If a carb engine stumbles when you accelerate hard but runs ok if press it easy. would that indicate too lean or too rich? SC
Could be either one . . . or it could be something to do with the timing (bad vacuum or centrifical advance in the distributor) . . . but most likely it's leaning out on accelleration due to a non-functioning accelerator pump. A carborator works kind'a like a toilet . . . stuff (gas in the case of the carb, ummm "stuff" in the case of the toilet) just sits in the bowl until something sucks it out. Air rushing in through the carborator sucks gas out of the bowl as it goes through. Water rushing out of the tank heading down the drain sucks whatever is in the bowl down with it (at least we hope it does).
If you are going half throttle for a while, the constant rate of air flow pulls out a constant rate of fuel to mix with it. Rich/Lean is determined by the size of the jet(s). Let's say you have the perfect jetting in the carb and you have the perfect air/fuel mixture while you're running half throttle . . . all at once you stomp the gas pedal and the throttle opens all the way. The air flow through the carborator will increase dramaitcally and almost instantly . . . but it takes a second for the suction on the fuel to increase and get it back to the perfect mixture. During that time you have way too much air and not enough fuel so the engine boggs down. That's where the accelarator pump comes in. It's job is to squirt extra fuel into the throat of the carb while the throttle is opening to give time for the fuel being sucked out of the bowl time to catch up.
Now if you're running a "009" dizzy and a "34" carb, you're engine is going to stumble on accelertion no matter what. In that case, talk to ASBug . . . he's been there, done that. :wink:
