Re: dead spot in accelerator
By your last description I would definately lean towards what Tommays says. The accelerator pump in the carb probably needs attention. When the engine is cold you have a closed choke running a rich fuel mixture. <br />You probably have a basic understanding of carb operation. If not, when you open the throttle, it opens a flapper at the base of the carb. This lets the downward stroke of the piston suck air into the cylinder through the carb throttle body. This air flow creates a low pressure which draws fuel into the air stream at a metered rate. This is why the throttle body or air horn of the carb is slightly hour glass shaped, it is called a venturi and is similar to an airplane wing in theory. The fuel flow is drawn into the air stream and drawn into the cylinder. <br />When you go from idle to open throttle, there is a rush of air being drawn into the cylinder, but it takes a brief instant before the fuel gets caught up in the air stream. This is when the stumble occurs. Sometimes it results in a backfire through the carb, most of the time it is just a dead spot for an instant. The accelerator pump is just what it is called. It forces a small mist of fuel to squirt into the air stream at the instant your throttle opens. This maintains a proper fuel air ratio entering the cylinder. On a colder engine, even on a warm day, the choke will either be closed or be partially closed with the choke spring relaxed. The air rush coming in is slightly restricted by the choke being pulled shut. This allows the air draw to pull more fuel than when the choke is full open on a warm engine. So, do as Tommays says, on a cold engine with engine OFF work the throttle open and look for an un-interupted squirt of fuel into the carb. It should squirt the same amount through the entire throttle opening. If it doesn't, either a bad power valve, accelerator pump or out of adjustment or dirt somewhere in the carb. Possibly try some gummout or sea foam injector cleaner in the gas tank. The gummout spray is designed for linkages and surface cleaning only. <br />of course it could always be elictrical!<br />Good luck and let us know!
