Engine Question
Thread Starter
Cruising
Joined: Apr 2001
Posts: 11
Likes: 0
From: VA
Engine Question
I was wondering if anyone else has ever had this problem My 1973 Vette w/L82 runs smooth, idles smooth but at all speeds you can feel it lunging. It feels like you are pressing the gas on and off....kind of like varing the speed up and down up and down. You cant see anything on the speedometer (I mean its not losing speed). It is just driving me CRAZY. If anyone has heard of this please let me know what could be causing this.
Burning Brakes
Joined: Feb 2004
Posts: 958
Likes: 1
From: In the Beautiful Shenandoah Valley of VA
This can be casued by several things. Overadvanced ignition timing, lean fuel mixture, or an overactive (weak diaphragm spring) EGR valve can cause this. For a quick check on the EGR, simply remove and plug the vacuum hose temporarily and take it for a drive. I wouldn't suggest leaving it disconnected permanently though.
Steve
Steve
Thread Starter
Cruising
Joined: Apr 2001
Posts: 11
Likes: 0
From: VA
Originally Posted by page62
Kinda like surging? Have you checked the timing and the vacuum advance function?
Drifting
Joined: Nov 2002
Posts: 1,665
Likes: 1
From: Ontario
Originally Posted by Dale73
Yes, it's a surge that happens all all speeds. You do not feel it on acceleration. But it is felt say if you try to hold it at 55. The surge is very suddle feeling. Not bucking.
What is the difference with an engine accelerating and cruising - vacuum level... Accelerating (load) = low vacuum and cruise you have lots of vacuum. First check your vacuum advance & timing, vacuum leaks or EGR like has been mentioned.
how to set your timing for peak peformance by Lars
If you rule out all your timing & vacuum leaks then the carb is next. What carb do you have? Here are some carb links you may find usefull...
corvettefaq.com carb tuning links
Le Mans Master
Joined: Mar 2002
Posts: 7,456
Likes: 2
From: Coming home from Luckenbach Texas
I'm gonna quote Lars here: "...the car will chug and jerk at cruise from (an) over-advanced condition."
If that sounds, correct, check your timing (it can't hurt). And while you're in there, check your mechanical and vacuum advance systems for proper functioning. Download a copy of Lars timing paper from www.corvettefaq.com if you're not familiar with the technique we commonly use around here.
If that sounds, correct, check your timing (it can't hurt). And while you're in there, check your mechanical and vacuum advance systems for proper functioning. Download a copy of Lars timing paper from www.corvettefaq.com if you're not familiar with the technique we commonly use around here.
Le Mans Master
Joined: Apr 1999
Posts: 6,134
Likes: 46
From: Raleigh North Carolina
Originally Posted by Dale73
I was wondering if anyone else has ever had this problem My 1973 Vette w/L82 runs smooth, idles smooth but at all speeds you can feel it lunging. It feels like you are pressing the gas on and off....kind of like varing the speed up and down up and down. You cant see anything on the speedometer (I mean its not losing speed). It is just driving me CRAZY. If anyone has heard of this please let me know what could be causing this.
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Thread Starter
Cruising
Joined: Apr 2001
Posts: 11
Likes: 0
From: VA
Originally Posted by page62
I'm gonna quote Lars here: "...the car will chug and jerk at cruise from (an) over-advanced condition."
If that sounds, correct, check your timing (it can't hurt). And while you're in there, check your mechanical and vacuum advance systems for proper functioning. Download a copy of Lars timing paper from www.corvettefaq.com if you're not familiar with the technique we commonly use around here.
If that sounds, correct, check your timing (it can't hurt). And while you're in there, check your mechanical and vacuum advance systems for proper functioning. Download a copy of Lars timing paper from www.corvettefaq.com if you're not familiar with the technique we commonly use around here.
Ok, Problem solved. It was the timing. Its way off base. Thats for the help guy's !