I just put a new Holley Truck Avenger carb on my 390 and I think I might have some jetting problems. The truck starts and idles fine but there is a bad off idle stumble, if you floor it right off idle the truck dies. I have no experience with jetting and adjusting carbs so not sure what I should try first. I live at 6000ft and the box said the carb was jetted for sea level so that was my best guess. Anyone have an idea to point my in the right direction? Thanks for the help, jake.

 

It's a new carb, but just to make sure, take the aircleaner off, and with the engine off, and while looking down the carb throat, push the throttle back with your hand. You should see two strong streams of gas flowing down the carb throat. If you have a double pumper, you should see 4 streams, front and rear.

If that is working, then I would set the secondaries tighter if this is a vacuum secondary carb. They may be flying open to quickly, making the engine lean out too much.

If you have a double pumper carb, you may never get rid of it. If you have a single plane intake, I am pretty sure you will never get rid of it, especially if this is a full size truck with over size tires and stock gears.

 

You may need to change squirter size and/or adjust the pump lever. This is after you verify the pump is squirting into the carb.
Also, make sure that the timing is correct and that the vacuum advance is hooked to the metering block port and is functioning.

 

Did you ever get this fixed?