[yberther]

I recently got the '83 Z28 running after 9 years of sitting. It was running fine other than a slightly rough idle and suddenly after changing the spark plugs, to pre-gaped plugs, the car ran fine. It hadn't been driven around because of a broken/hanging transmission mount, but suddenly after removing the AC pump (no belt was previously attached) the car wouldn't run. It started popping really deep, and smoke poofed out of the headers. After trying a couple of times, the car started to backfire (smoke and sometimes flames) out of the carbs. Is this a timing issue? Is a valve stuck open? Fuel problem (9year old fuel)?? How can I fix this

 

[dale68z]

Very real possibility the old gas caused the valve to stick. I have fixed this before by usig gm top engine cleaner.
Most likely will need to remove the valve springs to free up the valve. Once they are freed up, start the engine and run the top eng. cleaner through the carb to clean the guides, and stems. May be able to free them up by just dumping some down the carb with the engine running, shutting it off and letting it soak for an hour or 2.

 

[yberther]

But the old gas hadn't been doing anything before...
Like I ran it for 5 min with old oil and an oil additive
then changed the oil and ran it for probably a total of 30 min over 2 days
then ran it today for 5 min backing it out of the garage, then suddenly it stopped

 

[dale68z]

I have had it happen twice to customers cars, ran the engine with old gas,until they were completely warmed up, both ran well. Let the engine completely cool down, and crap, it wont run, 1 car had bent valves, the other bent pushrods (dont know if the valves bent). Now when a stored car comes in, they get ran for a while with fresh gas, and get the cleaner dumped in the carb before we shut them off.
Only way to know for sure at this time is to pull the valve covers. Check for loose rocker arms, if it's loose, you found your valve.

 

[blue ss]

Are you sure you didnt knock off a vacume hose or plug wire while removing the a/c. Mabe a dry rotted hose somewhere, try leaving the choke plate closed up to simulate rich mix. If its real bad you should be able to hear the leak. Do you hear any engine noise rockers or metal noise?

 

[yberther]

there was one hose that was knocked off of a filter looking thing (smelled like it had fuel) but I'm not really sure what it was. A friend told me it was an air filter, it was super rusted and just broke off...
There was a really loud knocking, not sure if it was metal though...
Possibly that the exhuast is blocked or something was a suggestion from an uncle....so I don't know