318 running rough...

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Ozzy

Ozzy

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For the past 2 years I've been restoring a '67 Barracuda. The guy I purchased it from claimed that it had a 273 that was changed out for a '68 318. How many miles he had no idea. I recently rebuilt the carb and installed an electronic ignition. Afterwards, it ran very rough. I tried to adjust the timing, but noticed the line on the HB was jumping around. Figuring it to be the timing chain, I replaced it. Gears looked fine, the chain was pretty loose (I did find out that the engine is a later year than '68, due to the gasket on the pan end).
Started it back up thinking I'd find an improvement, but the timing is still jumping. Any thoughts?
 
Do a compression check, I bet you find a burnt valve or a flat cam lobe.
 
I was once told to pay extra attention to the bronze bushing in the block that the distributor drive gear spins in because slop there transmits ....................don't know if this helps........
 
If it didn't do it before you put the electronic ignition in you may have a bad module. Put the points distributor back it a see how it runs.
 
Check the valve lash. All pre-69 273s were solid lifter engines. The only hydro was the 69s
But if it ran fine before the mods then;
1) confirm the firing order
3) confirm the reluctor gap
5) confirm the timing ring on the balancer is tight
If all is good then
with the timing light hooked up,and the Vcan defeated, slowly bring the Rs up. A bit of jumping around is ok like 2 to 4 degrees. But if the timing is jumping 10, 12, of out of sight and the strobing shows dropped sparks, AND, AND the engine won't take rpm very well and starts bucking and farting,etc, then:reverse the polarity at the pick-up coil, and reset the base timing.
Then go back to; If all is good
 
Last edited:
AJ/FormS said:
Check the valve lash. All pre-69 273s were solid lifter engines. The only hydro was the 69s
But if it ran fine before the mods then;
1) confirm the firing order
3) confirm the reluctor gap
5) confirm the timing ring on the balancer is tight
If all is good then
with the timing light hooked up,and the Vcan defeated, slowly bring the Rs up. A bit of jumping around is ok like 2 to 4 degrees. But if the timing is jumping 10, 12, of out of sight and the strobing shows dropped sparks, AND, AND the engine won't take rpm very well and starts bucking and farting,etc, then:
Then back to; If all is good
Click to expand...
That's exactly what's happening...the timing is jumping all over, and strobe isn't lighting consistently, engine is bucking/farting. It wasn't running this bad before the distributer change.
 
Ozzy said:
That's exactly what's happening...the timing is jumping all over, and strobe isn't lighting consistently, engine is bucking/farting. It wasn't running this bad before the distributer change.
Click to expand...

It's sooo easy to get cylinders 5&7 swapped at the plug wires.
Also check the distributor for up and down play in the shaft.
Timing stuff should all be changed as a set. (not that this is the problem)
Another thing is the idle speed since if too high can cause mechanical advance to try to come in at idle.
 
Post 5 edited due to fat finger typing lost a sentence,
AND, AND the engine won't take rpm very well and starts bucking and farting,etc, then:reverse the polarity at the pick-up coil,and reset the base timing.
 
Well, throughout my troubleshooting, I found that my coil went bad. It quit sparking altogether. Hoping this was somehow tied to my issues I've been having, I replaced it with a MSD high vibration coil. Apparently, this one can be mounted on its side which works better for the space I have. Anyway, I have great spark now, but still have the issues with the timing. I'm thinking Sireland67 may be right about a valve/lifter/cam problem. I'll be taking the valve covers off and checking the lift on them. Any advice for determining what's good or not?
 
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