I recently purchased a 1989 232 Gulfstream Grady White with twin 1993 Johnson Ocean Runners 175 J175EXETR and J175NXETR. Went thru both motors, even compression on both, verified all warning alarms working, still running OMS. Replaced all thermostats, plugs, water pumps and lower unit oil. I have had the boat out a couple of times and both motors crank right up and appear to run well. Boat jumps out of the hull very well and will cruise right at 30 mph @4000 rpm (15 1/2 X 17 3 blade SS Solas). I did the 3/4 gallon of gas to 16 oz seafoam treatment to both motors on the second trip out. I did not notice much difference between the before and after.

During some point of running (idle) at home on the hose I noticed the port bottom carb on the stbd motor had a little blow back coming out of the carb throat. Not a backfire but a consistent slight "flow". It is not much but definitely there. The question is; can there be anything other than a reed valve that would cause this? I have had the boat out a couple of times and both motors run very well and idle without stalling out.

Like I said that boat is new to me so I don't know the maintenance history. From the research I have read online reed valve damage/failures are rare and I don't see any of the common symptoms (ie rough idle, hard starting). Thanks for the input.