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Discussion Starter · #1 · (Edited)
Here is the problem. Driving around... All is well. Suddenly when I stop the idle just drops to zero. Restart, drive, stop, again drops and quits. After a few times all goes back to normal. Idles, drives fine until next time. Any suggestions? Also sputter at high RPM' ... May not be related. Thanks Doug (Weber carb, 70' GT,)
 

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Über Genius
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Here is the problem. Driving around... All is well. Suddenly when I stop the idle just drops to zero. Restart, drive, stop, again drops and quits. After a few times all goes back to normal. Idles, drives fine until next time. Any suggestions? Also sputter at high RPM' ... May not be related. Thanks Doug (Weber carb, 70' GT,)
Those are the exact symptoms I had when my brake booster diaphragm started failing.

Do a quick test.
Get the engine all warmed up.
Stop the car and set the parking brake, in neutral.
Start the car.
Then depress the brake pedal.

If the car dies then there's a good chance that it's the brake booster.
 

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Über Genius
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FWIW
I also had a similar issue on GT #1 and GT #2.

It was dependent on where I bought my gas.
I was running Solex carbs on both of those so if you are running a Weber then it's probably not the gas blend.

You could have a sticky float needle valve. It would allow flooding when you idle and cause extra gas to spill into the venturi when running at speed.
 

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If you have a weber, check the idle jet on the side of the carb. Either clogged or bad O-ring. If it is that, it is a simple fix. Clear obstruction and replace O-ring.
 

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Check the vacuum hose from the intake manifold to the brake booster for any cracks or loose hose clamps, & the 1 way valve for the booster. It might not fail until the heat builds up in the engine bay. Have you done any work on the fuel system recently ? might check the small fuel filter in the front of the Weber where the fuel hose connects.

 

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Just a thought
tape a test light to the windshield
ground leg to ground
run a jumper wire to coil B+
connect to test light
take test drive
post results...does the zero rpm's align with the test light going to sleep?
 

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He is looking for you to fail by listening to him. The car will run until he lets off the accelerator, it will immediately restart and run as long as he provides throttle. Tells me either a vacuum leak or trash in the carb. The coil failing was an idea, but not under these circumstances
 

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Discussion Starter · #11 · (Edited)
So... Found vacuum leak under right side of the carb. Also changed plugs, wires, fuel filter, and vacuum hoses. Drove to Spring Hill and back from Columbia (lot of fun by the way). No problems! I will recheck with the starter fluid trick in a couple of days. Thanks for everyone's help. Doug
 

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So... Found vacuum leak under right side of the carb. Also changed plugs, wires, fuel filter, and vacuum hoses. Drove to Spring Hill and back from Columbia (lot of fun by the way). No problems! I will recheck with the starter fluid trick in a couple of days. Thanks for everyone's help. Doug

Was the vacuum leak under the heat shield? Most common spot
I would replace the 13mm carb. Nuts with nylon locking nuts.
Also found out that vac. Leak under heat shield or thick spacer gasket will never go away by just re-tighting.....re-gasket with High Tack Sealer the gaskets are soak with fuel. FWIW
Good Luck
 
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