Really poor engine performance

pstew96

pstew96

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Dec 4, 2003
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12527
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So, it takes forever to get up to any acceptable speed, and when it does, it tops out at about 23 mph WOT, last year it topped 33 mph WOT, it sounds like its hesitating and surging, probably not noticeable to passengers, only enough for the driver. I filled the gas tank before I put it in the water, it takes 70 gal, I put in 60. Changed the oil and gas water separator and stored it in a heated warehouse over the winter. What could it be, had this boat less than a year.
 
You might get some good suggestions if you include some more info. Make, model, year boat, boat length, engine size, drive type, etc...
 
Its a 2004 Maxum 2400 se, its got a 5.0 merc and Alpha drive.. only 110 hours on it.
 
Make sure all the spark plug wires are seated. I had this problem with a boat I had with a 5.0 Merc.
 
Use up 60 gal again and then fill it. See if it's better on the next tank.
 
Oh yeah, of course this is assuming the bottom is clean, the prop not fouled, and any tabs are in the proper position for planning speed.
 
Even though there is only 110 hours on the engine the plugs may be fouled.
If the poor performance continues try swapping them out if you haven't already done so
 
Electronic ignition???

Carbed or fuel injected??

Sounds like fuel problem...
 
So I took off the fuel water separator, found only about 1 drop of water, checked the plugs for snugness, cleaned the carb and flame resistor with carb cleaner, I haven't gotten to the carbs filter yet or the aniti siphon valve, the prop is the same one as I used last year when it ran nicely. The fuel looks and smells fresh, but the boat as I tried again last night is sooooo slooow, it takes forever to get to 24 mph at WOT.....I play with the trim and it does influence it, but the top speed is 24 mph...
 
Just splashed after a winter of indoor storage... I was wondering if it picked up water weight somewhere in a double bottom/inner hull. Stored indoors, probably not.

Good idea to check the carb's fuel inlet filter, for sure. In theory it shouldn't have anything to trap, after the MerC OEM filter/separator, but still worth a shot. Be sure to stabilize the big "nut" part of the fitting while you work the fuel line fitting.

Electrical problems are Such Gremlins! Make sure battery connections are clean and tight. Also, if it has a red "Perko" battery switch, that those connections are clean and tight. Work the switch a number of times to scrape its contacts. I'll admit that battery/terminal/switch problems usually cause more severe problems than you're seeing. Still, it's easy, free work to make sure they're OK.
 
Make sure nobody borrowed your prop over winter
 
Did you winterize last year or skip it due to the heated garage. Chances are it is fuel related. You may have gotten an algae bloom in your fuel that is clogging the upper jets in your carb. I had the same issue one year. Boat would idle fine but as soon as i put a load on it it felt like i was pulling Oprah on one ski. Upon rebuilding the carb found a green slime in there. Mechanic said it was the result of the ethanol....
 
quote:
Originally posted by sunshinedaydream

felt like i was pulling Oprah on one ski

Click to expand...


Now THAT is Word Picture of the Week!
 
Haaaaa! Oprah ! that is quite a picture!! I am doing only about 3500 rpm at WOT and 23 -24 mph.....
 
Last time ours wouldn't get to WOT RPM, we we had a loose plug wire. Does the distributor have any form of mechanical spark advance? I doubt it does, but if so, are the weights and springs free to move as RPM increases? How "electronic" is this engine? Could it be in "limp home" mode as a result of some fault being detected?
 
quote:
Originally posted by jtybt15

Rochester carb?

Click to expand...


Don't know, will check it this weekend. My friend says there may be a strainer inside the gas tank thats clogged, anyone ever heard of this?
 
they all should have a strainer and yeah they can get clogged.
 
Yes, a fuel strainer can get clogged, but would probably show in other ways- surging, cutting out or bogging when you push the throttle past a certain point. The odds that it would clog up just enough to limit your acceleration and top speed without any other symptoms, are IMO pretty slim. Still worth a check, tho.

The motor's 11 seasons old. Has it ever had a FULL tune-up- plugs, cables, cap, rotor? Base timing and timing advance should both be checked. You've changed out the fuel/water separator, so continue on with the fuel system and check the carb inlet filter (if it has one- my Weber/Carter carbs don't), the anti-syphon valve and filter screen.

My guess is once you've performed all the basic routine maintenance you'll be back in business.

My.02
 
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