Help! 1981 F150 4.9 Liter idling rough/not at all
#1
01-31-2011, 12:31 PM
Join Date: Jan 2011
Location: CYPRESS, TX
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Help! 1981 F150 4.9 Liter idling rough/not at all
Hi All,
Been lurking for awhile, but now I seek answers, advice, etc.
I have a 1981 F150 with the 300 ci 4.9 liter inline six that I bought off a guy for $600 bucks. I have been driving it for the last 4 months. It has/had a couple leaks, so about three weeks ago I decided to start replacing gaskets on it.
I have replaced the head gasket, intake, exhaust, valve cover, oil pan, etc.
I got it all back together, it turns over, but as soon as I let off the gas it dies. If I stay on the gas it runs, but extremely rough I got together with my stepdad and he is thinking it's the carb. I have ordered a rebuild kit and plan on doing that later this week, but I wanted to see what the "experts" had to say. I have never done anything this extensive and will gladly take and advice or words of wisom.
I have a sneaking suspicion the rear tank is sucking fuel back from the motor, but really don't know how to diagnose it. Also my exhaust is blowing out tiny specs of burnt oil, that I think is left over from the previous oil leak, but honestly I don't know.
Timing seems to be fine, as when I rev it up higher it runs a little smoother. All spark plugs are getting spark.
Any how, any thoughts? Answers? I am not a mechanic by any means, so I may have trouble explaining or understanding some of the technical terms, so please bear with me.
Thanks for any help!
-Casey
Been lurking for awhile, but now I seek answers, advice, etc.
I have a 1981 F150 with the 300 ci 4.9 liter inline six that I bought off a guy for $600 bucks. I have been driving it for the last 4 months. It has/had a couple leaks, so about three weeks ago I decided to start replacing gaskets on it.
I have replaced the head gasket, intake, exhaust, valve cover, oil pan, etc.
I got it all back together, it turns over, but as soon as I let off the gas it dies. If I stay on the gas it runs, but extremely rough I got together with my stepdad and he is thinking it's the carb. I have ordered a rebuild kit and plan on doing that later this week, but I wanted to see what the "experts" had to say. I have never done anything this extensive and will gladly take and advice or words of wisom.
I have a sneaking suspicion the rear tank is sucking fuel back from the motor, but really don't know how to diagnose it. Also my exhaust is blowing out tiny specs of burnt oil, that I think is left over from the previous oil leak, but honestly I don't know.
Timing seems to be fine, as when I rev it up higher it runs a little smoother. All spark plugs are getting spark.
Any how, any thoughts? Answers? I am not a mechanic by any means, so I may have trouble explaining or understanding some of the technical terms, so please bear with me.
Thanks for any help!
-Casey
#2
02-01-2011, 11:23 AM
Well, the best advice is: EFI!!! 
But in the meantime...
Rebuilding the carb is probably less "extensive" than replacing the head gasket, but both require a lot of attention-to-detail. The rebuild kit should come with very detailed instructions, so follow them religiously. But it's probably not worth the effort. Did you check the prices of rebuilt carbs from your local parts stores? Getting one already set up will save you a LOT of time & headache, but you have to get a good one. Don't buy the cheapest one from the zone - spend a couple of extra bucks to get a name-brand (Carter, Holley, etc.) from NAPA, CarQuest, Parts+Plus, All-Pro, or at worst: Advance/O'Reilly.
No, the tank can't pull gas - it would collapse long before it had any effect on the carburetor.
That's not oil coming out of the exhaust - it's soot (from the engine running rich occasionally) and water (from normal combustion).
If you have any problems with terminology, click this:
Automotive Terms & Abbreviations
But in the meantime...
Rebuilding the carb is probably less "extensive" than replacing the head gasket, but both require a lot of attention-to-detail. The rebuild kit should come with very detailed instructions, so follow them religiously. But it's probably not worth the effort. Did you check the prices of rebuilt carbs from your local parts stores? Getting one already set up will save you a LOT of time & headache, but you have to get a good one. Don't buy the cheapest one from the zone - spend a couple of extra bucks to get a name-brand (Carter, Holley, etc.) from NAPA, CarQuest, Parts+Plus, All-Pro, or at worst: Advance/O'Reilly.
No, the tank can't pull gas - it would collapse long before it had any effect on the carburetor.
That's not oil coming out of the exhaust - it's soot (from the engine running rich occasionally) and water (from normal combustion).
If you have any problems with terminology, click this:
Automotive Terms & Abbreviations