Vacuum advance problems
Freshman User
Joined: Aug 2001
Posts: 43
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From: usa
Vacuum advance problems
I recently put in a stock 351m in a 78 f-150 4wd. I installed a set of headers and put in an summit double roller timing set with "0" advance. I removed all smog and put a spacer under the factory 2 barrel carb. This thing will smoke the BFG mud t/a 35's as long as you stay on the gas with 4.11 gears and posi. The only problem I have is I can not hook up the vacuum advance hose on the distributor without it missing real bad. Disconnected it runs great. I tried to putting it on every fitting on the carb and intake that the hose will fit on and it starts missing when I give it any gas. With the vac. advance hooked to the carb. i put the timing light on it is about 4 deg. at idle and goes to about 8 deg. when i give it gas, but starts to miss. The vac. advance on the distributor seems to be working fine. I know it needs to be hooked up. This is the original dist. and did not do this in the 78 T-bird i pulled it out of. Does anyone have any suggestions?
Posting Guru
Joined: Aug 2000
Posts: 1,984
Likes: 2
Vacuum advance problems
150, if this is an original Motorcraft 2150 carb, the vacuum advance port is the one on the passenger side, under the choke mechanism. It should have no vacuum at idle, then a vacuum increase when the throttle is opened. The initial timing with the vacuum hose to dist disconnected (and plugged) should be about 4 deg BTDC, or maybe a little more. Set it up this way, and see if it still misses.
Luck,
Don
Luck,
Don
Postmaster
Joined: Aug 2001
Posts: 4,270
Likes: 5
From: Delaware
Vacuum advance problems
Check for bare wires or foreign material under the cap around the breaker plate. This could be shorting out when the vacuum advances the breaker plate. Also look for material or tracks inside the Cap or on the rotor which can cause arcing when the spark occurs earlier.
Dan Lee
Dan Lee
Moderator
Joined: Jan 2001
Posts: 56,992
Likes: 2,741
From: Virginia
Vacuum advance problems
It doesn't sound like the initial timing is too far advanced, so I would investigate what danlee said about the plate moving in the dist. Maybe one of the wires is broken internally and when the plate moves, it gives a bad connection.
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