E350 460 motor home vacuum problem
#1
E350 460 motor home vacuum problem
I have a 1987 Ford motor home with a 460 carburetor engine and Dura Spark ignition. I cannot hook up the vacuum advance line without the engine popping through the carb and stalling. Here is what I have done so far:
• Just rebuilt Autolite holly carb
• New pick up module
• New cap
• New rotor
• New wires
• New coil
• New plugs
• New ignition module
• New adjustable vacuum canister.
• I set the timing 8° before the dead center at 650 rpm with the vacuum line off and plugged.
• I locked the distributor bolt tight.
• I checked the timing marks with a timing light to see if the mechanical advance is working. At about 2500 rpm it advances about 25° - 30°, so that seems okay.
• I tried direct vacuum and ported vacuum
• As soon as vacuum reaches the canister the engine won’t run and pops through the carb. I was told it could be off a tooth on the distributor gear, so I moved it one tooth and it didn’t make a difference. I turned the adjustment Allen screw in the vacuum canister all the way in and tested it with a vacuum pump and it is stopping the travel as it should.
With the vacuum line disconnected it seems to idle smoothly and on the road is okay, too. But it uses more fuel and there is some loss of power.
Any ideas about what is going on?
Going Nuts With This
• Just rebuilt Autolite holly carb
• New pick up module
• New cap
• New rotor
• New wires
• New coil
• New plugs
• New ignition module
• New adjustable vacuum canister.
• I set the timing 8° before the dead center at 650 rpm with the vacuum line off and plugged.
• I locked the distributor bolt tight.
• I checked the timing marks with a timing light to see if the mechanical advance is working. At about 2500 rpm it advances about 25° - 30°, so that seems okay.
• I tried direct vacuum and ported vacuum
• As soon as vacuum reaches the canister the engine won’t run and pops through the carb. I was told it could be off a tooth on the distributor gear, so I moved it one tooth and it didn’t make a difference. I turned the adjustment Allen screw in the vacuum canister all the way in and tested it with a vacuum pump and it is stopping the travel as it should.
With the vacuum line disconnected it seems to idle smoothly and on the road is okay, too. But it uses more fuel and there is some loss of power.
Any ideas about what is going on?
Going Nuts With This
#2
#3
#4
Vacuum Advance
Yes, it could. If the wiring problem only occurred when the vacuum canister moves the advance plate. Also a loose or damaged advance plate, improperly mounted pickup coil, or a coil gap that changes when advanced.
#5
Thanks for the info, Jack. You were right on. It was a defective NEW pick up module. I put about 100 miles on it this past week and it ran pretty good, but still seems to be holding back climbing hills. I may have to mess with the new vacuum advance adjustable canister. The original was not adjustable.
Tom
Tom
#6
Tom FWIW I went through a spate of bad GM distributor modules, bought new from NAPA a few years ago---their Silverline of parts newly introduced in the middle 90's. Saved a good 50% over the good stuff, after two of those flamed out within 100 driving miles it was time to go back to the better quality.
Sometimes these parts have a run of bad ones---frustrating to be sure.
Anyway glad you've got this mostly sorted out---feels good having a trouble-free van once again.
Sometimes these parts have a run of bad ones---frustrating to be sure.
Anyway glad you've got this mostly sorted out---feels good having a trouble-free van once again.
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