Briggs popping

[Mowerflipperguy]

So here’s the deal. 2019 Briggs 33R777 0012 G1 fires right up every time. Runs rough and pops at high rpm (although it won’t get nearly as high as it should) but runs smooth at low RPM. I’ve both cleaned the OEM carb and replaced the carb, same issue. Valve clearance is good on intake & exhaust. Fuel is fresh. Flywheel key is in place. Magneto was swapped. In the video you can see a disconnected plug but that doesn’t change anything. Oil is new and at the right level. Valves bounce on each rotation (good cam). Choke moves freely (video shows this). Linkage is not restricted. All checks/adjustments made zero change to how it runs. Video link below. Any ideas?

 

[ILENGINE]

Are both valve opening the same distance. I have seen one cam lobe wear down causing similar issues with rpm and running.

 

[Mowerflipperguy]

Are both valve opening the same distance. I have seen one cam lobe wear down causing similar issues with rpm and running.

I’ll check that out and report back. Thanks for the reply!

 

[Auto Doc's]

Does it have the correct spark plug in it? I've seen the "Torch" brand cheap plugs do this. I only use the correct Champion plugs in these engines.

 

[Mowerflipperguy]

Does it have the correct spark plug in it? I've seen the "Torch" brand cheap plugs do this. I only use the correct Champion plugs in these engines.

Good call, but yes, it has a champion that looked good, I swapped it anyways with a new one and no change.

 

[Auto Doc's]

How did you check the valve clearances? "Looks good" is subjective. This thing is popping like an intake valve has poor clearance or the intake valve is leaking.

Check out Teryl Fixes All on You Tube. He has some good valve adjustment information on several different models.

 

[Mowerflipperguy]

How did you check the valve clearances? "Looks good" is subjective. This thing is popping like an intake valve has poor clearance or the intake valve is leaking.

Check out Teryl Fixes All on You Tube. He has some good valve adjustment information on several different models.

Yes sorry, I realize my “looks good” answer was probably mistaken as an eyeball guess haha. But both gaps do measure within spec. I actually went back in and checked them again thinking I didn’t have enough coffee prior, but they were spot on.

 

[Mowerflipperguy]

I’ll check that out and report back. Thanks for the reply!

How did you check the valve clearances? "Looks good" is subjective. This thing is popping like an intake valve has poor clearance or the intake valve is leaking.

Check out Teryl Fixes All on You Tube. He has some good valve adjustment information on several different models.

Both valves open right at 1/8”

 

[Auto Doc's]

I'm not sure what you are referring to when saying 1/8". If they are barely opening, then someone as already tried adjusting them and the cam lobes are very worn down. These engines were bad about eating cam lobes. I'm not sure if B&S ever got their supply caught up, but aftermarket cams are junk right out of the box for these engines.

 

[ILENGINE]

I'm not sure what you are referring to when saying 1/8". If they are barely opening, then someone as already tried adjusting them and the cam lobes are very worn down. These engines were bad about eating cam lobes. I'm not sure if B&S ever got their supply caught up, but aftermarket cams are junk right out of the box for these engines.

1/8" valve opening is about half of what they should open. And I currectly have 2 OEM cams on backorder with an ETA of October.