What's the model & Type numbers?

did the WHAM only start after you adjusted the valves?

Model: 313777
Type: 0163-E1

And yeah, the wham started after the valve adjustment. It sounds like a hammer hitting the block. Could it be backfiring?

Exhaust calve is supposed to be .006" +/- .001", but that shouldn't be the problem.

I'd remove the valve cover-
Slowly crank the engine by hand and observe the rocker arms/push rods.

I'm thinking you may not have a push rod "seated" in the cup properly.
IF it's overly loose, the ball may be catching the "edge" of the cup instead of being seated down in the cup.

Thanks for the tip, I'll check it out

From what you have described, it sounds like the engine may have suffered a loosened exhaust valve seat.
When the engine first became hard to start........and you checked the valves........was there a lot of looseness in the exhaust valve?

OK,
I just turned it by hand and now I'm really concerned. The push rods are seated correctly, however when I get to the point in the cycle when the fuel is injected, there's a pressure sound, like when you pinch a balloon nozzle, and then fuel comes leaking out of the valve area. The intake valve is moving though... This doesn't sound good.

When I first gauged the valve clearances, they were at about 0.010"

Thanks for the continued help

"then fuel comes leaking out of the valve area."

Are you describing a blown head gasket?

What do you mean by "valve area"?

By "valve area" I mean the compartment covered by the valve cover

IF you are talking about "fluid" getting pushed out the head gasket near the push rods, it sounds like a blown head gasket.

There's multiple places in "the valve area".

I suggest you go to the Briggs website and download the IPL for your specific engine.
It has exploded drawings and proper part terminology.

Thanks for the suggestion. The fluid is definitely gasoline, and it's coming from behind the push-rod guide. It's running out the shaft that the push rods come out of the block from. Does that help?

I understand the head gasket might be blown, but I'm struggling with understanding what I could have done in the valve adjustment that could cause that. It wasn't leaking before. And it was running a little rough, but nothing like now.

"It's running out the shaft that the push rods come out of the block from. Does that help? "
Nope- It's totally confusing.

Download the IPL!
It'll also show you how the parts inter-relate to one another besides allowing you to use the correct names.

Well, if yo have LIQUID gasoline spraying out into the area I indicate with red arrows in the photo, you not only have a blown head gasket, you probably also have a carburetor leakage problem.
But neither a blown head gasket or a gas leaking carb is going to produce the hard metallic knocking you are reporting.
However, gasoline leaking into the combustion chamber CAN contribute to a blown head gasket because liquid inside the combustion chamber equals a hydrostatic lock condition which can eject entire pieces of head gasket sometimes.

Thanks Mownie! That's exactly where its coming out.

Bill - I did download the IPL.the part the gasoline is leaking out of is the cylinder assembly (part #1), but I was trying to be more specific (e.g. behind the rod guide).

Anyways, any ideas how everything blew after I adjusted the valves? And is it possible to make relatively quick work of this by moving the piston to BDC? This is a 15 year old motor...

Thanks!

I can't see how adjusting the valves would be related to blowing a head gasket.

IF the gasket was "slightly blown" AND the intake valve lash was so loose that the cylinder wasn't getting a full "charge" of air on the intake stroke, than possibly allowing the engine to develop more power than it had been, might have been enough to put the gasket "over the edge".
That's getting to be quite a stretch though and still wouldn't be the root cause.
Besides, you'd probably have trouble starting the engine for multiple reasons. (compression release not functioning amongst them)

How would putting the piston @ BDC be useful?

IF you are going to change the head gasket, you want the piston in a position where both push rods are loose.

The fact you asked that question makes me wonder about the procedure you used to adjust the valves.

Thanks - I've never done a head gasket, or even that much of a tear down, thus my naivete on that. The procedure I used for the valve adjustment was to move the piston to 1/4" past TDC, adjust to 0.004" clearance with the rocker arm, and then tighten the set screw to 45 in-lbs.