At wot, losing 1000 rpms for 5 to 10 seconds.

[Steve BK]

I just got the boat, and it has two 2003 yamaha f115's. Sometimes when I try to get on plane, it feels like the transmission in a car slipping, other times its great. Also at wot (or close to it) I was at 5000 rpms, and it would suddenly drop to 4000 on one engine, then 5 seconds later go back to 5000. At idle, they both sound great, no stumbling, or missing. I marked the props, and they have not spun.

 

[Scott Danforth]

either fuel system or your ventilating the props

 

[Steve BK]

When it drops down in rpms, it still feels smooth, just lower rpms. I doubt its prop ventilation due to smoother gulf water, and I had the engines trimmed all the way down to take off. Once on plane, I lifted both the same, and only one does this.

 

[Steve BK]

I will add that the guy I got it from said he put seafoam in the gas with this tank, and it is only down to 3/4. Could seafoam cause that?