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Hello all,

I have a craftsman 42" 6 spd, engine model cv15s.

Recently replaced flywheel and stator (magnets had come off flywheel, and were destroyed, damaging the stator in the process), new aftermarket carb, oil and filter, spark plugs and air filter.

Problem: engine has lost power at some point this year, clear difference in how it runs when engaging with grass, versus just running with blades off.

Specific question: tried to perform a leak down test, putting Pressurized air in through spark plug hole. Gauge indicates about a 50% loss. Air seems to be exiting near (but not through) exhaust. Could someone tell me what/where that leak likely is, so I have an idea of what to expect before I take the engine off/apart?

I posted a short YouTube video, showing the location of the leak, as best as I could.
Link to video here
https://youtu.be/m8iEH0hEmqM

At some point, the engine may have been run with too little oil, or too much, or both. Having run the mower for a bit after I changed the oil, my girl checked the oil, thought it was low, and added some. When I checked it later (after it had been again run a couple of times), it had too much oil. It had synthetic in it, so I did another full change, with new filter and correct amount of Dino. Possible I got distracted and somehow failed to put oil (or enough oil) in during the oil change, so maybe it was run low on (or without) oil. I don't know, and don't claim to be infallible. It was definitely run overfilled with oil, and with synthetic.

I'm not certain if the loss of power showed up immediately after that kerfuffle, or if it had presented earlier this summer, as it's my girl's mower, and I hadn't done much riding/cutting this year.

Thank you so much, in advance.

Your exhaust valve isn't closed, or badly leaking, as well as the exhaust gasket or pipe.

Do you have the engine locked at TDC?

Blown head gasket.

Also, be carefull doing this. You could easily lose a finger.

I believe it was at TDC, yes. Admittedly, I am new to leak down tests, and don't have much experience with small engines (plenty more with car and truck engines).

It definitely didn't seem to be coming out of the exhaust pipe, itself, but from either the exhaust gasket or really between the cooling fins of the engine. Obviously, I can't be sure, though.

How would you lose a finger, btw? Thank you for the warning!

I'm with cpurvis .Head gasket, especially since you said it's not coming through the exhaust.

When pressurizing through the sparkplug, trying to test the rings, it is real hard to get it to stay at TDC, so folks might take off the flywheel cover and lock it in place, some might try to hold it by hand. And it can easily {violently} make the flywheel spin, and shear off a finger on a coil or something.

It could be a head gasket too, putting the engine at TDC would help confirm this.

Taking off that head is pretty easy to do. You have replaced a lot of more difficult items already.

Thank you so much for all of the help, and the words of wisdom.

If it's not that difficult, I will likely try and take it apart at some point when I see her this weekend, and see what I'm facing.

Much appreciated!

Yeah, look at the gasket before you try to take it off, it will come off in pieces, the graphite sticks to both surfaces normally. Put up some pics too!!