Car surging at low speed
Thread Starter
7th Gear
Joined: Jun 2006
Posts: 7
Likes: 0
Car surging at low speed
I have a 72 Vette with a small block 350 and turbo 400 Trans. At low speeds around 35 mph or so, I have a surge or possibly a miss. If I rev the motor or accelerate the car runs fine. If I am crusing at a steady speed I can still feel the surge or miss. I have changed the plugs,wires,cap, and rotor at the begining of this year, but the problem still persists. I also thought that maybe I might have a vacuum leak that might be causing the problem. Any ideas on this would be greatly appreciated. Thank you.
Melting Slicks
Joined: Sep 2002
Posts: 2,390
Likes: 2
From: New Castle DE
Timing might be to far advanced. I had the same problem with mine. The way to check is to pull in the vaccum advance line and see if it goes away. If it does then your timing is off. Here is a link to similar issue where i saw the answer wheni had the problem 
http://forums.corvetteforum.com/show....php?t=1387413
http://forums.corvetteforum.com/show....php?t=1387413
Le Mans Master
Joined: Apr 2004
Posts: 7,106
Likes: 38
From: Newark DE
sounds like the timing is too advanced.
Surging or jerking is especially pronouced when your vacuum advance to too much.
i'd disconnect the vacuum line off the vacuum can on the distributor and plug the line. See what initial timing and total timing is than drive the car. See if the surging stops.
Reconnect the vac can up again and if the surging appears again when it didn't with the vac can disconnected than you have too much vacuum advance.
If it does it with the vac can disconnected also you really have too much timing even before the vac adv but chances are if your timing is that far too advanced you will also have detonation so listen carefully for it.
Pull the vac hose off the can, plug it, check your timing levels and let us know the results plus what your motors vacuum level readings are and what vacuum can you have
Surging or jerking is especially pronouced when your vacuum advance to too much.
i'd disconnect the vacuum line off the vacuum can on the distributor and plug the line. See what initial timing and total timing is than drive the car. See if the surging stops.
Reconnect the vac can up again and if the surging appears again when it didn't with the vac can disconnected than you have too much vacuum advance.
If it does it with the vac can disconnected also you really have too much timing even before the vac adv but chances are if your timing is that far too advanced you will also have detonation so listen carefully for it.
Pull the vac hose off the can, plug it, check your timing levels and let us know the results plus what your motors vacuum level readings are and what vacuum can you have
Le Mans Master
Joined: Jul 1999
Posts: 9,206
Likes: 17
From: Sewell NJ
If you are using the stock vacuum can you are probably adding almost 20 degrees to the timing which is too much if you have worked your distributor. Read Lar's papers and get a 10 degree vacuum can and the problem will go away. It did for me.
Thread Starter
7th Gear
Joined: Jun 2006
Posts: 7
Likes: 0
Thanks guys. I will be out of town on business the next few days, but when I get back, I will let you know of the status and the vacuum readings. Thank you again for all your input, this is a great site!!!!!
Race Director
Joined: Nov 2000
Posts: 11,872
Likes: 12
From: Waterloo ontario Canada
I run into surging problems when I had the idle mixture too LEAN. I do run holley carbs and had the idle really lean but at low speeds with the engine just chugging along it surged. I richened up the idle circuit and the surge went away.
I can change the advance up to 15 degrees in the car so I tried all different advances while driving at a steady low speed but nothing helped until I riched up the idle circuit.
I can change the advance up to 15 degrees in the car so I tried all different advances while driving at a steady low speed but nothing helped until I riched up the idle circuit.
