Vacuum advance
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Mountain Pass
Joined: Apr 2015
Posts: 126
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Vacuum advance
Im getting my truck ready to get smogged (79 F350 4x4) And the 460 in it is a 1987 year model , dont' know what it's out of just 87.
I have the initial timing set at 11 degrees btdc with the vacuum hose unhooked and pluged now when I plug the vac hose back on the distributor my timing jumps to 34 degrees, both taken at idle. The vacuum hose goes from the dist. to the bottom outlet on the heat switch on the thermostat housing with the top 2 outlets meeting at a Y and then to a manifold vacuum tree. The ported vacuum on the carb goes to another heat switch on the T housing then to the EGR valve. All these vacuum hoses look like they have been where they belong for a long time. Anyway I have 11 initial degrees advance without vacuum and 34 degrees with vacuum AT IDLE. this don't seem right ??????????
Gene
I have the initial timing set at 11 degrees btdc with the vacuum hose unhooked and pluged now when I plug the vac hose back on the distributor my timing jumps to 34 degrees, both taken at idle. The vacuum hose goes from the dist. to the bottom outlet on the heat switch on the thermostat housing with the top 2 outlets meeting at a Y and then to a manifold vacuum tree. The ported vacuum on the carb goes to another heat switch on the T housing then to the EGR valve. All these vacuum hoses look like they have been where they belong for a long time. Anyway I have 11 initial degrees advance without vacuum and 34 degrees with vacuum AT IDLE. this don't seem right ??????????
Gene
Postmaster
Joined: Mar 2011
Posts: 2,698
Likes: 7
From: Taxachusetts
You're correct.... it's not right. Obviously, and as you know, your distributor's vacuum advance is hooked to manifold vacuum. Should be to ported.
Vacuum routing on your '87 engine would be Sanskrit to me. Sorry.
Vacuum routing on your '87 engine would be Sanskrit to me. Sorry.
Laughing Gas
Joined: May 2006
Posts: 1,140
Likes: 13
From: Port Orchard Wa
I'll try not to start a fire storm about manifold vs ported. But your truck is working as intended. It is not a street racer. That advance at idle was developed to increase fuel efficiency and reduce emissions, so I would not mess with it if your trying to smog in CA. Suggest you read this for more detailed understanding https://www.fordmuscle.com/archives/2000/03/timing/
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