carb needle adjustment

[jonathan]

I read that the needle valve adjustment should be at about one to two turns open when running. The needle adjustment on my car only opens just over a half turn from closed! Carb was rebuild a couple years ago. Runs great pulling hills but idles a little rough. Is there a way to make it open more? Thank you

[Dan Hatch]

There is no magic number of turns for a carb. Just a starting point for your to find where it runs the best.

[Norman Kling]

Idling rough can be caused by several things. Low compression in one or more cylinders. Dirty timer or coils out of adjustment. If you are running on magneto, try different positions of the spark lever to see if the idle smooths out. If the coils are not perfectly adjusted, one could spark earlier than another. It could also be too wide a gap in one spark plug. At idle, the spark should be more retarded than when running at higher speed.
The carburetor float setting could be high causing more gas to be drawn into the cylinder at idle. Or more likely, at sometime, the idle needle has been turned down too hard causing the tapered end of the needle to wear a groove. Having said all the above, If it runs as good as you say it does, just leave it alone. Set the idle just a bit higher so you don't kill the engine when idling and don't worry about it until you do a major tune up sometime in the future.
Norm

[CudaMan]

Are you saying that the car dies with more than 1/2 turn open, or the needle is physically stopped from turning more than 1/2 turn open? If it's the latter, there is a slotted packing nut that the needle passes through. Try loosening the nut to allow for easier/more turning of the needle. Don't go too loose or the needle will start turning by itself.

If you want to inspect the needle, loosen the packing nut all the way and unscrew the needle from the carburetor. If the tapered end has a groove worn in it from being tightened too tight, you can dress away the groove like this:

https://www.youtube.com/watch?v=uTiStUTU9IE

[Adam]

Starting point for a properly rebuilt Holley NH is generally 7/8 turn open (that is “seven eighths”, which is just less than 1 turn). At this point, it will generally start and run, but your particular “good running” adjustment could be anywhere from 1/2 turn to 1+1/2 turns open. This depends on your fuel, altitude, variation in the spray needle and nozzle, etc. Any more or less and something is wrong that may require repair.

Unfortunately, many “rebuilt” carburetors are just that... Someone took it apart, cleaned & painted it, and put it back together.

[jonathan]

Thanks everyone!