Vacuum drops in drive, help!!!
Thread Starter
|
Elder User
Joined: Apr 2004
Posts: 535
Likes: 0
From: Tucson, AZ
Vacuum drops in drive, help!!!
In park my 1973 w/ 300 and C4 pulls 17-18 in hg vacuum. As soon as I put it in drive it drops to 13-14 in hg and runs horrid. What could this be? Help!!!
Thread Starter
|
Elder User
Joined: Apr 2004
Posts: 535
Likes: 0
From: Tucson, AZ
Backing out the mixture screw, didn't help. Here's the full details.
1973 Ford F100
1985 300 Inline 6 Motor
1973 C4 Transmission
Compression
Cylinder 1-140, 2-145, 3-145, 4-145, 5-145, 6-145
Vacuum 17 in hg w/ occasional drop to 16 in hg (valve out of adjustment?)
New Points Distributor, Coil, Rotor, Condensor, Points, Cap, Wires, Plugs)
Timing - 6 degrees BTDC Dwell - 35-37 degrees Plug Gap- .035"
Has new carb, fuel pump, alternator, starter, motor mounts, radiator.
Vacuum routing is the same as it was one old engine and appears to be correct according to diagram.
Checked for vacuum leaks with propane torch and carb cleaner.
Don't know if the following would make a difference but just in case.
Has 1973 intake/exhaust manifolds.
1974 Carter Carb for 300 eng. w/ Electric choke.
1973 Ford F100
1985 300 Inline 6 Motor
1973 C4 Transmission
Compression
Cylinder 1-140, 2-145, 3-145, 4-145, 5-145, 6-145
Vacuum 17 in hg w/ occasional drop to 16 in hg (valve out of adjustment?)
New Points Distributor, Coil, Rotor, Condensor, Points, Cap, Wires, Plugs)
Timing - 6 degrees BTDC Dwell - 35-37 degrees Plug Gap- .035"
Has new carb, fuel pump, alternator, starter, motor mounts, radiator.
Vacuum routing is the same as it was one old engine and appears to be correct according to diagram.
Checked for vacuum leaks with propane torch and carb cleaner.
Don't know if the following would make a difference but just in case.
Has 1973 intake/exhaust manifolds.
1974 Carter Carb for 300 eng. w/ Electric choke.
Thread Starter
|
Elder User
Joined: Apr 2004
Posts: 535
Likes: 0
From: Tucson, AZ
I currently have autolite 45s which I've used for a long time, has anyone had a bad experience with them?
Trending Topics
Post Fiend
Joined: Jan 2003
Posts: 10,323
Likes: 2
From: Montana Territory
Autolite 45 is the correct plug, gap should be .034".
If it drops in drive its the modulator. To test it, try to put it in first gear, then second... if it doesn't drop, its the modulator... (I'm mostly certain of this, but its really late
) I'm pretty sure the C4 only uses the vacuum to shift in Drive, and not in the other gears...
If it drops in drive its the modulator. To test it, try to put it in first gear, then second... if it doesn't drop, its the modulator... (I'm mostly certain of this, but its really late
) I'm pretty sure the C4 only uses the vacuum to shift in Drive, and not in the other gears...
FTE Stories
Ford Trucks for Ford Truck Enthusiasts
Top 10 Most Expensive Ford Trucks Ever Sold on Bring a Trailer
Joe Kucinski
2027 Ford Super Duty Buyer's Guide (Every Model, Engine, & Package)
Brett Foote
Top 10 Ford Truck Tragedies
Joe Kucinski
AEV FXL Super Duty - the Super Duty Raptor Ford Doesn't Make
Brett Foote
Lobo Vs Lobo: Proof the F-150 Lobo Should Be Even Lower!
Michael S. Palmer
Ford's 2001 Explorer Sportsman Concept Looks For a New Home
Verdad Gallardo
10 Best Ford Truck Engines We Miss the Most!
Joe Kucinski
2026 Shelby F-150 Off-Road: Better Than a Raptor R?
Brett Foote
