Yamaha outboard hesitates

[Gert van zyl]

I have a yamaha outboard motor 100 (FET) 4-stroke since 10hrs on it. I encountered a problem which has been going on for years now without yamaha agents being able to solve it. We do lot of water sports and skiing. The motor start and runs fine without issue. Idles @ around 5000-6000 rpm. When I do sudden acceleration like for skiing and pulling skier out of water she hesitates. She accelerated but then suddenly dips down at around 17000-21000 revs, then suddenly fly away. Sometimes she will stall but not always. I tried a lot of suggestions and does not know what else to do. Any advise?

[99yam40]

looks like you put too many 0s in the RPM.

I am guessing this is a injected motor is that correct?
if so monitoring pressures while this happens may tell something.
at least you would know if it stays in spec or not.

on some motors the pressure regulator increases fuel pressure under these kind of conditions and also increases injector one time or fires injectors more to increase fuel.

I have no idea what a F100 is suppose to be doing.

[boscoe99]

What is the engine ID? Begins with the number 6.

Is this a fuel injected or carburetted model? I am guessing the latter but ...

How quickly are you advancing the throttle? Are you jamming the throttle handle forward or are you coming up on power smoothly but steadily?

[rodbolt17]

does not matter how you throttle up.
I slam my F150 and I slammed my 130.
if adjusted and operating correctly that is how they are supposed to run.
having never seen a fuel injected F100 I cannot comment on it.
having worked on hundreds of carbed F75,F80,F100 motors I can.
typically that bog is either a lack of fuel pressure, an improperly routed acceleration pump hoses or a carb that needs a tad richer mix and or the float height is incorrect.
throttle plate adjustment is about as critical as correct float height.
the carbed version uses an odd accelerator pump.
this creates an even more pressure differential between the fuel in the bowl and the venture area.
that is why throttle plate adjustment is so critical and can ONLY be done with a 4 channel manometer.

[boscoe99]

does not matter how you throttle up.

On a mis-adjusted motor it can.

[99yam40]

On a mis-adjusted motor it can.

this is true, but he covered that after that statement.

I would like to know what kind of fuel distribution this motor has since it sounds like it is in some other country

[99yam40]

all motors need to be a little rich at idle to help transition to open throttle

[boscoe99]

I love these mysteries. Trying to solve a problem from a distance when we don't know what model motor it is.

Over on some other sites without the model and serial number being provided they will refuse to help.

Looks to be an EFI model. https://www.marine-tech.co.uk/new_ou...ha-f100-fet-x/

[99yam40]

Hopefully he will come back and let us know a little bit more soon

[boscoe99]

Similar to our F90 and F115.

[TownsendsFJR1300]

I love these mysteries. Trying to solve a problem from a distance when we don't know what model motor it is.

Over on some other sites without the model and serial number being provided they will refuse to help.

Looks to be an EFI model. https://www.marine-tech.co.uk/new_ou...ha-f100-fet-x/

Prime start AND Fuel injection on the same engine??

How's that work??

[boscoe99]

PrimeStart is Yamaha's term for any automatic cold start fuel enrichment system.

[99yam40]

I am sure It is just saying that it will automatically enrich at cold start and run a little rich during the warm up.
probably injector on time adjusted and/or pulsing all injectors at start up to get extra fuel into it.
kind of like choking a carbed motor

[TownsendsFJR1300]

PrimeStart is Yamaha's term for any automatic cold start fuel enrichment system.

I know what Prime start is and it's used with carbs.

The engine (per the highlighted yellow above) it's Fuel Injected and WOULD NOT use Prime-start (not needed).

[TownsendsFJR1300]

I am sure It is just saying that it will automatically enrich at cold start and run a little rich during the warm up.
probably injector on time adjusted and/or pulsing all injectors at start up to get extra fuel into it.
kind of like choking a carbed motor

Well, it's not accurate in any event. You can't have both systems on the same engine.

It's one or the other..

FI (as you know), doesn't need a choke, or a Prime Start solenoid, it's all computer con*****ed ..




Walleye1, did you get a response from admin?