might be a prop pitch problem....someone may have put on a couple props with too high pitch to try and get a little more top speed.....but that can result in 'lugging' the engines and not allowing them to reach the WOT rpm range.....a dirty hull bottom can also significantly produce drag on the boat which will cause the engine rpm's to not reach the WOT range....if water was allowed to sit at a high level in the engine room while it was not active all those years it could be the stringers and maybe transom are full of water causing a lot of extra weight and drag.....

good luck....
cliff

 

Sounds like a great boat.

 

You’ve changed a lot already so it might be something abstract. Did you pull the drives? Since it say so long maybe the rubber exhaust flappers dried out and flew down the Y pipe. They get stuck at the transom and add a bunch of back pressure reducing RPm and power.

What temps do the motors run at, and what speed are you doing when you’re at that 2800/3200?

 

Drives were taken off and sent out for service. New water pumps and impellas and presure tested. Put back on with props that came with it and owner said he never had a problem with them befors. Engine room is dry and solid. Spend 7 weeks cleaning it and has new bottom paint so no drag. Temps on both are 170

 

it sounds like you are doing the right things and have a good knowledge of what you are doing and why....I have heard of someone accidentally installing a 6 cylinder rotor button in the distributor of an 8 cylinder engine and having all kinds of issues....I believe the rotors for both the 6 cylinder and 8 cylinder engines look identical....the only difference being the number of teeth of the rotor to produce the correct 'hall effect' through the ignition sensors inside the distributor cap.....when you said you changed the 'ignition sensors' are these the ones inside the distributor cap?.....

have you checked the ignition timing?....

are both starting batteries in good condition?.....EFI engines like to have a strong and consistent voltage in the ignition system.....

cliff

 

As Ryan asked, how fast are you going at 3200 RPM? Maybe a tach problem?

 

The one that attatches to dist. At 3200 im doing approx 12-15 mph. Boat just stands up. Bow will not drop

 

Original engines could be tired after 20 years. Engines don't like to sit for 7 years either.
Compression test might not be a bad idea.

 

just for 'peace of mind' I would verify the size and pitch of the props are correct for that boat and drive system....just because the owner said he 'never had any problems' doesn't mean maybe a previous owner before him had changed the props.....the size and pitch of the props should be engraved on the props....

it sounds like you did not have a survey done or this performance issue would have been discovered prior to purchase....

cliff

 

No survey. Will def check on prop size and pitch. Motors have under 400 hours on both. Compression test was done and is fine. Gonna try the timing. Thinking one motor lagging ot out of timing and dragging other down

 

those engines probably have the Mercruiser 'Thunderbolt V' ignition system...you may already know this but you have to put the system into 'base timing mode' before you check the timing....

I had a lot of problems in a previous boat with the TBV ignition system...I eventually just replaced the whole system with a Delco marine ignition system that worked perfectly....

cliff

 

They do not have the thunderbolt. Gonna see tonight with timming.

 

good luck....keep us informed on your progress....there is a vast amount of knowledge on this forum...I'm sure eventually we collectively can figure out what is going on.....

how old are the starting batteries?...

cliff

 

I had a very similar problem with my 210 SD with a single 5.0L EFI. I changed all the same things you did and it would rev out to 4500 rpm on muffs but couldn't get up on plane in the water. I finally took it in to a marina to have them look over it and they called me in the afternoon and said come and get it. I thought maybe they did something with the timing not advancing and asked what all they did to it, but he just smiled and said that was their secret but it is fixed now. All they would tell me was that they put a new Turning Point prop and hub on it and it runs fine now. The OEM prop was a 14x19 and the TP prop is a 14.25x17.

 

Thanks. Props are fine and in good shape. Gona put a fuel pressure guage and vacume guage on it under a load and see. Then Gonna put a timming light on it and see if it is the timing not advancing. Boat is new to me so when i got it anything that was old was tossed and new was installed. Batteries are about 3 weeks old

 

...Props are fine and in good shape...

Jeff, do not discount the props. Even perfect props that are the wrong size, pitch or cup could be part of the problem.

You also mentioned doing cap and plugs etc. Go back to some basics and also verify the wires are running from the distributor to the proper plugs - Its a simple check and can cause similar problems too.

-Kevin

 

Kevin. Thanks. That is def on the list tomorrow to check. This site is very good with kmowing their stuff. Everything discussed is a possible gremlin

 

You said the motors are running rich at an idle.
Something is telling the ECM to richen the fuel mixture IE-Map Sensor/Engine coolant sensor/dead cylinder causing low vacum or a vacuum leak.
Have you checked the fuel pressure throughout the RPM range when under load .
Did you replace the fuel pressure regulators and fuel coolers when you did the fuel pumps.
I would get a scan tool on the engines and read the parameters of the sensors. And check for codes.
Google the repair manual theres plenty of sites that have them in PDF for free.
The specs for the sensors and fuel pressure are in the manual as well as trouble shooting trees.

 

How was the boat stored for 7 years? Is it possible it has taken on extra weight during that period. Not familiar with your model myself but am sure many others on here are. A pic of it in the water may help to identify a weight issue if scales aren't an option. Another thought might be to confirm tabs stay down while trying to get out of the hole.