Vacuum advance question
Thread Starter
Cruising
Joined: Mar 2001
Posts: 11
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Vacuum advance question
Here is a tough one, for me atleast.
When I start my car cold it idles fine with the vacuum advance line hooked up. Once it is warm it idles about the same with or without it hooked up. Here is the wierd part Anytime I open the throttle with the vacuum advance hooked up the motor revs for 1/2 a second then dies then revs for 1/2 a second then dies. And when I take the advance off it revs fine. Any ideas? Also would it be safe to drive the car like this??
When I start my car cold it idles fine with the vacuum advance line hooked up. Once it is warm it idles about the same with or without it hooked up. Here is the wierd part Anytime I open the throttle with the vacuum advance hooked up the motor revs for 1/2 a second then dies then revs for 1/2 a second then dies. And when I take the advance off it revs fine. Any ideas? Also would it be safe to drive the car like this??
Racer
Joined: May 2000
Posts: 386
Likes: 0
From: Niedernhausen, Germany
Re: Vacuum advance question (70LT1)
I would shoot for a blown vacuum (leak) actuator in your distributor. When it's warmed up and you disconnect the vacuum, hardly anything changes just because that leaky actuator did not pull any advance at all.
To check, remove distributor-cap, pull the vacuum hose from the carb and suck on the end with your mouth. The vacuum actuator should react easily. If he does not and you hear a whistling sound, the actuator is done.
The weird symptom is explained like this: The leaky actuator acts like an ordinary vacuum leak, i.e. your idle vacuum is lower as it should be - with no leak, more vacuum would be present and more fuel would be come in from the idle bleeds. But your idle-screws are adjusted in order to give enough fuel with the lower vacuum at idle. However if you open the throttle, vacuum drops further down and for this moment, the fuel is not sufficient any more. So the engine dies.
To check, remove distributor-cap, pull the vacuum hose from the carb and suck on the end with your mouth. The vacuum actuator should react easily. If he does not and you hear a whistling sound, the actuator is done.
The weird symptom is explained like this: The leaky actuator acts like an ordinary vacuum leak, i.e. your idle vacuum is lower as it should be - with no leak, more vacuum would be present and more fuel would be come in from the idle bleeds. But your idle-screws are adjusted in order to give enough fuel with the lower vacuum at idle. However if you open the throttle, vacuum drops further down and for this moment, the fuel is not sufficient any more. So the engine dies.
