'81 GMC truck timing off


Old 09-16-02, 07:23 PM
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Question '81 GMC truck timing off

I have a 1981 GMC pickup auto matic with a 305 in it.I had some problems with it and thought it was the timing chain but it wasn't.
It ended up being the ignition module and while I was at it replaced the coil,rotor and suppressor.
But when I was able to get it back running the timing is way off.When I start it it idles extremely high and yet sometimes after it runs for awhile it will then idle so low that it won't stay running.But here lately it just runs very high the whole time.
I know it may be difficlut to explain but can someone help me set the time on it?
Any help is appreciated and my compliments on a great forum.
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Old 09-16-02, 09:29 PM
Join Date: Dec 2001
Posts: 2,538
to set ignition timing you will need a timing light and you will need to set it when it is idling at low rpm, you start engine unplug vacum line going to vacum advance the factory timing indicator for the 305 is located directly below water pump so you look directly behind the waterpump down to the balancer to see where your timing is at, sometimes the indicator will be missing or have the wrong one installed, timing should call for about 4 degrees btdc but should say on the underhood sticker the deep v in the indicator is 0 with your distributer a little loose you turn it counterclockwise to advance it or clockwise to retard it, set to spec, and retighten distributer, you say it idles high is your choke coming all the way off?
sometimes the fast idle cam will stick causing a fast idle. so your problem may be a carb problem instead of timing.
Old 09-17-02, 05:54 AM
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I appreciate it the timely response. Have a good one.

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