issues starting and rough idle
FTE Legend
Joined: Jul 2010
Posts: 32,875
Likes: 48
From: Northeast, OK
So, I guess I'm lost. It runs fine hot, which says the basic carb and ignition system are fine. But it doesn't run well cold, which just takes a richer mix, and that's done with the choke - which you control. Where's the problem? 
Moderator
Joined: Nov 2007
Posts: 22,415
Likes: 92
From: Denver Metro Area, CO
Did you not see the devil-face smiley at the end of his comment? Do you know what those things mean?
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Junior User
Joined: Aug 2013
Posts: 63
Likes: 0
From: WI
No, I didn't see it. where's the most common place for a vacuum leak?
Fleet Mechanic
Joined: Sep 2013
Posts: 1,504
Likes: 8
From: Indian Falls, New York
The could be anywhere really. Best thing I can think of is just go around and check everything with a fine tooth comb. Vacuum leaks can be a bitch to find.
Lead Driver
Joined: Jul 2009
Posts: 6,477
Likes: 19
From: Sheffield, AL
Source of potential vacuum leaks for 4.9L engine:
The two hold down bolts at the carburetor base being loose, the PCV valve hose, the vacuum line which goes to the power brake booster [the booster, itself], vacuum lines which control the HVAC system, check all vacuum ports on the carburetor and vacuum tree, located on the intake manifold. One vacuum line goes to a splitter [distribution point] located on the firewall, to the passenger side. Also, the gaskets between the intake manifold and the engine block.
Perhaps, the intake gasket is leaking when the engine is cold and as it warms up and the metal expands, the sealing improves?
Keep reporting back and someone will come up with the answer.
Does your distributor have a vacuum hose going to it?
The two hold down bolts at the carburetor base being loose, the PCV valve hose, the vacuum line which goes to the power brake booster [the booster, itself], vacuum lines which control the HVAC system, check all vacuum ports on the carburetor and vacuum tree, located on the intake manifold. One vacuum line goes to a splitter [distribution point] located on the firewall, to the passenger side. Also, the gaskets between the intake manifold and the engine block.
Perhaps, the intake gasket is leaking when the engine is cold and as it warms up and the metal expands, the sealing improves?
Keep reporting back and someone will come up with the answer.
Does your distributor have a vacuum hose going to it?
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Junior User
Joined: Aug 2013
Posts: 63
Likes: 0
From: WI
I'll check on the distributor, I'm not sure that there is one, intacke gaskets were was replaced a few days ago, along with carb, I dint belive the bister line is leaking but I can recheck, the PVC, might not be sealing good on the top, ill. Try and find some carb cleaner to spray.
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Junior User
Joined: Aug 2013
Posts: 63
Likes: 0
From: WI
i have determined no vac leaks, Y? you may ask, because i believe i've found the culprit, i believe its only half converted to the duraspark2. it still has the computer controlled dist. so i did some looking on here in the threads on it,. i gotta go find a dist. out of a 80-83 and wiring and coil, and grey box and replace it with my setup and run the vacuum line. and if im correct this should fix it.
FTE Legend
Joined: Jul 2010
Posts: 32,875
Likes: 48
From: Northeast, OK
Then it won't run right cold or hot. It will be in limp-home mode and the timing will be locked at something like 10 degrees BTDC. No advance of any kind. Lousy performance and awful gas mileage. That has to be fixed before anything else.
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Junior User
Joined: Aug 2013
Posts: 63
Likes: 0
From: WI
well i hope that truck at the junk yard is 80-83, if not i gotta start finding other places to look, the junkyard on has 1 truck like mine.
FTE Legend
Joined: Jul 2010
Posts: 32,875
Likes: 48
From: Northeast, OK
The trucks with the same engine prior to 80 had DS-II. You just need a dizzy with a vacuum advance from a 300. The presence of the vacuum advance canister tells you it isn't computer controlled.
