I have 1975 evenrude stinger gas been parked for two years,but before parking the carbs were boild out. the motor runs great on top end but will not idle. I have checked the spark plugs,and gas filter and tried to adjust the idle but it still will not idle.could this be the low speed jets? if so how can I fix them,and how do I adjust the carbs it has no external adjustments and I have used new gas