No power, runs rough when shifted into drive

Tiny
PJDSEA
  • MEMBER
  • 1975 DODGE TRUCK
  • 5.2L
  • V8
  • 4WD
  • AUTOMATIC
  • 88,000 MILES
First, I cannot seem to get my idle to the 800 rpm that is my base. Otherwise it idles like a champ. However, when I drop it into drive it bogs down and runs rough, struggling to get going. I am able to kind of feather the throttle and get up to 50 mph or so, but if I give it solid throttle it lurch and falls on its face. I have good vacuum and solid, even compression on all cylinders. My truck has a w/318 automatic transmission and a two barrel carter bbd.
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Wednesday, June 29th, 2016 AT 10:07 PM

10 Replies

Tiny
CARADIODOC
  • EXPERT
Is the idle speed too high or too low? It sounds like you are describing a vacuum leak. You wont get any fuel to go with the air that sneaks in past the carburetor. The idle speed will be too high but without a corresponding increase in power. I would start by pinching off the vacuum hoses. Next, if you have an EGR valve, that could be sticking open due to carbon particles. Loosen it and stick a metal shim in there to block the port. If the running problem clears up, clean that valve or replace it.
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Wednesday, June 29th, 2016 AT 10:17 PM
Tiny
PJDSEA
  • MEMBER
Thanks for your reply. The idle speed is too high and when I attempt to turn the curb idle or fast idle screws down it dies at a certain point.
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Wednesday, June 29th, 2016 AT 10:52 PM
Tiny
PJDSEA
  • MEMBER
Also, the idle mixture screws have little to no effect on rpm's or vacuum. Thanks again.
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Wednesday, June 29th, 2016 AT 10:53 PM
Tiny
CARADIODOC
  • EXPERT
Dandy. Look for the vacuum leak. Pinch hoses, or spray water over the engine while it is still cold to see where it gets sucked in or where it makes the engine slow down momentarily. Spray water on the carburetor's throttle shaft bushings and its base gasket. That gasket is about 3/8" thick. There are small channels cut into the base of the carburetor and it does not take much for the gasket to deteriorate and leak. Obviously be sure there is no vacuum ports on the side of the carburetor that are not plugged or being used. I used to race 318s and 340s, and I always had custom projects. That means every car had at least one port plugged off with a short piece of hose and a drill bit. You need drill bits to go fast!

What state are you in that you still have a 1975 on the road? I am searching for a rust-free 1988 Grand Caravan with 15" wheels to replace my rusty trusty van.
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Wednesday, June 29th, 2016 AT 11:28 PM
Tiny
PJDSEA
  • MEMBER
I am in Washington State, Seattle to be exact. We do not get too much snow here so no salt.
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Wednesday, June 29th, 2016 AT 11:32 PM
Tiny
PJDSEA
  • MEMBER
I will investigate the possibility of a leak. Thank you again for your help.
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Wednesday, June 29th, 2016 AT 11:35 PM
Tiny
CARADIODOC
  • EXPERT
Holy cow. I am in the middle of Wisconsin. My best friend's son has been working for Boeing in Seattle for about five years!
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Wednesday, June 29th, 2016 AT 11:45 PM
Tiny
PJDSEA
  • MEMBER
Well, I hope he is liking it here as he is a long way from home. Lol.
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Wednesday, June 29th, 2016 AT 11:48 PM
Tiny
JACOBANDNICKOLAS
  • EXPERT
Since there is no power, are you sure there is no obstruction in the exhaust?
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Thursday, June 30th, 2016 AT 7:37 PM
Tiny
JACOBANDNICKOLAS
  • EXPERT
One other thought. Since it fails to accelerate quickly, are you certain that the accelerator pump is working properly? Ignition timing?
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Thursday, June 30th, 2016 AT 7:38 PM

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