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engine surge, varying idle

mike82

Well-known member
Joined
May 21, 2006
Messages
116
Location
Claremore,Okla.
Corvette
L82 Pace
this weekend the q-jet was rebuilt. i also installed new plugs ,plug wires cap,rotor and ign. module. i fired up the motor yesterday and for the first couple of minutes it ran fine, but soon after the motor began to surge above idle then drop down below idle(approx. a couple hundred rpm above idle to a couple of hundred below idle). i thought maybe some dirt had gotten into carb so i took it apart and cleaned it again(yes,. i did use a rebuid kit), but had the same result. this surge and drop in idle would happen a couple of times consecutively every 3-5 minutes. if i put the slightest pressure on the gas pedal the motor would smooth out without hesitation at the pedal. i was thinkin' maybe the fuel pump was going bad. the car is a '78 but has only 23,XXX miles on it. any advice would be greatly appreciated.....thanks,,,,mike.
 

mike82

Well-known member
Joined
May 21, 2006
Messages
116
Location
Claremore,Okla.
Corvette
L82 Pace
i've been searchin for a leak(s). just a little while ago i checked EGR valve and noticed the two nuts holding it down were only finger tight, plus the gasket was partially gone. i replaced gaskets thinkin i repaired the problem but once the motor got up to temp, it fouled up again. ;shrug :mad :bash :puke
 
Joined
Apr 29, 2001
Messages
2,141
Location
Rio Rancho, NM
Corvette
1981 HD Suspension; ZN1 Option
Mike,

What jumps at me is the fact that you had the carb reworked. Usually, the carb shop can't set it to your car specs, for the carb set-up was used on so many models.

Send me an e-mail, and when I get home, I send you the Rochester manual (let me know if you have limits on the attachment size you can receive with your internet provider).

I have posted some of the pages for the tuning manual (AC Delco SD-100A) on the member's galleries. Page 39 explains how to adjust the air valve for air valve with no "letter" on the adjusting screw [procedure "A"], and for "lettered" air valves [procedure "B"].

Here is an example...

ACDELCO_SD-100A_page_139_copy.JPG


ACDELCO_SD-100A_page_140_copy.JPG


Anyway, assuming that all of your air hoses are connected, and no air leaks are present, then I would suggest to check your carb to make sure are on square one. Once you know that the carb set-up correctly, then you'll be able to really tell whether there is something wrong with the rebuild.
 

smithjw

Well-known member
Joined
Apr 3, 2003
Messages
71
Location
Modena, New York
Corvette
1981 red
I tend to agree that if the problem started after the rebuild, then that would be suspect. However, your symptoms are very similar to ones that I have had in the past and it did turn out to be a bad fuel pump.
 

daveintexas

Active member
Joined
May 3, 2006
Messages
44
Location
San Antonio,TX
Corvette
1974 454 Stingray
did you check to make sure the base gasket was the same as the old one? also, the easiest way to check for a vaccum leak, is to take some carb cleaner and use the small tube to pinpoint the spray. Spary it arond the base of the carb, and the egr valve, and along the intake manifold.If you have a leak, you will notice the change in the way it runs right away.Hope this helps.;shrug
 

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