What would cause my 320 fiesta vee to struggle getting on plane

dljboats

We purchased this summer a 2005 320 fiesta vee with twin 5.0 mercruiser engines. Ran great the first month. Then one day couldn't get over 25mph, and the following day could not get over 13mph. Could not get on plane at all.our mechanic did a complete tune up on both engines and did find a fuel line leak. He replaced the fuel line. Took boat back out and still no change. could not get on plane at all.he has now blown out the fuel lines and did find some gas in them . Took boat back out today on a flat lake, was able to get on plane but it was a struggle. Never got over 24 mph... any ideas

LaRea

Welcome to the forum.  Is the hull clean?  Bottom growth will kill performance.  Depending on where you are, you might need to have the bottom cleaned halfway through the season.  

Liberty44140

And did he do fuel filters in that tune up or just plugs, wires, cap and rotor?

dljboats

2 people were on board. We had boat lifted yesterday and it was clean. We had it  bottom painted after we purchased it, that was beginning of July. Yes fuel filters were  replaced  in tune up.

LaRea

Fuel, air, spark.  Do the engines backfire when you hit the throttle?  That could indicate water in the fuel.  

Are you getting any unusual beep alarms when you start the engines?  Beyond that, I'm running out of suggestions.

johnrenwick

You might have something stuck on the outdrive. I had the same problem and a passenger suggested a hard reverse. I came to a stop, put the throttle in reverse and gave her the gas for a short time. Before I swamped, I stopped and resumed my forward course. All was fixed. Must have been something I picked up in the river.

zaverin1

Compression check?
both engines able to hit rpm ?
how old is the fuel
or recent fill
up.
gas tank air vents checked?
if props are clean, couplers are good and compression is good start looking at ignition and fuel 

zaverin1

Oh and make sure drives trim proper up and down 

dalek

Next time you are out, try accelerating a little with one engine only, and then the other, to see if they respond similarly. If you have one good engine and one weak engine, it is not always obviously apparent.
 As you are moving and water flows over the propeller of the weak engine it may effectively partially assist in powering this motor and the engine RPM may match the good engine, even though the weak engine is totally gutless.

rasbury

Diesels?

zaverin1

No propane 

reneechris14

??injectors?? Does a motor pop(small back fire) when giving to much throttle. 

scotteboy1

Has anyone heard of a load limiting sensor? Supposed to be a safety feature that won’t allow your boat to exceed certain rpm’s but will allow you to move slowly.

Handymans342

Yes we have

Black_Diamond

Your mechanic should be able to read the engine code faults and if it is going into guardian mode.

LaRea

@scotteboy1 -- "Load limiting sensor" is a general term.  In modern engines, the engine computer uses all available sensors (oil pressure and temp, coolant temp, etc.) to find potential problems.  If something is wrong, the computer will reduce power to avoid damage.  (Also known as "guardian mode")