Spark Port 2150
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New User
Joined: Mar 2008
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Spark Port 2150
Can anyone tell me why I have vacuum ,at idle, for the distributor vacuum advance from the spark port on my motorcraft 2150? I have it hook up just like the diagram shows, on the front driver corner of the carb (just in front of the throttle linkage). but Ia m getting vacuum at idle, and it just doesn't want to rev on the uppper end. Low end runs great. Vacuum gauge reads normal engine with this hooked up.
This is on a 1980 F250 with a 351M and 2150 carb. All stock.
Any information would be greatly appreciated!
This is on a 1980 F250 with a 351M and 2150 carb. All stock.
Any information would be greatly appreciated!
MSEE
Joined: Apr 2004
Posts: 10,386
Likes: 35
From: Austin, TX
The spark port has ported vacuum, also called timed vacuum. It sources vacuum above the throttle plates, as opposed to manifold vacuum which is vacuum at the actual manifold and hence is below the throttle plates. Ported vacuum is zero at idle and then goes up as you get on the gas, because it equals out to manifold vacuum. As you approach WOT both decrease.
It is hooked up this way so that the distributor does not advance the timing at idle, but advances the timing as you step on the throttle.
If you are getting a significant vacuum signal on the ported vacuum port at idle, your idle is too high.
It is hooked up this way so that the distributor does not advance the timing at idle, but advances the timing as you step on the throttle.
If you are getting a significant vacuum signal on the ported vacuum port at idle, your idle is too high.
Posting Guru
Joined: Oct 2005
Posts: 1,017
Likes: 3
From: Longwood, Fl
Water temp
One other remote possibility---
I dont recall if those engines had the 3 port sensor on a water jacket somewhere. The W motors had it on the intake thermostat housing. If you have the intake vacuum on the wrong port or the sensor is stuck, you could be feeding full vacuum to the dist at idle. Has anyone been messing with any vacuum hoses? Someone else will have to chime in if it dosnt have that sensor.
I dont recall if those engines had the 3 port sensor on a water jacket somewhere. The W motors had it on the intake thermostat housing. If you have the intake vacuum on the wrong port or the sensor is stuck, you could be feeding full vacuum to the dist at idle. Has anyone been messing with any vacuum hoses? Someone else will have to chime in if it dosnt have that sensor.
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