I have a 1989 Xr4 150hp Just broke in.

However the last few time I have taken out I notice a sneeze in the exhaust. sounds like it is coughing or backfiring. only when the boat is at idle or when I am coming off plan. it only does this every now and then and it is not constant. it may only do this 3 or 4 times in an hour of cruising around. It has not affected the performace of the boat at all. it still takes off like rocket and top end is great.
thanks in advance for any info. I want to do a little sauger fishing this winter and hopefully the boat will be ready for tourney fishing this spring. dont want to blow another motor though. carbs were rebuilt 3 years ago.