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90hp mercury outboard bogs under load

acarte16

New member
90 hp mercury.
Bought my boat last summer ran great, put sta-bil in the gas for the first time. After running the engine for about an hour, it begain to bog. We managed to idled back to the ramp and took it home. Replaced gas in hopes it would run ok, but again the same problem. In the driveway with the muffs, runs fine, rev's fine but when put in water and under load it bogs. I have sprayed carb cleaner in carbs and put sea foam in the fuel...still having the same problem HELP........
 
Probably your fuel. Forget carb cleaner & Seafoam. That kind of stuff is pretty much useless.

First steps.

Take a sample of your fuel (from the tank.) You'll want to disconnect the fuel line from the engine and use the primer bulb to pump some fuel into a glass jar, or some other kind of other clear container where you can see the fuel. Pump in a good amount of fuel (a good cup or two worth.) Your fuel should look nice, crisp, and clean with little to no debris in it. If it's cloudy, then theirs water in it, and it will settle to the bottom of the container. Water in your fuel is bad, and this will cause your bogging problems. You will definitely notice it in the container if there is a significant amount of water in your fuel.

If you find this, you will have to clean your carburetors. Forget using carb cleaner. That stuff is junk, and actually eats away at the surface of the carburetors over time. If you want to do the work yourself, reply back, and I'll guide you through it. But, if you're not comfortable with it, I'd bring it to a professional.

Along with cleaning your carbs, you'll also have to get rid of all the fuel in your tank. Hopefully, you don't have that much in there. But engines definitely don't run on water and debris, so it's necessary.

I also can't emphasize enough how important it is to take care of the fuel in your boat. The ethanol in gasoline has been nothing but an absolute nightmare to boaters since it became an additive 10 or so years ago. Good fuel turns to bad fuel in a matter of weeks if you don't take care of it. You must realize that ethanol attracts and absorbs 100% of it's weight in water. Best thing to do is to always stabilize your fuel, always make sure all your fuel caps & vents are working the way they should, and run your boat often. The more that stuff sits around in the tank, the harder it is to keep in good condition.
 
My 90 hp optimax runs fine up to 3500 rpm when I take it up to 4000 + it stalls out unless I drop it back to neutral. How can I check for fuel starvation ?
 
Would direct injection have idle screws?

No. You need air/fuel gauges to check the pressures in the air and fuel rails. Opti's have several fuel/air pressure regulators and a "tracker valve" which all can cause the RPM loss you're experiencing.
 
Can a low oil warning cause the engine to derate?
you may want to check the inside of fuel line for deterioration. mine was doing the same and it was the fuel line melting from the ethanol content in the fuel and blocking fuel flow to engine. this hoses i bought from mercury don't last and melt internally. replace two sets within six months!
 
you may want to check the inside of fuel line for deterioration. mine was doing the same and it was the fuel line melting from the ethanol content in the fuel and blocking fuel flow to engine. this hoses i bought from mercury don't last and melt internally. replace two sets within six months!

Im having a similar problem but starts no problem, idles nice, revs round to 5200rpm and maintains that without missing a beat but getting the boat onto the plan (1800-2200 Rpm) the engine bogs to the point that if you try to get away fast it stalls / cuts out so you have to creep onto the plan and it's perfect after that.
The carbs have been stripped, sonic cleaned and rebuilt, new fuel but the problem is the same.
the boat is a 5.8m Humber assault rigid inflatable so not heavy.

any ideas what to try next ??
 
Im having a similar problem but starts no problem, idles nice, revs round to 5200rpm and maintains that without missing a beat but getting the boat onto the plan (1800-2200 Rpm) the engine bogs to the point that if you try to get away fast it stalls / cuts out so you have to creep onto the plan and it's perfect after that.
The carbs have been stripped, sonic cleaned and rebuilt, new fuel but the problem is the same.
the boat is a 5.8m Humber assault rigid inflatable so not heavy.

any ideas what to try next ??
please ??
 
Hi I have a optimax 90hp 2006 and I can’t get it passed 4400 rpm I have check and change the prop I have the same prob as a lad who has the same boat and outboard and he is getting 5700 rpm any ideas on this thanks
 
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