Outboard won't run full throttle unde load

[fruitspice]

Hi guys am seeking help with my 1997 Mercury 2stroke 9.9hp outboard it runs great in idle and reverse but as soon as you click into forward as you increase speed it'll kick in but then start to decrease speed after about 10 seconds but sometimes will run fine for 10 minutes or so but then it reduces its self to about a walking pace !! The motor has been serviced including carbs clean and has had the trigger replaced and new Impala ! I've tried a different fuel tank and line which it ran great and thought id found the issue until it went back to shit !! Am really stuck

[Geoff]

It could be a few things so a process of elimation.

I see you have had the impella replaced but is it pumping a good stream of water from the tell tail??.

Is the water warm or cold when the problem occurs??.

Have you checked the thermostat to see if is working properly or perhaps there is some rubbish that can be seen when the thermo is removed.

Some motors have a control device that if the motor becomes hot it reduces the rev's so not to overheat.

If your motor has one of these devices it may be faulty.

Finally , when the motor begins to fade pump (squeese) the primer bulb. If no change then it's most likely a temp or electrical problem.

Geoff

[fruitspice]

Thanks Geoff it does pump a good stream of water but I've never felt it to see if it's hot or cold so will have to check that !! From my research I don't think my model has guardian mode, but the issue can happen within minutes of the motor starting so it'd still be cold but your right if the thermo isn't working that just could be it, but when started during flushing it can happily run as full throttle but can't under load in the water

[a boat]

That engine will have nothing to protect from overheating so it will not be that. It sounds like ignition but if the engine revs in reverse I can not see how going into forward will cause it not to. Make sure the linkages are correctly set-up and you will need to check for two strong spark when it starts to die and also choke it with the plunger to see if it picks up and if so then it will be fuel related.

[fruitspice]

Thanks Huey while its idling if you pull the chock it almost snuffs out

[a boat]

That's normal and I mean when you have asked the engine to do some work, either gear with throttle open. If is it starving for fuel by pulling the choke plunger out it injects more fuel and if it picks up slightly then it will be fuel related-I hope they set the float height correctly if they did remove the clean the carby. Also the ball in the choke plunger-under the spring can cause problems on there 9.9/15HP US Merc's.

[The Iceman]

Might be a silly answer but did you loosen the breather on the fuel tank

[austral]

I had the same sort of problem with my 15hp Yamaha. it turned out to be the propeller bush. which is a rubber grommet type thing that holds the prop onto the shaft. a new prop did the trick.. got mine from solas.

hope this helps..

[fruitspice]

Hi Iceman yeh I had the breather quite loose, Hi austral is Impala another name for prop bush ? If so then it's been replaced

[fruitspice]

Hi Geoff the water coming out of the spout is luke warm

[a boat]

Hi, it is "impeller" and if you do not understand the difference between an impeller and a prop bush I think you will be in over your head and I would be surprised if, from what you are describing, it has anything to do with a prop bush, because a slipping bush happens in both gears and allows the engine to rev, just like a slipping clutch in a car. What does the person who you say serviced this engine including the carby say because he most likely did something wrong.

Cheers,

Huey.

[fruitspice]

Sorry brain fart impeller lets the water flow out of the spout right ? and the prop bush allows the prop to spin on either gear ? No had an old outboard that the bush broke while out fishing was a long row home lol the guy servicing thought it was the trigger or the cdi box, tested the trigger it wasn't responding correctly so it was replaced and made no difference ! I think he's a bit baffled ! I've now taken it to a local Mercury repairer but even they thought it sounded confusing but they'll be looking at it on Wednesday

[Geoff]

Hi Geoff the water coming out of the spout is luke warm

OK , that means the tell tail is after the water passes through the motor ( some are before).

If it's only warm then it's not a temp or water flow problem.

If pumping the primer bulb did not make any difference then I suspect it is electrical.

Did you try running the motor in a tub of water to avoid launching the boat & to try & simulate the problem at home.

Geoff

[fruitspice]

I never ran it in a tub, only ran out home with rinse kit and it had no dramas, but I understand that it's under no stress with the flush kit

[austral]

so did the engine rev really high even though you were only at walking pace????

[fruitspice]

No it it reved low equal with the output !! Had the call back today from Mercury as usual it wouldn't play up for them it took awhile but finally it did and they said they are certain it's the cdi box ( switch box) and sadly a whopping $580 as a total to fix

[a boat]

Why is it only doing it in forward then, if it is in fact a faulty switch box, I guess the trigger was OK then, it would stop in either gear or in neutral-which you said in the first post it was not. Something does not add up and that is expensive for a switch box.

[fruitspice]

Yeh was thinking it was expensive to Huey, but I don't know how to install myself so have to pay the price [emoji20]

The trigger had already been replaced ! Just hoping this is the end as I have the money to keep this up !! Thanks again to for your advise and help

[a boat]

Your call then and as long as you are happy that is the main thing, but it takes 10 minutes to swap a switch box-pretty much plug and play. I still do not see how it only happened in forward, but can not comment anymore without seeing it muck up.

Edited October 15, 2014 by Huey @ Huett Marine

[deek]

Yeh was thinking it was expensive to Huey, but I don't know how to install myself so have to pay the price [emoji20]

The trigger had already been replaced ! Just hoping this is the end as I have the money to keep this up !! Thanks again to for your advise and help

Fruitspice,

Just take it to Huey, he'll be able to take a look at it for you.

Cheers

Deek

[fruitspice]

I'm on the Sunshine Coast Huey where are you ?

[antonywardle]

Between Sydney and the Central coast in Cowan

a wee way from you

[spaners]

The problem is as a qualified mechanic we are asked what the fault is by a layman {no offence intended} and often the description of the fault from the layman is incorrect and that is why you will see 10 different posts from 10 different people of what the fault is.I would not be mucking around with a outboard engine if you cant do or do not understand the basics in mechanics or electrical.If you don't know how to pack bearings,use a multi meter or cant change an impeller I recommend that you pay someone who can.

As I say ...Just cos you seen it on YouTube don't mean its right or you can do it.

[fruitspice]

The problem is as a qualified mechanic we are asked what the fault is by a layman {no offence intended} and often the description of the fault from the layman is incorrect and that is why you will see 10 different posts from 10 different people of what the fault is.I would not be mucking around with a outboard engine if you cant do or do not understand the basics in mechanics or electrical.If you don't know how to pack bearings,use a multi meter or cant change an impeller I recommend that you pay someone who can.

As I say ...Just cos you seen it on YouTube don't mean its right or you can do it.

Yep that's what I've done mate was never going to try to fix myself just wanted some advise so I'd have an idea of causes of this and what it might be in a previous post I've said that the mercury service centre have they are 99.99% sure it's the cdi box and am having it replaced at a full cost of $580

Thanks for your comment !! I totally agree with you

[fruitspice]

Things all fixed was the cdi box running like a dream now !!! Thanks everyone for your advice