1987 Evinrude 175hp cuts out

[knarfztnark]

My 1987 Evinrude 175 started acting up this past weekend. It has a low speed miss and when I start to accelerate the motor will cut out and go to half power momentarily. Without touching the throttle it will then cut back in to full power and might run at top speed for a few mins until it cuts back out again. Someone told me that it might be an air leak in the fuel system causing the problem but I am tending toward an ignition system problem as a more likely cause. Any advise will be appreciated. thank