F100DETL yamaha outboard

[madharchod]

iam having full speed problem with these engines

[madharchod]

problem with f100

i cant get them to stay running on full throttle as they die out ,need help

[rodbolt17]

typically its gonna go like this.
test spark.
test compression,leakdown would be even better.
fix fuel system.

[madharchod]

thanks for that rod

i have tried the sequence you directed ,still no good
it runs and idle perfect,the sparks are good,compression id 150psi even in all cylinder ,and the fuel line seems good as the fuel is going alright
what happens is when i try and give more throttle it goes up and then dies out ,this is for one motor.
the other one is not going full throttle ,at goes up to 3000rpm and stays there or dies out too,then i have to pump the primer and start again and it starts again
don't know man ,need help

[rodbolt17]

your going to fix the fuel system.
if by pumping the primer you can keep it going or its needed to restart it indicates a lack of fuel in the bowl.
this is typically caused by a weak fuel pump,air leaks in the line or a restriction between the fuel pump and the liquid in the tank.

[madharchod]

hi rod

tried doing that,one engine has improved a little bit but the other ones is spattering and can hear weird noise and then the engine stops ,start again it goes again and no noise but dosen't go full speed

thanks

[99yam40]

Just exactly have you done?
Saying you tried that does not mean much

[madharchod]

hi rod

i have changes the fuel line ,new ,water separator filter new, cleaned the VST
changed the oil new ,new NGK spark plugs,still the problem remains

[99yam40]

this is typically caused by a weak fuel pump,air leaks in the line or a restriction between the fuel pump and the liquid in the tank.

Did you look at fuel pumps or measure the pressures and vacuum to see if there are restrictions or problems with pumps?

[madharchod]

hi there'

i think i will need to replace the fuel pumps as there was some liquid in the underfloor tank ,and no i haven't checked the pressure . think i will do a complete renewal of items ,like the fuel pumps and the injectors,ignition coils ,engine control unit,wire harness assy, and thermosensor,what do you think ,and have you got all these parts and will they fix my problem
thanks

[99yam40]

You need to start testing things to see what the problems are, not just throw parts at them and hope

[madharchod]

hi there i have had a good look at some of the wires especially the battery cable they have gone black ,looks like burnt and also the fuel pump is a bit sluggish and on checking the injectors it look like they haven't been changed since 2006 and these motors are only 1300hrs old ,as you say testing i don't know how ,so i think by replacing all these parts will get me going for now until i save up for two new motors
thanks

[99yam40]

A service manual will tell you what you need to test things and how to test.

Or you can take it to someone that knows how and has the equipment. Sure beats buying parts that are not a problem

Even injectors can be tested if you send them off to the right places

[rodbolt17]

if the fuel pump,mechanical, is catching air or the inlet side is restricted.
it will sound just like a collapesd lifter in an old chevy motor.
will give a loud tapping noise.

[madharchod]

hi there,

i have done most of the things required ,but haven't changed the fuel pump,as i took it for a run again today it takes off for about half a minute at about 4500 rpm and both engine dies out ,i tried starting again ,one engine started but would not get speed over 2000rpm and the other one just didn't start until i had a flat battery ,and i had to come back home