Carter Yf And Idle Problem

Applying starter fluid, or raw propane, near a suspected vacuum leak can indicate by altering the engine idle.

No gasoline should be leaking IMHO.

"I’ve had my carb “rebuilt,”" That can mean vastly different things to different people. YF's were used on many vehicles, but need certain unique parts for a Jeep application, for instance the float valve and needle, that some kits do not provide, and which are set to different specifications.

 

"Hunting", also known as surging, Can be from an improper float setting. There are currently a number of different needle and seat designs available and each requires a different float setting. It could also be a low-speed jet that is too narrow in diameter, and/or an improper metering rod setting. There should be zero slop in the throttle shaft. If the carburetor hasn't been attended to in decades it is likely that the shaft and the bores in the throttle are worn into an egg shape. A gap as small as .005" is a vacuum leak. This means more air is allowed in which leads to a lean mixture only addressable by increasing the fuel flow via the mixture screw and running with the choke applied. Eventually, this leads to a very high idle. Once the problem has progressed to this point, leak testing will reveal nothing.