Sputtering on Hard Acceleration

[jimkov]

I just changed the oil in my 71 Challenegr RT for the first time. 383 with a mild cam, six pack, and a 4 speed. I contacted the past few previous owners but the paperwork on the engine build from 2018 by Mopar Madness in Colorado was lost and I reached out to the shop but never received the build sheet after a few requests.

I went with Driven HR-6 10W-40 since I'm in West Texas and there are many days over 100 F.

The issue I am having is a sputtering/clunking noise in hard acceleration. It sounds like the noise when you are about to stall the engine at low speeds. It's does not seem like a carb bog. The acceleration is very close to ideal. I'm also having issues with the engine continuing to run after turning the car off.

Drained 4.2L of oil and 4.4L filled it just below the full line.

I changed the PCV valve. The old one had a thin costing of the new oil in it and the carb port it was attached to. I've played with the setting in the car and made it a lot worse. I got it back to the settings I had prior to the oil change but the sputtering/clunking and the enginer runoff on turning the car off still persists.

I'm thinking maybe an internally sticking accelerator pump, leaking piston rings, improper oil grade for my setup, possible over filling due to an after market dipstick. If anyone has any suggestions please share to help guide my next action.

 

[pschlosser]

Okay, several thoughts and ideas. Bear with me.

Are you accustomed to the sound of pinging? when the engine timing is advanced farther than the grade of fuel can tolerate? Is the sound you hear, pinging?

I don't think a (perceived) less than ideal engine oil weight is the issue. But I WILL say, I'm no longer fond of fully synthetics, and have gone back to pure dino oil plus a ZDDP (zinc) additive.

Yea, you want to nail down that clunking. What you describe sounds mechanical, and could be a spun rod bearing, or another issue that may result in a catastrophic failure. Go easy until you work it out.

Dieseling, or engine run-on after shutoff, in my experience can result from a couple of factors. 1. engine timing too far advanced. 2. carbon build up in the combustion chamber. #2 is easily resolved with a water bath. and given that mechanical sound you described, check the timing and maybe back it off a 5 or more degrees, until you figure things out.

leaking piston rings will leak, all the time, and typically result in smoky exhaust and oil consumption. Not just "when you get on it." but if it smokes on hard acceleration or deceleration, let us know. oil weight issue? I'm not so sure. a 10W40 seems well within tolerances. That Driven motor oil is hella expensive, more power to you.

I don't know what carburetor you have, but the Carter AVS variants wont cause this issue, either. The accelerator pump cannot really "stick." The (historically OEM) leather accelerator pump can wear, and pump less, but it cannot really stick, given the way the linkage is set up.

An aftermarket dip stick? Well, if the oil level is wrong, or too low, the idiot light would come on, when the RPMs are high. And if the level were too high, checking the oil after a hard run would show bubbles on the dipstick as the oil became frothy. So both of those are easy to clarify and check.

Too much oil may indeed sputter up into the PCV valve. And if so, into the hose and fitting to the carburetor. That may not be a failing PCV, but I cannot say from my chair.

Can you clarify what you mean or did by the statement "I've played with the setting in the car and made it a lot worse." what setting? from within the cabin of the car? You got my curiosity.

 

[cuda joe]

engine run on . it could be over heating or the idle turned up to high some times people turn up the idle to keep it running because it's not running right . vacuum leak ; bad plugs ;ignition problems ; ect . you could pull out the plugs to read them . google how to read plugs . don;t get on it while it;s making that noise

 

[cuda joe]

first make sure you have good oil pressure

 

[FrankenKuda]

Diesel: Also check that the carb float/s are set right. If they don't shut the flow of fuel off when the bowl is full you'll overfill and it goes right up the vent.
Another thing to look at is the timing chain. Take the distributor cap off. Turn the crankshaft both CCW and CW. Verify the distributor rotor starts to turn almost immediately. If not, the chain is worn and that will throw your timing off both at start up and shutdown. You "may" also see it with a timing light. The timing mark may move around instead of be solid on a mark.
Without knowing your compression ratio, be sure you're fuel is the correct octane level.

Your sputtering/clunking problem may be related to the jets of your carburetor being too large. That's not to say the other opinions given previously are not also very possible. Just for trouble shooting purposes, you could also only run on the center carb and see if the problem goes away. The idle circuits on the two outboard carbs may be contributing too much or they're not shut all the way during idle.

I think the site could add about another dozen+ things that could be contributing factors if not the primary cause.

Cuda Joe is right though. Read the spark plugs. One may not tell the whole story. Pull all 8. Do they look the same and what do they look like? That will tell you a host of problems. While the plugs are out you can try my trick of looking at the distributor rotor to verify the chain appears good. While you have the cap off, look at the electrical and mechanical bits of the distributor. Weights are free and cap/rotor is not burnt or corroded. Be sure the timing is right. Investigate a method called static timing. It gets you past the influence of the vacuum and weights of the distributor.

Good luck