Losing RPM

[harl14]

I just purchased a used Carolina Skiff with Suzuki DF90 (both are 2007).The gas smelled sour.I cleaned the gas tank,replaced fuel hoses and water seperator.Upon running down the lake for about a mile at 4,000 RPM it would fall back to 2,000.You could run at this speed for about 5 minutes and it would repeatedly do this again and again.What could be wrong?

[Garbo50]

My 2009 DF90 does the same thing ? I don't know what it is.

[boats.net]

May need to remove and clean VST.

[Garbo50]

RMP Problem

Well.....after cleaning the tank, filter, separator, and running some marine stable through the motor, no luck. Then I changed all 4 sparkplugs....problem fixed. Runs smooth, steady rpm. Spark plug problem the whole time !