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Old 02-26-2012, 09:52 PM
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Timing and vacum advance

Alright so i just bought a 84 gmc 2500 with a 350. when i got it and checked the timing and it was set at 13 degrees at idle stock specs are are 8 so i changed it to that. When i changed it to 8 it ran like crap. it would stall out and backfire through the carb like crazy. i stalled at a red light in the middle of the intersection!! so after that i changed it back to 13 but it still ran about the same. That whole time i did not know that you were supposed to disconnect the vacuum line going from the carb to the distributor. I am just wondering if that is why it still runs like crap? everywhere online says to disconnect it but i cannot find anywhere that says why. i would just like to know why i am supposed to disconnect it and if that is whats causing my problems. thanks

ps its a 350 that was supposedly bored out to 383. has 600 cfm edelbrock and edlebrock intake manifold. Also said the top end was rebuilt/upgraded.

i put in a new fuel filter, fuel pump, and also cleaned the carb and seafomed it. all that has helped a little but its still will stall out if i mash the gas at a redlight. it idles and revs fine under no load. i tried adjusting the mixture screws also. any advice would be appreciated as i am going crazy over this!!

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Old 02-26-2012, 10:29 PM
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Quote:
Originally Posted by Stormtrooper
Alright so i just bought a 84 gmc 2500 with a 350. when i got it and checked the timing and it was set at 13 degrees at idle stock specs are are 8 so i changed it to that. When i changed it to 8 it ran like crap. it would stall out and backfire through the carb like crazy. i stalled at a red light in the middle of the intersection!! so after that i changed it back to 13 but it still ran about the same. That whole time i did not know that you were supposed to disconnect the vacuum line going from the carb to the distributor. I am just wondering if that is why it still runs like crap? everywhere online says to disconnect it but i cannot find anywhere that says why. i would just like to know why i am supposed to disconnect it and if that is whats causing my problems. thanks

ps its a 350 that was supposedly bored out to 383. has 600 cfm edelbrock and edlebrock intake manifold. Also said the top end was rebuilt/upgraded.

i put in a new fuel filter, fuel pump, and also cleaned the carb and seafomed it. all that has helped a little but its still will stall out if i mash the gas at a redlight. it idles and revs fine under no load. i tried adjusting the mixture screws also. any advice would be appreciated as i am going crazy over this!!
You can run more initial timing than what the underhood sticker says most of the time, 12-14 degrees is OK as long as the total timing doesn't exceed 36-38 degrees.

You disconnect the vacuum advance to check and adjust the initial and total timing- but you have to hook it back up when you're done. If the vacuum advance is working the idle speed should increase when you hook it back up. If not check to see if it's N/G- it should retract the arm when a vacuum is applied by mouth and it should hold vacuum.
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Old 02-27-2012, 08:54 AM
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so is my timing way off now because i didnt disconect the advance line when we checked and readjusted the timing he first time? so if i recheck the timing and reset it with the vacuum line disconected and the hole plugged that could fix my problem?

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Old 02-27-2012, 09:01 AM
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Quote:
Originally Posted by Stormtrooper
so if i recheck the timing and reset it with the vacuum line disconected and the hole plugged that could fix my problem?

Thanks
Quite possibly. Remember to hook it back up after setting/checking the timing.

DETERMINING TDC will allow you to be sure the timing tab and damper are correctly indicating TDC.

MAKE A TIMING TAPE to see what the total timing is, w/o needing to use a dial back timing light. You can also buy a timing tape, get one that matches the diameter of your damper.

The image shows the correct orientation of the timing tape:


There were three different combinations of SBC damper lines and timing tabs used through the years that go together. THIS page describes them.
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