I have a 1983 d150 with a flat 6. The motor runs very rich, and when I put a timing light on it the timing mark moves 5° back and forth what could cause this

Does it still have the Lean Burn system installed?

is the 5-degree flicker just at idle or at mid to full no-load engine speed?

It's likely the timing gears and chain needs to be replaced.

Does the engine turn over a bit before the rotor on the distributor begins to move (when checking back and forth?

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The lean conversion has not been done yet. All of the emissions and vacuum lines are off the motor the carburetor has no wires The vacuum advance on the carburetor is plugged. And there is no choke. I have only tested the timing marks at an idle.

The Lean Burn system uses engine vacuum and engine temperature to sense engine demands and to then set ignition timing. The Lean Burn computers were not reliable, however with the vacuum lines removed it has no chance of being accurate with its outputs.
Your best solution is to completely change over to a HEI ignition. Since the carb has no input wires the carb can stay. For the best results you should disassemble-clean-rebuild the carb. You will need to replace the distributor with a 70’s Mopar slant six distributor with a mechanical and vacuum advance.

Is the carb a one bbl or a two bbl. The carb should have a choke. My 83 D150 had a factory BBD-2bbl.
Concerning the timing chain. If it is the original timing chain and gears, then yes it is likely worn and stretched. That replacement can wait until you do an engine rebuild.

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Doo Ron Ron and the Duke of Earl are friends of mine.....
https://www.youtube.com/watch?v=uX8Nj8ABEI8

Thank you so much for your help it is a Carter one barrel

You SURE? I've seen so many people mistake a Carter BBD for a 1 barrel, I've been in more than a few arguments about this. Strangely especially on 318s which also used the BBD very much like the one on a /6 (but not identical) and the 318 never got a 1 bbl carb.... But there are people that insist that carb is a "1bbl". Just because the air intake is round and only has 1 round choke butterfly does not necessarily make it a 1 barrel.
If it is in fact a 1 barrel Carter someone has swapped them as the last /6 that came from the factory with a Carter 1bbl was about 10 years older than your truck. If that is the original carb for the truck and it is a Carter it will be a 2 barrel. Open the choke and look down it. That's where you'll see the round choke horn open up into 2 smaller barrels.

A picture of your carb could solve this.

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Yup.

I am 70 years old I have worked on cars my whole life I rebuilt a 327 68 Corvette completely rebuilt a 235 with a 62 impala it is a Carter 1 Barrel the previous owner said they had replaced the carburetor so you could be correct but this is definitely a one barrel and also the intake is only for one barrel not a two barrel. I am new to the Slant six i have a lean burn problem and other things going on as far as I have researched in all of my books this truck did come with a Carter one barrel from the factory. But I am not as familiar with this engine as I am a Corvette 68 motor or a 62 235, I appreciate any help you guys can give me!

Robin.....your age and experience (with Chevies) has no bearing on your query. Your original post claimed you had a "flat 6" in an '83 D150. We here typically CONFIRM what's being talked about, so as to give out CORRECT info. (after all, YOU are our eyes and ears at the moment)

Now, how about we all CONFIRM that it's a ONE barrel carb, so these gents can help you out? Those Carters can look like a one barrel from the outside, but a look down the throat, and you see two venturis.

Roger

The number of carburetor mounting bolts would be and indicator as well, right?
Two bolts for a single barrel, four bolts for a two barrel.

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1975 Dodge D100 225 c.i., HEI, Parallel Offenhauser, Motorcraft 2150, 904 auto, 9.25" 3.55:1

I cannot seem to upload pictures of the carburetor it has one Venturi and two bolts and it says Carter. If I can figure out how to upload pictures to the site I will send pictures of the carburetor

[img][/img] looks some thing like this?