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Old 07-29-2017, 10:44 AM   #1
Noswal
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Default Vacuum advance/MSD problems

I have a 1978 F100 with a 351w. Kept having problems with the DuraSpark ignition box so I replaced it with a used MSD 6A ignition box and kept the duraspark distributor. When I plugged in the vacuum advance the engine will not accelerate without popping and losing power. I thought that I might have a bad vacuum advance so I replaced it. No change. I replaced the entire distributor. No change. The guy I got the box from said he only ran it a little while on his 4 cylinder import.
Anybody else have any probems like this with the msd box. Is there advance built into the box? Maybe I just have a bad box, but it sure is frustrating.
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Old 07-29-2017, 11:22 AM   #2
dmsfrr
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Default Re: Vacuum advance/MSD problems

Is there vacuum at the end of the vac hose that connects to the distributor?
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Old 07-29-2017, 12:19 PM   #3
Noswal
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Default Re: Vacuum advance/MSD problems

There is vacuum at the carburetor. this has me baffled. I think I'll chnge the MSD and see what happens.
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Old 07-29-2017, 05:16 PM   #4
JeffB2
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Default Re: Vacuum advance/MSD problems

Call MSD Tech ? Possible 4 cyl to 8 cyl issue.
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Old 07-29-2017, 06:10 PM   #5
miker98038
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Default Re: Vacuum advance/MSD problems

On the common 6 series MSD. Page 5, loops for 8-6-4 cylinder operations. Jeff hit it right on.

https://www.jegs.com/InstallationIns...1/121-6425.pdf
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Old 07-30-2017, 08:32 AM   #6
Noswal
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Default Re: Vacuum advance/MSD problems

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I did call the MSD tech and his suggestion was to run the truck without the vacuum advance connected. Not much help. None of the loops are cut. It does run reasonably well without the vacuum advance, but I would like to resolve the issue and connect it.Thanks for everybodys comments and help.
Butch
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Old 07-30-2017, 06:06 PM   #7
JeffB2
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Default Re: Vacuum advance/MSD problems

[QUOTE=miker98038;1506264]On the common 6 series MSD. Page 5, loops for 8-6-4 cylinder operations. Jeff hit
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Old 07-30-2017, 10:32 PM   #8
cousinjd
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Default Re: Vacuum advance/MSD problems

Is the vacuum constant or just when you crack the throttle?
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Old 07-31-2017, 07:35 AM   #9
Noswal
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Default Re: Vacuum advance/MSD problems

Cousinjd,
Seems to idle ok, but when its throttled up it misses and pops like its 180* out of time.
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Old 07-31-2017, 07:57 AM   #10
Sanddoc
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Default Re: Vacuum advance/MSD problems

Ok, I know I'm not answering your problem directly, but I think there is a setting
on the 6 for 4, 6, 8
Here is what I did with the Duraspark, which although can work fine, has way to
many wire.. OK, plug your ears, Die hard Ford guys, (which I am)
I used the GM control module to fire the Dizzy
It is a very easy swap, they cost around $10 on Ebay (get American made) units
4 wires and your hooked up. Carry an extra one in your clove box.
I had it on my 351C and now on my 74 Dart 318..
Best
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Old 07-31-2017, 11:33 PM   #11
craig
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Default Re: Vacuum advance/MSD problems

Sandoc is right. I have a GM module firing a Chinese wantabe msd dist. in my flathead, my old 460 1 ton with the duraspark dist. and an old 360 Dodge pickup. The things work well if you (1) keep them cool, so mount them on some kind of a heat sink, even a piece of scrap plate will work (2) they like lots of power, so use a 12 gauge feed wire, full voltage, no ballast resistor. Treat them right and they work forever.
It's amazing how guys will run out and buy the latest and greatest aftermarket stuff just because of the flashy box and high price...it's gotta be better cuz it cost more, right? and besides all the big name racers use them....
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