Starts but immediately shuts down

[Terry G.]

My 1969 350/350 with a Q-jet four barrel will start but immediately shuts down. The fact it starts, I know I have spark. Carb has fuel in it, just changed the in carb paper fuel filter.

Drove it a couple of weeks agao and it was fine.

Does anyone have any ideas?

Also as I was changing the fuel filter. the vacuum diaphram for the choke came apart. The plastic housing just split in at the seam. Is this part available separately short of replacing the entire carb and where can I get it? Checked corvette central with no luck.

Thanks
Terry Gray

[John P.]

Re: Starts but immediately shuts down

Hello Terry, There are two circuits that supply power to the ignition coil. When you crank the engine you have the starter solenoid supplying 12 volts to the coil for faster starting. When the key is released your ignition switch supplies the voltage through a resistor to the coil. Check the power to the positive side of the coil while cranking and after you release the key to the run position. If you loose power at the coil after the engine starts, you have either a faulty ignition switch, ballast resistor, wire connection at the firewall connector, or wiring. The firewall connector is a common problem.. Good luck, John

[Bob H.]

Re: Starts but immediately shuts down

Hi Terry:

John is right on the money. Put a meter on the coil and when you release the key, see if it loses voltage. If you have no voltage with the key in the on position, you can TEMPORARILY short across the resistor and see if you get it back. If not, then I would proceed to the firewall connector next. You will likely find the problem without too much trouble.

Bob

[Terry M.]

Re: Starts but immediately shuts down

My 1969 350/350 with a Q-jet four barrel will start but immediately shuts down. The fact it starts, I know I have spark. Carb has fuel in it, just changed the in carb paper fuel filter.

Drove it a couple of weeks agao and it was fine.

Does anyone have any ideas?

Also as I was changing the fuel filter. the vacuum diaphram for the choke came apart. The plastic housing just split in at the seam. Is this part available separately short of replacing the entire carb and where can I get it? Checked corvette central with no luck.

Thanks
Terry Gray

Terry,
John & Bob have the right idea -- but you have no resistor. 1968 and up has a resistance wire in the harness from the firewall connector. Regrettably there is no resistor to short out on C3s -- our loss. It is common for that resistance wire to break from the connector at the coil, but the firewall connector is also a potential problem as stated by John. Look for a off-white braid covered wire (some might call it pale yellow) at the coil. That is the end of the resistance wire. Be sure it is connected to the coil connector and terminal. If it is connected check the voltage at that wire with the ignition switch in the ON position.

[Larry M.]

Re: Starts but immediately shuts down

I had the same problem with our '72 last fall.

After much work (unnecessary, as it turned out), I found the problem to be a bad connection where the wiring harnesses meet at the firewall connector.

Larry

[Jeffrey S.]

Re: Starts but immediately shuts down

My 1969 350/350 with a Q-jet four barrel will start but immediately shuts down. The fact it starts, I know I have spark. Carb has fuel in it, just changed the in carb paper fuel filter.

Drove it a couple of weeks agao and it was fine.

Does anyone have any ideas?

Also as I was changing the fuel filter. the vacuum diaphram for the choke came apart. The plastic housing just split in at the seam. Is this part available separately short of replacing the entire carb and where can I get it? Checked corvette central with no luck.

Thanks
Terry Gray

terry,
The only plastic vacuum part associated with the choke on the Quadrajet that fits your description is the choke pull-off located on the front right of the carb. This should be available at any good auto parts store locally (NAPA, etc.) If not contact Cliff's High Performance Carburetors or Quadrajetparts.com.
Jeff