine. Two things, poor battery charging and poor oil lubrication.

slomo

 

[StarTech]

Ignition timing, cam timing way off, mower hit a log chain or a stump. Check the flywheel key and blades.
slomo

Nope, nope, nope, and nope. And the steel flywheel key is fine. And the deck is not engaged so that not in the picture.

 

[Rivets]

Coil installed upside down, or the wrong coil or improper gap?

 

[StarTech]

Coil installed upside down, or the wrong coil or improper gap?

Nope. Although I did need to set the gap twice my normal gap setting due to keep it from rubbing on the flywheel. But that did not affect the problem; otherwords, it didn't improve or make it worst.

A real brain teaser. What some hints from the troubleshooting I did? The problem was there with the engine both unloaded and under loaded.

 

[bertsmobile1]

Well this is starting to sound like the wrong flywheel was on the engine if you needed to double to armature gap .
The one & only time I have seen that was a no brand Chinese Honda clone .

 

[Scrubcadet10]

Faulty spark plug?

 

[StarTech]

Well this is starting to sound like the wrong flywheel was on the engine if you needed to double to armature gap .
The one & only time I have seen that was a no brand Chinese Honda clone .

Nope, The gap is now set at two repair tag card stock thickness. Now at about the max specd gap. Normally I set them at one stock thickness.

Everything is original from 2014, except the carburetor which was changed by the other shop because of this problem around Christmas 2020 because it was Nikki carburetor. Something I don't understand is why everyone hates these easily fixed carburetors. It was just needing cleaning which is why I initially had the customer return the mower to the other shop for repairs under warranty. (hint of root cause)

Why the shop returned the mower in worst condition than before just tells me the mechanic didn't know what he was doing and was just guessing at the problem.

I can say everyone so far is being mislead down the wrong path. It was not a mechanical or electrical timing issue but it was a serious tuning problem. (Another hint)

It was not a blown head gasket (leak down only 20% which is great for 7 year old Briggs) or a valve clearance problem either. The valves were out of adjustment a little but after adjustment nothing changed.

I actually fixed the problem without using any additional parts just a modification. Now I just got work on the deck vibration problem but I suspect that is just out balance blades.

 

[StarTech]

Faulty spark plug?

Nope. New and tested was installed from a working engine. Done to just check it off my diagnostic list.

 

[Fish]

Bad cam?