10.5 HP B&S Backfiring/Popping.

10.5 HP Briggs and Stratton OHV Model 215807-0324-E1
On a Murray rear engine 30" cut riding mower.
This is an older mower (2005 I think, that I purchased second hand)

I am hoping someone can give me a few pointers as to what I should look at next. Thank you in advance.

Details:
The first time I mowed the lawn this season the mower ran OK but after that it would pop/rough idle and want to stall out when engaging blades.
At least until it got warm. Even then I could tell it had less power.

Since I then I have done the following, Some of it because it looked like it needed and others trying to fix the issue.
- Replaced carb
- Cleaned fuel tank (though the inside looked good. It has mostly had non-ethanol gas)
- Replaced all of the fuel lines and fuel filter, along with new gas cap and fresh gasoline
- New air filter. Though it does the same thing with filter removed.
- New spark plug and magneto
- Pulled Flywheel to check timing key.
- Compression test (145ish PSI), I haven't been able to find a spec for this. I have a leak-down tester on the way though.
- Oil Change
- Valve adjustment (0.005 on both intake and exhaust) based on a chart I found for Briggs engines.
- Cleaned debris from around governor.

The engine starts right away now and seems a bit stronger but it is still popping. The popping occurs at all engine speeds. choke and no choke.

I have a short YouTube clip of the problem but I do not have enough posts yet to allow me to post links.

Regards,
Zach

Water in the fuel would give you a pop, but you said that taken out all the old and replaced it with new, I would remove the valves and take a good look at them, you may need to lap them, you didn't say if the popping was from the intake or exhaust, so I would go by exhaust...!

You could try and send me the link to video in a PM.

Yes what is your you tube channel name ???? I'll check it out also ........ I agree withe the valves being out of whack...

Did you check for push rod travel on both ??

Run it for 10 minutes then pull the oil dip stick..... If it's smoking are steaming it's a head gasket . but you have real good compression soooooooo.....

Let us know Mon Ami....

Thanks for the replies.

Sorry from the video you can see its popping from the intake and I removed it at the end when forum would not let me post.

I replaced the fuel twice from different sources. Just in case.

My Youtube is Zach Morris
I attempted to add the link again with a dash in front below.

-https://youtu.be/-T94PXk_EIQ

Sorry I just saw the push rod comment reading the post again.
I watched the push rods and valves while moving the flywheel by hand several cycles and I spun the push rods in place to feel for anything out of place.
I did not pull the push rods out yet as I didn't remove the rockers.

-Zach

If you pull the rods check for bent rods also ~!~!

A longer video would be nice and then showing it with the blades engaged also ~!~!

Thanks. When I get a chance to work on it again I will grab a longer video.

Going by the video you have a problem with the inlet valve.

Thanks for the comments:

I was thinking intake valve issues as well but I am no expert so I wanted some other opinions.
Once my leak-down tester arrives I will get a baseline and then pull the head to check/lap the valves and inspect rods and all again.

Looks like I will be getting some exercise with the push mower for a bit. haha

Thanks
-Zach

Update:

The leak-down test was in the green. It took some effort to get the thing to sit still in order do the check.

I pulled the head earlier today. My untrained eye doesn't see anything obvious other than carbon buildup.
-The head gasket appears to be in good shape to me. (I will be replacing it anyway)
-The rods appear to be straight.
-I double checked to make sure none of the supports for the rocker arms had backed out but they look firmly seated.
-I pressed on the valves by hand. The intake valve seemed to take a bit more pressure to move but not much.

My plan now is to get the tools I need to get the valves removed, lapped and a new gasket set for putting everything back together.

Pictures
https://drive.google.com/drive/folders/14B4A2Y11pDJ5GUmQ33Ao08QwZnygWmCI?usp=sharing

Slightly longer video than before. I forgot to get a clip with blades engaged.
https://youtu.be/XouGjm1CsFU

Thanks,
-Zach