DF115 runs at 10 MPH full throttle @ 4000 RPM

[Razinkane]

Hi, My 2003 DF115 starts fine and runs good at slow speeds but tops out at 10 MPH and 4000 RPM at WOT. I changed spark plugs, marked my prop hub for slippage, bypassed fuel/water separator and gas tank with fresh fuel by connecting to the fuel pump. Any ideas??

[mgilden]

My friend had the same problem on his Yamaha it ended up being a fuel sensor

[Harper]

You don't say what kind of boat, but I'm going to assume that your boat has a planing hull. You should be able to get on plane at 4000 RPM. That you're not getting on plane and going only 10 MPH, leads me to believe that the boat might be the problem. It's possible you're overweight due to water in the hull, the bilge, or whatever and just too heavy to get on plane. I've seen it before, on a yammy 115 2 stroke. The boat was so heavy, and there was so much load that the motor acted like it was bogging down, and wouldn't turn any more RPMs trying to push all that water at that low speed. Once my young brother fixed his bilge pump and emptied his bilge of all that water, everything worked as it should. There had been nothing wrong with the motor.

[catacom225]

you sure its not in limp mode?

[mgilden]

Actually my friend's motor was not a fuel sensor but a throttle valve

[Razinkane]

Harper- it’s a 17 ft prosport all fiberglass 1700 lb bilge is working fine.

[Razinkane]

I did have this same problem last year when I put it in the water in august but it cleared out after a few runs. FYI- on Lake Ontario. Fresh water. boat stored longer than it’s in the water on a yearly basis.

[Razinkane]

How do I determine if it’s in limp mode?

[Razinkane]

Also- when pumping my primer bulb my fuel filter will fill up about 1/3. In a short while the fuel drains back out. Shouldn’t it hold since the primer has a valve to prevent fuel from draining back down?

[briscoe]

I think you answered the mystery. If your fuel filter is not full at WOT it sucks. You need a new primer bulb. Easy breezey

[Razinkane]

I’m saying that the fuel filter won’t hold gas when off. Not at WOT.

[Razinkane]

And I ran a separate line with a gas can to the fuel pump with no improvement so the primer is not the culprit

[Harper]

I'm still wondering how you could turn 4000 RPM and still only go 10 mph. I could understand a problem with the motor that wouldn't turn over 2000 RPM and go only 10 mph, but shoot, my 2800 lb. 20 footer will plow along at 10mph when turning 1500 RPM. That with an 18½" pitch.

[Razinkane]

I wish I knew!! Today I tried changing a fuel line that looked bad but nothing improved. Any additional ideas??

[redlowrey]

I did have this same problem last year when I put it in the water in august but it cleared out after a few runs. FYI- on Lake Ontario. Fresh water. boat stored longer than it’s in the water on a yearly basis.

If you had the same problem before and it came good it sounds like you may have a cyl dropping out, possibly a sticky injector or coil tracking and only effecting one cyl, have you checked and made sure the high pressure fuel filter is not blocked.
you could have high resistance in one coil lead breaking down under high load, pull the leads off the plugs and check the resistance of the leads between 1 and 4 and 3 and 2 pull the plugs and note the color of the porcilain and the cyl they come out of and report back on the forum.