surging - resolved
Thread Starter
Le Mans Master
Joined: Oct 2006
Posts: 8,940
Likes: 35
From: El Cajon California
surging - resolved
My 1978 Corvette has been plagued by surging issues while driving, anything more than gentle acceleration caused bad surging. Background, car was running real bad, bushings in distributor were shot, causing rotor contact with the cap. I bought a msd street fire car ran much better, but surged. I timing from 6 to 12 degrees all surged, played with springs, plugged minor vacuum leaks but the car still surged.
I plugged the vacuum advance and the surge went away.
I was curios why?
I plugged the vacuum advance and the surge went away.
I was curios why?
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,117
From: Crossville TN
My guess....
The rubber diaphragm in the vacuum advance canister is torn/split just a bit. It sealed well enough to move the diaphragm under good vacuum, but with more tension in the diaphragm the split leaked more. So, it just went from trying to pull in more timing, then leaked off to get less. Back and forth--
Pull the hose off at the carb and suck on it. You will likely be able to get some air through it. If you do, just buy a replacement vacuum can for the distributor and change it out.
The rubber diaphragm in the vacuum advance canister is torn/split just a bit. It sealed well enough to move the diaphragm under good vacuum, but with more tension in the diaphragm the split leaked more. So, it just went from trying to pull in more timing, then leaked off to get less. Back and forth--
Pull the hose off at the carb and suck on it. You will likely be able to get some air through it. If you do, just buy a replacement vacuum can for the distributor and change it out.
Race Director
Joined: Jan 2000
Posts: 12,399
Likes: 247
From: San Jose CA
The rubber diaphragm in the vacuum advance canister is torn/split just a bit. It sealed well enough to move the diaphragm under good vacuum, but with more tension in the diaphragm the split leaked more. So, it just went from trying to pull in more timing, then leaked off to get less. Back and forth--
However, I'm also inclined to believe that the balancer may have slipped and the 6-12 degrees is more advanced than he might think.
