Rough cold idle '81
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Joined: Nov 2005
Posts: 88
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From: Azusa California
Rough cold idle '81
My stock engine runs a bit rough when cold - smooths out as it warms up.
When I start it, the idle is only 500; so it would seem the choke is not working correctly.
Comments/suggestions/experience welcome....
Thanks
When I start it, the idle is only 500; so it would seem the choke is not working correctly.
Comments/suggestions/experience welcome....
Thanks
Melting Slicks
Joined: Aug 2004
Posts: 2,924
Likes: 229
From: Oakbank Manitoba
Sounds like the vacuum break diaphragm is ruptured. This is the small cannister in front of the choke. If the diaphragm (rubber) inside the cannister is ruptured the choke will not unload slightly at idle. When the engine is first started (cold), the choke wants to close completely. The vacuum break diaphragm pulls the choke valve to a preset opening once the engine is started. This opening is usually about 1/8 to 1/4 inch. If the diaphragm is ruptured ....no opening will take place. The engine will run rough and want to stall because it isn't getting the required amount of air needed. Once the engine starts to warm up and the choke starts to open....the idle will stabilize. Easiest way to tell if it is working is to start the car when cold...observe the opening (slightly) of the choke valve. If there is no opening of the choke valve 1/8 to1/4 inch and the choke valve remains completely closed then the rubber diaphragm is ruptured. You can test it by removing the vacuum hose to it .....push the arm into it then cover (with your finger) the vacuum port. The diapragm should hold it in. If it pushes back out while your finger is covering the port then you have found the problem.They are easy to change and not very expensive.
