boat acceleration

[ubdkdd]

hey,

I am relatively new to boats, but am having some probs with my outboard.

I have a 90 hp mercury oil injected outboard which is causing me all kinds of headaches. I had the carbs stripped and cleaned earlier in the year, and a general service, at which point we bypassed the oil injection and started using premix... once done, it worked perfectly.

Now, however, when ever i open the throttle, the boat gets to about 60% of its previous revs and power, then just sits there. Occassionally, after a while of sitting one the plane at that output, it will find the remaining 40%, and taken off at a great rate, nearly leaving me in the water behind. It also seems to be sucking more fuel that it previously did.

I have checked everything i can think of as to what would be casuing it. I am presently thinking that maybe i ran a tank/s with a too heavy fuel ratio and things have got clogged up again... but, am not sure.

Any suggestions on why it might be happening??

cheers.

[peterbo3]

How old is the fuel? Premix tends to degrade quicker than straight unleaded. If the fuel is fresh, then I would start with the carbies again. If you are using E10, that too may be a factor.

[dreemon]

sort of sounds like a fuel prob and starving , but using more fuel shows it getting enough, maybe to much if a float is stuck open, a de-carb might help too ? does it smoke more ?

[Monza]

Could be a spark problem. Does the motor sound a bit coarse/rough when running at full speed. It may pay to change the plugs.

I had a motor that ran fine at lower revs, but ran out of puff above 3500rpm. Turned out to be a faulty spark plug (which was fairly new) which stopped firing at higher revs.

[boatboy50]

Hey,

Buy some $5 spark plugs and try that 1st. That'll be my bet, and it's more than likely because they are oiling up with a higher ratio being used now to what the engine was designed.

It never amazes me the amount of mechanics who recommend removing injection, even though the rate of failure is very very low in modern engines. Make sure your alarms are working, and keep the injection as it was designed.

Regards

Darren.

P.S. I used to own one of those engines for many years, so I know them very well.

[ubdkdd]

fuel is brand new, with valvoline outboard oil, and yep, it has been smoking a lot more.

I took it out this afternoon, and put through a few litres of fuel with less oil than the normal ratio. It ran at the 60% as it had been doing. But then, when i changed back to a tank with the normal fuel ratio, it found full power and ran perfectly.....

[Steeler]

Hi ubdkdd

Check the obvious things as previously mentioned but i would also suggest a compression test,maybe showing first signs of a bottom powerhead seal on the way out and creating firing issues on the bottom cylinder.Not at all uncommon on these things.I have a 3 cyl 90HP 93 model.

Cheers

Steve

PS : the oil injection system on these is quite reliable,more often than not as mentioned by boatboy its a delaminated magnet in the bottle or faulty buzzer that sends the alarm system off on these motors.The best way to ensure the system is working is monitor your oil usage from the bottle and every 6 months or so perform a oil output test where the oil and fuel come together at the fuel pump.These things are very lean at idle and richen up at speed,by doing away with the injection system you are 50:1 all the time hence the smoking.

[Spaniard_King]

Hey,

Buy some $5 spark plugs and try that 1st. That'll be my bet, and it's more than likely because they are oiling up with a higher ratio being used now to what the engine was designed.
.

Darren would you mind to PM me with the location I can buy the $5.00 merc plugs BUHW-2's as I need to stock up on them

[boatboy50]

Darren would you mind to PM me with the location I can buy the $5.00 merc plugs BUHW-2's as I need to stock up on them

Hey Gary,

I sold that engine back in about 2000, so inflation has probably played havoc with the price of the plugs!

Regards

Darren

[Spaniard_King]

Like all things boating Darren, they are overpriced.. RRP around $11.00 a plug.

[supa29]

hey mate are you using e10 or normal unleaded if so check out my thread and pm me for the sheet sounds like my problem to a tee fixed it by using premium fuel now goes like a dream.

supa