yamaha 25hp 2 stroke dying

hi i have a reasonably old 25 hp 2 stroke which upto now has been great but am now getting problems with rough idle and stalls when i drop it back down to idle or try to accelarate away after dropping it back it wont start again unless i prime the bulb on the fuel line then will run fine at high rev but will still do the above if i drop the revs i have cleaned the carb and changed the plugs... is it likley to be the fuel pump diaphram ???? many thanks

What year is it? Ethanol in the fuel today eats away at everything if it wasn't designed for E10

i dont know how to age it could you help ??

Maybe this wil help if you can find the serial # on the engine... Found this online...


There is no user information contained in the Yamaha outboard serial number other than identification of the particular engine to which it is attached. All information for the Yamaha is contained in the model number, i.e...... F6ESRY
F = Model Designation (Four Stroke)
6 = Prop Shaft Horsepower (6 HP)
E = Trim & Tilt / Starting Method (Electric Start)
S = Shaft Length (15")
R = Control Method (Remote Control)Y = Model Year (2000)


Read more: http://wiki.answers.com/Q/How_do_you_read_Yamaha_outboard_serial_number#ixzz1uz7v6ePQ

i have the model number and engin number are these what you need as i couldnt work it ok lol

model 25DM
engine number 695L 319 505

On the plate where you found the serial number there is a letter below the line in which the number is, either in the left or right corner. It may be difficult to see but with good light and maybe clean glasses or magnifying glass it should be visible. When you have found it compare it to this table: http://www.marinshopen.se/Motorer/OmMotorer/Yamaha/Fastställårsmodell/tabid/366/Default.aspx
It is in Swedish but that shouldn't pose problems. I would bet on 1976-1980. Let us know what you find out.

I had a similar problem on my 1986 25hp. I wasn't going to play guessing games so I replaced the fuel pump, easy fix, gas filter, easy fix, I replaced the primer bulb because mine was old and beginning to dry out and I replaced the gas cap on the tank because it was pretty rusted and I think may have been causing a vacuum in the tank, preventing a steady flow of gas. I also started using Stabil Marine gas stabilizer since I was told that it helps with the performance of today's gasoline in marine engines. Don't know which one of these fixed the problem but the problem is fixed and the motor runs great.
Good Luck