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Hello, Where would be a good place to start tracking down a vacuum leak on these 78 1000s? I know i have one (which i believe is causing my strange idle issue) but i cant really seem to get consistent results when i spray around the carbs with carb cleaner. Im thinking its coming from around the number 4 carb. When i got home from work today before i shut it off i sprayed around the number 4 carb and the idle did change, not a lot but definitely noticeable. Its driving me crazy!
 

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There are only 2 places it couls have a vacuum leak, either where the carb joins the intake or where the intake joins the head.
 

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At the base of the rubber lines is an air jet. So the rubber line could leak, but the jet would meter air in just the same. The other end on the plenum is connected to your air cutoff valve. Might affect deceleration farts.

Try an unlit propane torch. You should be able to pinpoint the leak. If it’s the rubber atop the elbows, trying tightening them with a warm/hot motor. The orings under the elbows can get torn easily.
 

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Couldn't be from one of the rubber lines? Or the top of the carbs where the caps bolt on?

At idle, manifold vacuum is contained between the closed throttle plate and intake valve. As throttle opens a venturi vacuum is created in the carb throat acting upon main and secondary main (if equipped) circuits drawing additional metered fuel into the intake air stream . If the rubber hose were attached to the no. 4 intake runner or a ported vacuum connection of carb it could, simply pinch off the suspected hose with pliers and that will tell you if it is leaking vacuum with an RPM change if lean due to a vacuum leak.
 

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Hello, Where would be a good place to start tracking down a vacuum leak on these 78 1000s? I know i have one (which i believe is causing my strange idle issue) but i cant really seem to get consistent results when i spray around the carbs with carb cleaner. Im thinking its coming from around the number 4 carb. When i got home from work today before i shut it off i sprayed around the number 4 carb and the idle did change, not a lot but definitely noticeable. Its driving me crazy!
Some of the carb cleaners will not have an affect when sprayed around the vacuum leak. They are just not volatile enough. Ether, propane or mass airflow cleaner will work much better.
 

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I've had a lot of luck with an unlit propane torch in the past. I third that method.
 
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