Last run of the year last summer and I started having trouble w starboard engine. Starts fine. Idles fine. Run both engines upto 2800 rpm and goes on plane. Go up to 300 rpms and motor stutters for a second and drops to 2500 rpms. comes back up to 3000 then drops to 2500. If I throttle more and go to 3500 the lag gets worse and still drops to about 2500 and takes longer to hit again and get back upto 3500. If I go w more throttle I could get it to stahl. When I run it on the hose I can tell anything is wrong. I replaced the cap and rotor and coil becasue they were 8 years old and did the other motor earlier in the year because the coil died. Checked fuel filter and it was totally clean. Swapped fuel pumps. I did those things but was never able to get on the water again to see if anything happened. Its mid winter and thought I would see what the wonderful world of OSO would have to say. Btw It ran fine the day before. All gauges reading normal

Sure sounds like fuel starvation to me Pete.... were you able t monitor fuel pressure?? Are you carbed or efi ?

ya like phragle said we need more info on the engines, sounds like a fuel issue or timing not advancing

I had 2 similar issues.
1. My secondaries got contamination in them and boat would run great until the secondaries were opened.
2. Ground wire loose/broke (inside shrouding) on my ignition box.

They are carbed 600 cu in. MSD ignition. Fuel pressure stays steady.

How old are the plugs ? might want to swap ignition boxes and see if the problem follows.

Plugs are 7 years old. Irridium plugs. My next 2 thoughts are to swap boxes and carbs (one thing at a time of course) but I wanted to see if there is something I haven't thought of yet.

I'm thinking the carb is flooding, needs cleaning

Im gald you said that. I did look at the float/fuel level through the sight glass. It was normal when not running. But does that mean anything? Also, would it most likely be the secondary float or primary?