Help! Engine bogs at take off and smoke from oil breather

[Bigb55]

Help! Ok engine gurus. My '74 w/sm456 has an unknown 350 with some sort of cam. unknown heads , I believe stock. No idea what has been done to it or mileage. Edelbrock 1406 carb, that appears to be working well.

It has ran well for the last 3000 miles. Recently it has started to randomly bog down on acceleration at low rpms often stalling the engine. Followed by a hard restart like it got flooded. It also started puffing smoke out of the oil breather cap on pass side head. Some smoke on startup out exhaust.

It also now has a noticeable knock sound coming out pass side exhaust. But doesn't appear to be noticable at the engine. Tried stethoscope trick on each cylinder area. All sound similar no knocking. Checked exhaust it does not tap on anything or wiggle around.

Initial timing with no vacuum advance is ~12 degrees at idle set to around 800-900.

Any ideas?

Compression test and spark plug inspection is on the list when I have more time. I'm hoping for worn out valves. But I'm thinking piston rings and cylinder damage. And the knock out exhaust makes me think bearing.

Here's a video of it running and the knock sound out the exhaust.

 

[Bent77]

Run the compression test first

 

[imiceman44]

Run the compression test first

Yeah he can look at the spark plugs while pulling them out to do that but yeah, sounds like exhaust valve to me

 

[Bigb55]

Little Update, haven't had time to do a compression test. currently getting another truck ready for paint. So need the '74 mobile to drive around.

But I did replace the PCV valve (old one was stuck closed), oil breather cap, and the corresponding grommets. Also adjusted the choke, idle mixture, and idle air setting and Cleaned the carburetor up.

It's running much better and way less smokey. Also by getting the PCV system fixed, I found quite a large header leak at the #8 exhaust port.

Still no knock at the block and Only out the exhaust.

Confident it's sticky valves and will confirm with a wet and dry compression test after I finish paint in the other truck.

If it is the valves, I'll probably buy a set of rebuilt ones to slap on. And rebuild the old set as spares.