Did you get the accelerator pump together wrong or plug up one of the passages by accident? Check to make sure it gets a healthy squirt of gas by pumping the accelerator with the engine off while watching down the bore. Also, make sure the power valve is working. It senses a drop in vacuum and richens the mixture for acceleration. If you got the wrong spring on it, it's vacuum passages are plugged (by goop or a misplaced gasket) or it is stuck it will do exactly what you described.


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