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Old 03-11-2009, 12:06 AM   #1
OregonC20
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Why?

Why is my truck running a bit rough after I drive it for more than 45 minutes plus?
When is cold it it drives fine, no problem. What can it be?

Thank you in advanced!
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Old 03-11-2009, 02:34 AM   #2
3quartertime
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Re: Why?

Choke is giving it more gas. Maybe it is running lean at operating temp...
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Old 03-11-2009, 08:57 AM   #3
68gmsee
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Re: Why?

I'd guess the choke also, except that it shouldnt take 45 minutes to warm up. But, it could be running too rich or have a vacuum leak somewhere.

I'd start with filters and fuel delivery and make sure it's not running rich (usually dark gray smoke). Then all ignition components like points, plugs, coil, distributor (cap and rotor), plug wires, etc.
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Old 03-11-2009, 11:15 AM   #4
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Re: Why?

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Sounds like the choke may not be opening up all the way. It wouldn't be a problem until the engine warms up good. After you drive it for a while take the air cleaner off and see if the choke plate is open all the way. (should be straight up & down) I would also pull one of the plugs out and see if it is sooted up. (black on end) If the choke is opening all the way but the plug is sooted up I would suspect a problem with the carb. (running rich)

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Old 03-11-2009, 01:36 PM   #5
mrein3
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Re: Why?

On older vehicles the choke is operated with a bi-metalic strip that was heated up by exhaust flowing across a passage in the intake. After you think the truck is warmed up feel the 'hump' on the intake that the choke is mounted to. If it is not hot, that passage is plugged. If plugged, the fix is to pull the intake and knock out the carbon.
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