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Weber carb idling high


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So I haven't changed anything on the carb yet but it started idling at a high rpm. Without taking the carb off or apart it appears everything is still operating properly, the choke is open all the time though.


The idle speed screw is not touching the lever, and I tried turning in the idle mixture screw (less fuel?) And it continues to idle high. Is there anything else I should check before pulling things apart?


Not sure if it matters but a cap that was on the valve cover PCV connection feel apart right around the time I noticed, but putting my finger over it doesn't seem to change anything.

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High idle means more gas and air is getting in. Assuming your idle mixture is correct then a vacuum leak would add more air and the idle would be worse. Too much air not enough gas. Look to see if the throttle plate on the primary is properly closed. Throttle shaft wear may allow the plate to become cocked in the bore. A sudden stab of the gas often releases it. Is the choke mechanism (fast idle?) holding the throttle open? Throttle cable too tight? Now look at the secondary throttle plate. Is it fully closed??? It is interlocked to the primary but should be shut tight at idle and up to around 1/2 throttle. 

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The throttle cable is pretty loss and the lever is completely forward so I don't think the throttle is engaged. I looked into the opening at the throttle plate and the primary is titled a little at neutral setting and the secondary looks slightly open but it's pretty hard to tell for sure. The idle lever adjustment is completely off the linkage. Is there somewhere else to adjust the primary and secondary throttle plates? When they are closed should they be completely level/horizontal?

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As stated if your mixture is correct then adding more air through a leak will make the idle worse. If the choke is on then yes it will rev up.



20200817-105943.jpg which is the primary and the secondary?????

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1 hour ago, datzenmike said:

As stated if your mixture is correct then adding more air through a leak will make the idle worse. If the choke is on then yes it will rev up.


 which is the primary and the secondary?????

Worse as in higher idle speed? Or slower like a tractor?


The top is the primary, it's a little wet looking because it was sitting for a bit and I had to spray some starter fluid in it to get it running again.


The choke doesn't seem to be working as it is always open as in the pictures. The carb itself is labeled as DGAV (water operated) but it has an electronic choke on it, PO must have modified it and the wire send to be connected to a 12 V source and that is it.

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1 hour ago, jagman said:

I just  had a similar problem with my weber on the 720 and found it to be a vacuum leak on the manifold. Check yours for a leak.

I'm wondering if this could be the issue. I wasn't sure how to tell if there is a leak somewhere without disassembly and replacing gaskets. I read somewhere that if you spray starter fluid around the mounting surfaces, if there is a leak it should change the idle? Not sure if I understood that correctly.

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