Curious carburetors

[rsessoms]

My 48 Cub that I've basically gone through from front to back has a curious quirk I can't figure out. It is a hard starter now because of the fuel system. It's almost like I have to heavy a gas flow when starting. I don't open the sediment bowl until it starts up, yet gas still leaks out the bottom of the carb.
I had the original one professionally rebuilt and it is the worse acting one and it will only run with the choke pulled out and still drips. The float is fine, set right and not sticking.
I have an import that I have switched over to and it works fine, yet still drips until it is running well and sediment bowl opened up.
The tank is clean and I have cleaned all screens and blown air through the lines.
The only thing I haven't done is to change the line over from rubber to steel. It came with a rubber line that was old and put a new one on.
None of my other Cubs have the drip.
Any ideas?

[Eugene]

Faulty needle valve and seat, wrong float setting, float rubbing on inside of bowl.

My first guess, needle valve and seat is the priority thought. Do a bench test for needle valve leaking and float height setting.

[Don McCombs]

Assuming all the checks you have stated above, consider that you may have a manifold gasket leak that allows excess air to enter the fuel mixture prior to ignition, creating a lean condition. To check for this, start the engine and keep it running with the choke. Open the fuel valve on a propane torch, but do not light it. Aim the torch at the manifold gasket area and run it around the perimeter of the gasket. If, at any time, you get an increase in RPM, you have a inflow leak. This could becaused by a broken gasket, cracked or rusted through manifold or a loose manifold.

[Rick Spivey]

Keep in mind that with an updraft carburetor, it is fairly normal to have some fuel leak out the weep valve on the bottom of the carb, especially when using the choke to help start. I have three running cubs and each one requires a slightly different amount of choke to start, ranging from none to "one pull with choke one, then take choke off for subsequent pulls" using a hand starter.
You also indicate that you are starting on residual fuel, then opening the gas valve after start. I don't see that this should contribute to hard starting, as there is usually a couple minutes of run time at idle in a fuel bowl. I know this because I practice the opposite practice, I run all the fuel out when finished with the cub, even just for one day, and then open the fuel valve up to start the next day. My use can range from daily to very sporadic, and I don't want today's gas in the fuel bowl for any length of time.

[rsessoms]

Excellent idea about using propane torch to test for leak!
I typically run the gas dry on all of my machines too, but have learned not to with this one.
My carb guy tests every one he does before sending out. The other one he did works like a dream.
I'll try to check the manifold leak this afternoon.