Increased RPM during engine flush (spontaneously)

[Ivans]

Is there any reason why my outboard rpm increases during engine flush? At first it goes normal then the rpm goes up. Turned off and back on the outboard went normal then up again

This happened after first 5 min or so of engine flush after fishing session. First time engine started was normal

Any ideas
Thank you

[ducky]

Does it happen when warm too?

Could be some form of auto choke?

[Tackleberry]

Is this a fuel injected 4 stroke

[repspec]

What engine?

Does it do this normally in the water?

Did the motor sit for extended periods of time without been run (6 months +)

[skronkman]

Could you have your fuel tank breather closed off, fuel line disconnected or very low fuel in tank while flushing? If this happens your motor will run fine until the carby bowl (assuming your motor has one) starts to run dry due to the fuel pump not being able to draw fuel. This will lean out the fuel mix and cause the rpm to race, usually followed by motor surging several times and then stalling.

If your tank is low on fuel and your boat/tank is on an incline away from the pickup this can happen, as in flushing the boat while on a hill.

[cobby]

What engine?

Does it do this normally in the water?

Did the motor sit for extended periods of time without been run (6 months +)

If I remember right its an early 00s 115hp carby 4 cylinder mercury

[repspec]

If I remember right its an early 00s 115hp carby 4 cylinder mercury

If its one of these engines, they have a 2 stage carby set up.
Basically at idle, the top 2 carbies are running, once it gets above a certain revs (around 1200rpm) the 3rd and 4th carbie kick in.

When the motor is on flushers, there is no exhaust back pressure. Back pressure helps slows the idle speed down (effectively)

Normal for one of these motors.

The other thing that can happen, is the throttle link rod bushes break. Quite common. This could jam the throttle on/ make it rev higher

[blacklab99]

Hi,
I've had 2 of these engines, the 115 and the 125 models. There bullet proof, the 3 and 4 cylinders kick in around 1800-200 revs so this wont be an issue on idle. They do run rough, especially the transition period between 2 to 4 cylinders. They run an unbalanced crank, so the engine is limited because of this, can't remember at what rev's the 115 was limited too, but the 125 was limited somewhere around 5500, from memory. The 125 was permanantly converted to full time 4 cylinders, with the low down torque very impressive and anything over 3500-4000 revs, you needed shares in shell !!.
Getting back to your issue, The carb set up is quite finicky, DON'T let ANYONE adjust the linkages or carb set up, unless they absolutely know what they are doing, otherwise problems will be a standard feature. These designed Merc's finished in 2005, so not many mechanics have a clue in servicing and setting them up properly. Linkages, lines etc would want to be checked out, but if idling in the water has the engine idling normally, then as repspec said, its a back pressure issue. I used to get a guy that was work shop foreman for Mercury to service mine, he knew this model inside out and was facinated that my 125 was PROPERLY converted, as they were experimenting with this when they were discontinued, he used to operate by keys road, but I see he's not there now.... I may be able to dig his number out should you need it........

Col

[Ivans]

Hi guys sorry been busy with work. Hectic close to xmas. Then i forgot. Havent been out for 2 weeks

Outboard is 2002 mercury saltwater 115 2 strokes

It doesnt happn when boat on water.
When i turned off the engine and turn it back on, it sounds normal again

[Ivans]

If I remember right its an early 00s 115hp carby 4 cylinder mercury

If its one of these engines, they have a 2 stage carby set up.
Basically at idle, the top 2 carbies are running, once it gets above a certain revs (around 1200rpm) the 3rd and 4th carbie kick in.

When the motor is on flushers, there is no exhaust back pressure. Back pressure helps slows the idle speed down (effectively)

Normal for one of these motors.

The other thing that can happen, is the throttle link rod bushes break. Quite common. This could jam the throttle on/ make it rev higher

So you saying nothing to worry about?