26 hp briggs v twin wont regain power

I have a four year old Grasshopper 226v zero turn mower with a 26 HP commercial v twin Briggs and Stratton engine. It has always run and cut great. This year a belt pulley that attaches to the transmission came off. I tried to reattach it but it kept spitting out screws immediately after starting. I took it to my local dealer and they replaced the pulley and did a routine service. When I got it back it mowed great for an hour. I stopped to move some debris. When I started it back up it sound like it was running on one cylinder. I called my dealer and dropped it off. They had it for two weeks saying they thought it a fly wheel issue and had to call a Briggs tech. They brought it back and said it was fixed, and no charge. Well it ran better but still backfired, would only run with the choke out full, and had limited power. I took it to a Briggs and Stratton authorized repair shop. They pulled and cleaned the carb, replaced the fuel pump, and said someone had adjusted the exhaust valves wrong. The said it was running much better but is underpowered and I should replace the engine with a Kawasaki (I’m considering that idea). Well now power wise it runs about 75-80% of what it originally had. It runs with the choke in and is smooth, but it’s like it’s lost a gear. I still smell it’s running rich and there’s a metallic sound when running, almost like the pinging of valves in a car with bad gas. I have run sea foam through it twice and switched gas brands. Any ideas of what happened and how to fix it?

Please do not repost your original question it gets very confusing.
If no one responds then go to the emojies on the right .
hit the "more" link then post "anyone" .
you can use the reply with quote if you like.
A lot of people use the "posts since your last visit" feature and doing as per above elevates your post to the top, called bumping.
And of course we will also know how long it has been since your original post
:anyone:

Need the numbers off the engine itself. Start engine up pull one plug off if it quits the other cyclinder is not good in some ways. Firing,fuel,compression. Be best at that point to check and see what is missing. Then might do a compression test and followed by a air pressure test to the cyclinders or better called the leak down test to see and hear and feel where the loss is in you engine. Check your throttle cable and make sure it pulling to wot. Report back with the engine #'s.

The serial number is 14 0620 YG 31570

bondjohnston said:

The serial number is 14 0620 YG 31570

Click to expand...

The needs different engine...underpowered is an excuse by a mechanic who can't fix it.

He is saying he knows more than the engineers who designed the mower.

bondjohnston said:

The serial number is 14 0620 YG 31570

Click to expand...

That number is not going to tell what the engine is. Model number will be stamped into one valve cover and be 44----. Type and Code numbers will be there also.

Walt Conner