The Stovebolt Site Forums The Shop Area Engine Shop Engine sputtering

Pretty suddenly my engine started to sputter at high rpms, if you get on it, it smooths out, otherwise it sounds pretty crappy, kind of sounded like fouled plugs and they might have been a touch, but cleaning and new ones didn't fix problem.
No hesitation from idle or anything like that, no loss of power.
I can't remember exactly now, but it just kind of started doing it when I was still driving it, but parked it for the summer because I was busy.
So trying to figure it out. Points should be fine, changed to an older but ok cap and rotor, new spark plugs, changed in line fuel filter.
What next?
Oh, and also, not sure why, but the rear two spark plugs were discolored on the outside of engine, not sure what could cause that, maybe heat....
1961 261 engine btw, rebuilt about 2000 miles ago

Probably the condenser. Same symptoms happened to me with a '66 Mustang and '56 Cadillac. Condenser in Mustang only had 1500 miles on it. Modern ones are junk.

Get one of Jon G's 200,000 hr condensers.

I have one, actually 2, I should check and make sure it's making good contact.

OK then. Check for vacuum leaks.

What the carburetor story?

Professionally rebuilt carb, jet bored very slightly over for 261 engine (off a 235). Ran super well, haven't really ran ethanol fuel through it, I'd think it should be good, only a year or so old and it's longest break was this summer. I will definitely check for leaks though, and make sure the vacuum advance is working.

The gas tank should probably be drained and cleaned, but with the filter, unless there's water in it, it should be good. Since it was running fine with whatever was in there before, but just guessing that it's fine is kind if a sure way for problems.
Idle is okkkk, but not as good as it should be.

That can be caused by too much timing. Try running it with the vacuum hose disconnected from the dist vacuum advance. Plug or put a piece of tape over the vacuum outlet.

George

What does this little tube in the carb do? Took the air filter off for a peek and pretty dirty.
Can see light through air filter 🤦🏻‍♂️
Inside the carb itself doesn't seem very dirty, but that little tube sure is. Not sure what to do from here.
I wonder how helpful eating a healthy diet of dirt has been for my engine.

That tube is a vent to the fuel bowl and should not be dirty. Possibly fouled some passages in the carb. I would take the carb apart and give it a thorough cleaning. Take note of what is in the bottom of the fuel bowl.

I don't know what kind of air filter you have but the stock oil bath filter is the best. Keep the oil level up and they work every time, all the time.

Ok, will do, thanks jethro, I'd like an oil bath one, but didn't have one with the truck when I got it.

My only concern (perhaps unfounded) with the oil bath is mine is the kind you can't remove the element for cleaning. Guess they can be cleaned well enough with lots of sloshing mineral spirits. You seem to have good success with it though.

So I took her apart, and there's a touch of silt at the bottom but nothing crazy, Not sure where the issue would lie

The big rigs still use oil bath air cleaners. They never "choke up" with dust. Just clean the bowl and fill with oil. The oil keeps the mesh clean.
.