Engine Won't Idle

[bischof]

I've had a hard time getting out to the last for a couple years, so I have some elderly gas in my tank (althought I keep it full to minimize condensation).

On my 1st outing of this year, my 1995 OMC Cobra 5.0L (model 502APHU) with Holley 2Bbl carburetor was working great for a couple hours, then went into a few minutes of very rough idling, then refused to run anywhere near idle.

I have to start it in neutral at 1/2 - full throttle, but I can't back it down to idle to put it in gear. It just dies near idle.

I know next to nothing about engines, but I would like to get started learning.
It seems there are a number of different things I could investigate, tear apart, and rebuild. Since I have semi limited time and don't want to rebuild a (possibly) perfectly good carburetor, I'm asking for easy, quick, and or high-probability suggestions.

 

[Bondo]

Re: Engine Won't Idle

I've had a hard time getting out to the last for a couple years, so I have some elderly gas in my tank (althought I keep it full to minimize condensation).

On my 1st outing of this year, my 1995 OMC Cobra 5.0L (model 502APHU) with Holley 2Bbl carburetor was working great for a couple hours, then went into a few minutes of very rough idling, then refused to run anywhere near idle.

I have to start it in neutral at 1/2 - full throttle, but I can't back it down to idle to put it in gear. It just dies near idle.

I know next to nothing about engines, but I would like to get started learning.
It seems there are a number of different things I could investigate, tear apart, and rebuild. Since I have semi limited time and don't want to rebuild a (possibly) perfectly good carburetor, I'm asking for easy, quick, and or high-probability suggestions.

Ayuh,.... I'd start by checkin' the Contents of the fuel filter, for anything other than Fuel,...
Also Sniff Test it to see if it still Smells like gasoline,....

After that, I'd dig into the Carb,...

 

[Gangly]

Re: Engine Won't Idle

I'd start by checking your idle screw. They do back out on occasion and need some adjustment. I need to adjust mine atleast once a year so check that first.

Second, like mentioned above, check your fuel filter and check your fuel screen where the fuel line taps into the carb.

 

[Boomyal]

Re: Engine Won't Idle

...also check to be sure that the venturis are not soaking wet down near idle. That Holley 2 bbl has a power valve that can rupture and it will flood the engine at low rpms.

 

[Silvertip]

Re: Engine Won't Idle

Idle speed and Idle mixture are two very different adjustments. Just make sure you know which one is which and that you understand what you are doing before you start "fiddling" with things and making it worse. Your original post made it sound like the fuel you had was "very" old. You might want to rig up a portable tank with some fresh fuel and see if the engine begins to run decent again. If it does, then you need to get rid of the old fuel.