Originally Posted by
bmorgil
thumper, I am going to say the idle circuit on that new carburetor is clogged. It can happen from sitting on the shelf. It is a touchy little thing. I have a few posts about that circuit. The classic symptom is "wont idle without some choke". Unfortunately the fix is to pull the carb back down and run a fine wire through the idle jet. I have head a few say it suddenly started idling OK. Sometimes it will clean itself out. Usually it clogs until you clear it with a wire. All you need is a little piece of dirt in the fuel from working on the open lines etc and it will clog. A good inline fuel filter is imperative with these carbs.
The fuel is supplied through the idle circuit until the throttle blade is open about 10 degrees or so. At that point the transition and main fuel circuits pick up the fuel supply. When the choke is on it pulls fuel through the main and transition circuit. If the idle circuit is clogged there will be no fuel at idle and slightly above. With the choke on fuel is being pulled in through the main circuit and the engine will idle.