Distributor
Thread Starter
7th Gear
Joined: May 2019
Posts: 7
Likes: 1
Distributor
1975 C3 corvette with a 350. I just replaced a defective ignition module The timing fluctuates at idle. When I reattach the vacuum hose, the engine dies. Do I have bad springs or weights in the ignition distritutor? When I disconnect the vacuum hose from the distributor it seems the engine runs ok.
Le Mans Master
Joined: Aug 2017
Posts: 8,336
Likes: 2,810
From: Cool Northern Michigan
If you mean the timing mark fluctuates at idle, that's par for the course with some timing lights. They have difficulty receiving a good signal from the plug wire then relaying that impulse through the light. The light beam will jump between two known marks.. You have to figure out which is correct. Usually the lesser mark..
I doubt the actual timing is moving but maybe. If the engine dies with Vac, you must be too advanced. Plug the Vac off, loosen the dizzy and set your total around 34-36 at a high RPM, above 3K. Once that is set and locked down, then reattach the Vac. By the way, the Vac line moves the plate under the weights & springs. Two different systems: Mechanical Adv and Vac Adv.
On the springs & weights? Hard to say unless the timing TRUELY is all over the place. But for now get your Total Timing (w/o vac) established.
I doubt the actual timing is moving but maybe. If the engine dies with Vac, you must be too advanced. Plug the Vac off, loosen the dizzy and set your total around 34-36 at a high RPM, above 3K. Once that is set and locked down, then reattach the Vac. By the way, the Vac line moves the plate under the weights & springs. Two different systems: Mechanical Adv and Vac Adv.
On the springs & weights? Hard to say unless the timing TRUELY is all over the place. But for now get your Total Timing (w/o vac) established.
Tech Contributor
Joined: Jun 2004
Posts: 20,934
Likes: 962
From: I tend to be leery of any guy who doesn't own a chainsaw or a handgun.
1975 C3 corvette with a 350. I just replaced a defective ignition module The timing fluctuates at idle. When I reattach the vacuum hose, the engine dies. Do I have bad springs or weights in the ignition distritutor? When I disconnect the vacuum hose from the distributor it seems the engine runs ok.
Thread Starter
7th Gear
Joined: May 2019
Posts: 7
Likes: 1
If you mean the timing mark fluctuates at idle, that's par for the course with some timing lights. They have difficulty receiving a good signal from the plug wire then relaying that impulse through the light. The light beam will jump between two known marks.. You have to figure out which is correct. Usually the lesser mark..
I doubt the actual timing is moving but maybe. If the engine dies with Vac, you must be too advanced. Plug the Vac off, loosen the dizzy and set your total around 34-36 at a high RPM, above 3K. Once that is set and locked down, then reattach the Vac. By the way, the Vac line moves the plate under the weights & springs. Two different systems: Mechanical Adv and Vac Adv.
On the springs & weights? Hard to say unless the timing TRUELY is all over the place. But for now get your Total Timing (w/o vac) established.
I doubt the actual timing is moving but maybe. If the engine dies with Vac, you must be too advanced. Plug the Vac off, loosen the dizzy and set your total around 34-36 at a high RPM, above 3K. Once that is set and locked down, then reattach the Vac. By the way, the Vac line moves the plate under the weights & springs. Two different systems: Mechanical Adv and Vac Adv.
On the springs & weights? Hard to say unless the timing TRUELY is all over the place. But for now get your Total Timing (w/o vac) established.
Le Mans Master
Joined: Aug 2017
Posts: 8,336
Likes: 2,810
From: Cool Northern Michigan
That reminds me of something else. Remove the coil dust cover, three phillip screws. On one corner of the "coil in cap" is a GRD wire under one of the four mounting screws. Sometimes the coils are painted so well that a good Grd is impossible. Remove that Grd wire and screw. Take a small wire brush and remove the coating on the coil where the GRD wire goes. Put it all back together.
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Le Mans Master
Joined: Sep 2001
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From: Unreconstructed, South Carolina
Just an FYI item to check. On old vehicles with an HEI distributor, it's not uncommon for one of the two wires connecting the pickup coil to the ignition module to fatigue/break due to the wires flexing every time the vacuum advance canister rotates the "breaker" plate. Perhaps a resistance/continuity check of the pickup coil while moving the "breaker" plate might be an item to consider checking.
replace distributor pickup assembly ... Standard Ignition pn LX-302 ... or ... LX-302T
Thread Starter
7th Gear
Joined: May 2019
Posts: 7
Likes: 1
I cranked the engine over until I got the line on the harmonic balancer to TDC. I then removed the distributor cap to check to see if the rotor was pointing to the number one plug wire. It was pointing 180 degrees off. It looked like I have the rotor on backwards. What am I doing wrong?
Thread Starter
7th Gear
Joined: May 2019
Posts: 7
Likes: 1
I cranked the engine over until I got the line on the harmonic balancer to TDC. I then removed the distributor cap to check to see if the rotor was pointing to the number one plug wire. It was pointing 180 degrees off. It looked like I have the rotor on backwards. What am I doing wrong?
Burning Brakes
Joined: May 2013
Posts: 789
Likes: 129
From: Los Banos CA
I cranked the engine over until I got the line on the harmonic balancer to TDC. I then removed the distributor cap to check to see if the rotor was pointing to the number one plug wire. It was pointing 180 degrees off. It looked like I have the rotor on backwards. What am I doing wrong?
