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1973 - 1979 F-100 & Larger F-Series Trucks
...strange problem.

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...strange problem.

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Old

Aug 9, 2012 | 11:20 PM

#1

PatientZero

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Freshman User

Joined: Jun 2012

Posts: 39

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...strange problem.

Okay. I'm working on my 1978 f100 with a 300. Auto transmission and original Carter yf. Carb. Truck runs like a dream in park or neutral, but as soon as put into gear, it idles way too low and backfires through the Carb when given gas. I've replaced plugs, wires, coil. Rebuilt carb and changed manifold gaskets. Adjusting timing doesn't seem to be helping any. Does anybody have any ideas about what i may be missing?
-patientzero

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Old

Aug 9, 2012 | 11:24 PM

#2

devino246

Post Fiend

Joined: Mar 2011

Posts: 8,501

Likes: 4

From: Lynchburg, VA

Start checking all your vacuum lines. Sounds like a vacuum leak.

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Old

Aug 10, 2012 | 07:13 AM

#3

fmc400

MSEE

Joined: Apr 2004

Posts: 10,386

Likes: 35

From: Austin, TX

Club FTE Gold Member

Agreed, sounds like a vacuum leak. I'm also going to assume that when you adusted the timing, you used a light and NOT by ear.

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Old

Aug 10, 2012 | 10:46 AM

#4

Rusty_Old_F250

Fleet Mechanic

Joined: Aug 2009

Posts: 1,771

Likes: 9

From: Western Washington

Check your booster, get a pair of vice grips and use them to clamp them onto the vacuum line for the booster then test drive it.

Sam

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