i have an arien snowblower 5 hp model number 932006. It has an eletric start an no primer. i pull out the choke when starting it (it has o, 1/2, 3/4 and full setting). once the snowblower is started, i push the choke in and it stalls out. the snowblower will run for periods of 10 to 15 minutes when i play with the choke a bit but it is still out at around 3/4. Any ideas on why this is happening?