My first thought is that your accelerator pump must not be giving you a full shot, but then you say you have to hold down the gas pedal, which holds open the choke plate to provide more air, usually in a flooded situation. Those sound counter productive to me, pumping the pedal to get fuel, then holding the pedal down to get more air. If you have good spark, timing's right, etc then I would expect one pump to prime and set the choke, then crank and start. Your explanation is confusing to me - does not seem logical.