Ignition problem? Rough idle, dies

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Mac442

Master Mechanic
Apr 25, 2020
257
384
63
Ocean County, NJ
About a week ago my 383 sbc started running like crap. It won’t idle unless foot is on gas, dies. Runs rough when holding gas. Gas smell really bad, it almost seems that it’s not igniting correctly.

all components of the engine have less than 1500 miles on them. Carb is a Holley 4150 750. I tuned it with vacuum gauge and it ran great about a month ago. Power valve is good.

Running MSD diet, 6AL box and blaster SS coil. when I tuned it and changed the advance springs I noticed the rotor looked a little whooped despite having so few miles on it I replaced it. After it started running rough I remember this and checked the cap and the carbon button was almost gone! I got a new cap today thinking that would fix my problem but no luck!

any thoughts! I’m thinking of replacing the coil and plugs next.

side note, when it initially start when cold it runs normal for about 10 seconds then the rough/missing starts.
 

MrSony

Geezer
Nov 15, 2014
6,793
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Beefed up qjet time
:D
 
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pontiacgp

blank
Mar 31, 2006
29,270
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Kitchener, Ontario
with a problem like that I would change the oil, it's polluted with gas. You need to be carefull with a carb that is dumping fuel, it will wash the oil off the cylinder walls and you can ruin the rings and bore.
 
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Mac442

Master Mechanic
Apr 25, 2020
257
384
63
Ocean County, NJ
with a problem like that I would change the oil, it's polluted with gas. You need to be carefull with a carb that is dumping fuel, it will wash the oil off the cylinder walls and you can ruin the rings and bore.
Thanks! I worried about this too. I’m going to take a look at the carb in the morning.
 

Clone TIE Pilot

Comic Book Super Hero
Aug 14, 2011
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Galaxy far far away
Most likely a vacuum leak. Lean exhaust smells much stronger than a rich exhaust. Lean mixtures also are hard to ignite and can mimic ignition issues.
 
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Mac442

Master Mechanic
Apr 25, 2020
257
384
63
Ocean County, NJ
Pulled the needles out of the carb this morning before work. A lot of junk in there! Looks like the O-rings are falling apart too.

8134D81C-21A5-4B87-9D55-A7111E5F1721.jpeg


looks like I’ll be going through the whole carb again. Weird that the O-ring disintegrated. Don’t have many miles on the carb at all.
 
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GuysMonteSS

Royal Smart Person
May 21, 2011
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Ethanol in the gas ??
Guy
 
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