1999 SeaRay 270 with 7.4L MPI & BravoIII Power Loss

[Bigdog98]

Hello all. I am new to this thread and looking for some advice. I purchased my 270 Sundancer in January of this year and had it surveyed. Report came clean and at the day of the survey there were 5 people on board with a half tank of gas. With this weight , the recorded speeds where at 4600 RPM which was WOT it reached 35-36MPH. At the time of this report the bimini was stowed away and the bottom paint was in really poor condition. I had added barrier coats to the bottom and anti fouling paint as I was suggested since my boat sits in a slip for 5-6 months in slat water. Now I find that with 2 people on board and a quarter tank of gas my boat tops out at 31-32 mph and around 4200 -4400 rpm. I checked the props and they look good. I did hit a sand bar maybe 2-3 times this season. Bottom paint looks clean and was cleaned under water every month during the summer season. The props are 22p duel prop on what I believe is a 2.00 bravo 3. I did read up on this same exact situation but had a hard tie understand what people were saying. I also did a compression test less than a month ago and all 8 cylinders came out at 160-155-165 psi. Anyone have any suggestions? Thank You

 

[Lazy Daze]

It sounds like the engine was performing well within specs at the time of the survey. So unless you have changed something or added a ton of extra weight, I wouldn't be looking at a prop change or anything like that to solve the issue. Normally, I would next look at the bottom paint and possible slime growth on it as that is a very common thing to cause what you're seeing. If you're positive that the bottom paint is clean, then I would next look at fuel quality issues/plugged filter or plugs/wires/cap/rotor, etc.

But, if it's been some time since the bottom has been cleaned (and it hasn't been run much lately), I'd take a dip with a mask and look at/feel the bottom for slime.

 

[Bigdog98]

It sounds like the engine was performing well within specs at the time of the survey. So unless you have changed something or added a ton of extra weight, I wouldn't be looking at a prop change or anything like that to solve the issue. Normally, I would next look at the bottom paint and possible slime growth on it as that is a very common thing to cause what you're seeing. If you're positive that the bottom paint is clean, then I would next look at fuel quality issues/plugged filter or plugs/wires/cap/rotor, etc.

But, if it's been some time since the bottom has been cleaned (and it hasn't been run much lately), I'd take a dip with a mask and look at/feel the bottom for slime.

Ill be honest , I have not changed the plugs , cap & rotor or wires so these things are 2 season old. The plugs are nasty and black but that's understandable for 2 seasons. The only thing i did was change water separator filter and oil filter and oil. But can that really cause that big of a decrease of speed? The water is in the low 60's right now so hard to take a dip bit it looks clean. Ill take a gopro under there. I run the boat 2-4 times a week. Added 150 hours in one season.

 

[scoflaw]

Spark plugs in an MPI engine should never be nasty black no matter how old they are, and 2 years isn't old. That alone could be your problem, I'd be looking in that direction, like in FULL tune up. Make sure they are the correct plugs

 

[Bigdog98]

Spark plugs in an MPI engine should never be nasty black no matter how old they are, and 2 years isn't old. That alone could be your problem, I'd be looking in that direction, like in FULL tune up. Make sure they are the correct plugs

I only assume they are 2 season old. I purchased the boat with no service record. Ill post a pic of the plugs.One change that I did do is switch to synthetic oil but I believe it is not good for my engine as my engine has near 530 hours on it and the seals are probably worn out already. I find myself adding some oil time to time. Maybe I will switch back to conventional oil next season but some people say its a bad idea.

 

[Bigdog98]

 

[Bigdog98]

I was talking to a guy today who has the same boat and he has the back prop a 4 blade and front a 3 blade. Anyone hear of this being a thing? He says he gets 28mph at 3100 rpm and planes at 2600 rpm.

 

[BillK2632]

Plugs lake look fine at least from the pictures. But change them anyhow since you don't know the history. So exactly
how hard did you "touch" the sandbar? Any vibration?

 

[Bigdog98]

I touch them at about 2000 rpm and as soon as i felt it i immediately raised the drive up. The propslooks good to me. Maybe a small nick on the edge but no major chunks missing or bent looking.

 

[BillK2632]

Then props are probably ok, if you bent something there would be a vibration. I'm not a saltwater boater, but I think I would go back to growth being the issue.