Vacuum advance question
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Freshman User
Joined: Jul 2002
Posts: 48
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Vacuum advance question
I recently bought a 78 F 150 with a 351m in it. It's an amazing motor considering it's got 200,000 miles of abuse and neglect and it still runs fairly strong! I am sorting out small problems with it and need help. Question: the vacuum advance mechanism on the distributor has a single line from the radiator hose goose neck switch on the motor leading to the front of the adv. mech.. There is a hole on the top back of the mech. nearest the distributor. I suspect there was a second hose there at one time to help retard the spark but the tube snapped off and someone tossed the line in the weeds. If my suspicions are right where did this second hose get it's vacuum from. I,m getting slight spark knock and think maybe this is the cause. Can anyone help?
Lead Driver
Joined: Nov 2000
Posts: 6,651
Likes: 352
From: Albuquerque
Vacuum advance question
If you are getting spark knock out of a stock 351m I suspect you have way too much timing. I think the answer would be to connect the dist. advance to full vacuum and run about 12 degrees initial. You can play around with the initial. Make sure the vacuum adv. is functioning.
Lead Driver
Joined: Nov 2000
Posts: 6,651
Likes: 352
From: Albuquerque
Vacuum advance question
Good question. I've heard some had two inlets/advance thingies maybe for decel or something. If you have only one hose connection on the distributor I'd just go straight with it. With age a lot of those older emmissions swithces etc. don't work right anyway.
