Strange performance problem

C

chazaroo

New Member
Dec 4, 2006
415
Florida
Boat Info
1996 Sundancer 250
Engines
single 5.7 w Bravo III
Our 250 (5.7 Bravo III) will not go over about 3900 RPM and 29.8 is WOT. It was in for a complete service at 300 hours and now has 340. Bottom was painted in December. Anybody got an idea as to why this is the best it will do?

Chazaroo
 
Chazaroo.

Have you checked the prop for growth. I had build up on mine a few years ago.

Good Luck

Gary
 
Where are you located? Is your boat wet slipped or trailered? If it's wet slipped, did you just put it in the water and observed this problem for the first time? Has the boat always run this slow?
 
We bought the boat in mid December '06. Since then it has been wet slipped behind our house. Water is fresh to brackish. Salt content quite low. We had the bottom cleaned last week, not sure how good a job the guy did. I have noticed some built up on the lower unit and the props are a greenish color instead of clean stainless steel. Shortly after we got it, we had it up to about 4200 rpm with a top end around 38 knots. But recently 29-29.5 knots is the best it will do and that's with the unit trimmed up and under half a tank of gas.

-chazaroo
 
Is it carbed or fuel injected?
 
So, from what you have posted, originally at 4200 rpm it would do 38 knots. But now, it will only do 3900 rpm and 29.8 knots.

You can divide the rpm by the knots. In the first case it took 110 rpm per knot. Now it takes 130 rpm per knot. Seems to me that something is holding the boat back in the water, or the prop has too much drag and just can't move the water anymore. And whichever it is, there is more load on the engine and it just can't get to the higher rpm with all that load.

Although you appear to be over-propped to begin with, it suggests to me there is nothing wrong with the engine, the problem is 'why can't the boat move?' Maybe the prop is just too fouled. Maybe you are dragging anchor or rode through the water (you'd probably hang it up in the prop if this were the case). Maybe the bottom is still fouled, or maybe the boat now weighs much more than it did.

Maybe your trim tabs are all the way down, and you can't retract them. But I doubt they could have that much drag.

Just some thoughts.
 
The boat is carbed not injected. Could the carb be the problem? The engine starts easily and sound good. No miss detected and plugs, wires, points, cap, rotor were all replaced in February. As for being over propped...I don't know. The boat came from the factory with a Bravo 3. I'm going to take it in this week to have everything looked over. If the bottom is fouled, we'll be able to tell pretty quickly. That would certainly be an easy (read inexpensive) problem to fix.

Chazaroo
 
Well, you said it worked great in Dec. and now it won't pull to the desired RPM. What has changed or happenend between then and now... Seems there was a tune-up. I'd have them check the timing again, and possibly the plug gap. Not saying this IS the problem but it would certainly be worth investigating. (to me anyway)
 
Good thought about the timing and plug gap. The only thing that makes me doubt it is that the engine sounds fine. No missing, popping, sputtering, etc. It just won't get the rpms up. I'm taking it over to the marina today to have them take a look. Their first guess when I explained what was happening was that the bottom must be fouled. We'll see.

Chazaroo
 
Dave,
Throttle opening is one I hadn't thought of. :thumbsup:

Gredmer,
Not sure about the Viagra. Does it get added to the engine oil or to the drive? :huh:

Chazaroo
 
Got a voice mail from the Marina, they cleaned the bottom and said they had the boat up to 38 mph and 4100 rpm. I think that's still a little low but a whole lot better than the 29knot max I was getting.

Chazaroo
 
I just got back home with the boat. They changed fluids and cleaned the bottom. It's running much better. I had it up to 4400rpm (according to the tach) GPS speed reading 33.9 knots or 38mph. That's with one person 170 lbs on board , 10 gallons of water and 70 gallons of fuel. I think that's about what it should be. So I guess it's safe to assume the bottom was the problem. What do you all think?
 
Sounds like you solved 99% if not all of the problem with a cleaner bottom. Congrats.

Now you have to get the $ back you paid the earlier guy to clean her. He obvously didn't deliver.
 
Yeah. I sent the guy a letter expressing my feelings regarding his out-of-line price for bottom cleaning. Now I find he did a lousy job as well. Isn't that always the way? Oh well, boat's running great. Life is good.

-Chazaroo
 
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