Hello Folks, I have a couple of carbs that I would like to "leak-check" the needle and seats. I have an idea that might work. I will be doing this with the fuel bowl removed, so I can manually move the float up/down to shut off the gas. My first thought would be to use compressed air at low pressure thru the carb fuel inlet, but I don't know if that may damage the rubber needle tip. In order to see it leak air, The carb would be underwater in a bucket, watching for bubbles.
Hopefully you guys have some ideas how I can make good with a leak check. Thanks, Nitro.

Stay away from the compressed air. We simply bench test em by filling the float bowl, let em sit and see if fuel leaks out.

yes stay away from compressed air, what I do, is I tip the carb upside down so that the float has the needle down, and blow into the inlet and listen, if you air leaking out with very slight pressure, than you should replace the needle & seat, if not, you should be ok

yes stay away from compressed air, what I do, is I tip the carb upside down so that the float has the needle down, and blow into the inlet and listen, if you air leaking out with very slight pressure, than you should replace the needle & seat, if not, you should be ok

Pyro, Were talking air here, which will show a leak before a liquid would leak. Also, With small pressure it will overcome the weight of the float then leak. I agee with your check, but it seems to me that we are talking very little pressure to lift the float. Would this really be the same "little force" that gas filling the bowl would exert pressure wise ? I believe the pressure of the gas on the float would exert a slighter greater force on the needle to seal the seat, Because a liquid is not compressable.
Hey ... Everybody, or anybody Please Jump in here, and give me Your take on this. Thanks-To-All, Nitro.

Oh heck, you can use compressed air to check carburetors for leaks, but you need to limit the output to 10 psi or less. If it will hold at least 4 - 5 psi you should be alright. I have a small hand pump with a gauge that I use to check them with.

Oh heck, you can use compressed air to check carburetors for leaks, but you need to limit the output to 10 psi or less. If it will hold at least 4 - 5 psi you should be alright. I have a small hand pump with a gauge that I use to check them with.

Hey 30, Your a day late .... Great technique, I used my small portable 12v air compressor. I just used a neopreme line to connect the two, then flipped the switch on, and off, and watched the initial 40 psi drop fast to 30, a little slower to 20, and then at 10 it stayed for a minute. Finally, went to 4, or 5 psi, and held for at least 3 mins.to a max. of 5 mins. Does this procedure represent a true leak check of the needle, and seat ... when you figure in the weight of the float pushing down on the needle / compared with the actual ... the float being pushed up from gas in the fuel bowl to seal the needle, and seat ? Which would make a tighter seal ??
What say you of that .... Good, or OK. ? Thanks, Nitro.

I think you will get a slightly tighter seal with fuel in the float bowl vs the weight of the float. If it's holding 4 - 5 lbs. you should be good to go.