hesitation/stalling on slow acceleration

[jdm313]

I'm having a minor problem with my 2004 Yamaha F150 (4 stroke with EFI). It seems to idle fine and shifts into gear fine. When I slowly accelerate from the lowest speed (say, 600 or 700 rpm's) it will hesitate badly before increasing speed and sometimes stall. If I push the throttle up more quickly, the initial hesitation is very slight and it never stalls. The engine accelerates and runs great once it gets past about 900 rpm's; the problem only occurs when I slowly accelerate from very low rpm's. I replaced the spark plugs (the old ones looked normal and didn't really need replacing) and cleaned the fuel filter, and that had no effect.

I'm not too knowledgeable about engines yet but like to fix things myself. Any ideas about what might be causing this problem would be greatly appreciated. Thanks!

 

[Striper15]

Re: hesitation/stalling on slow acceleration

I own a 2006 Yamaha 25hp, 2-stroke that experiences the same condition as you. Must be something in common with both 2 and 4 strokes??

I just ordered a set of Boyesen reed valves (not used on 4-strokes of course) in hopes of correcting the problem. With a 4-stroke, it may be a timing/advancement problem??

This is my first outboard, so I am very much a rookie and would love to hear what others have to say.

 

[rodbolt]

Re: hesitation/stalling on slow acceleration

striper.
your problem is not reeds. its going to most likly be the carb and/or the link and sync. take it back and have it fixed.

jdm
dunno on yours. mine does the exact same thing, now that it has 10 hours on it I guess i will take it in and let the lead fool at the shop take a look at it.
oh, that would be me .
anyway if and when I get around to finding out why my F150 does the stumble/stall when throttling up very slowly from idle Ill post it.
thats why my other boat has a 175 E-TEC. I wont ever work on the E-TEC .

 

[jdm313]

Re: hesitation/stalling on slow acceleration

rodbolt,

It must be annoying to have this happening with only 10 hours on the engine. I bought mine used this past spring (270hrs at the time) and didn't experience the problem until September, although maybe I just didn't notice it. Do you think maybe the idle speed could be a tad too low? I haven't checked mine yet. I just read a post from another website where a guy who was having the same type of problem adjusted his idle rate up to 750 rpm on the F150 and that resolved it. He was told by a Yamaha rep. that the F150 performs best at the upper end of the 700 +/- 50 rpm range that the manual suggests.

If my idle speed turns out to be low, how would I go about adjusting it? The service manual isn't explicit about what part controls the idle rate. I'm guessing it's either the throttle link/cable or the throttle position sensor, but I haven't investigated how those things work yet. Thanks for your help!