The mustang has rough idle and won't smooth out

[Helltime]

Me and my dad are working on an 83 mustang GLX 5.0 5speed and we can't get the idle to smooth out. We put a new edlebrock carb, plugs, wires, cap, rotor and coil and tuned the carb and the idle will not smooth out because it still has a miss. Would a small vaccum leak cause this. Any suggestions will be greatly appretiated. Thank You

 

[BlackGT89]

Me and my dad are working on an 83 mustang GLX 5.0 5speed and we can't get the idle to smooth out. We put a new edlebrock carb, plugs, wires, cap, rotor and coil and tuned the carb and the idle will not smooth out because it still has a miss. Would a small vaccum leak cause this. Any suggestions will be greatly appretiated. Thank You

Is it a ramdom miss or a constant miss ? If it's a constant miss try to isolate which cylinder is missing and what is causing the miss. Take a rag and place it under / around the tailpipe and see if you get a flapping sound as if it's trying to suck the rag back into the tailpipe. That will at least tell you which side the miss is on.

 

[Helltime]

We think it is cylinder 8 because that doesn't seem to make any difference when the plug wire is clear off. We do have a vaccum leak but at 800rpm it is pulling 21pounds of vaccum even with the leak.

 

[BlackGT89]

We think it is cylinder 8 because that doesn't seem to make any difference when the plug wire is clear off. We do have a vaccum leak but at 800rpm it is pulling 21pounds of vaccum even with the leak.

If it's a constant miss on one cylinder and it is getting a good spark it sounds like it's loosing compression in that cylinder. If fixing the vacuum leak doesn't clear up the miss, it might be time for a compression test.

 

[Helltime]

Thank you I will see if I can get my dad to fix the leak then hopefully it will run smoother. The idle doesn't bother me it just bothers my dad.