1983 Mercury 90HP outboard (3carbs) Bogs out when hot

[Mdchev]

I believe i may need a carb adjustment. The boat runs fine for a while, but after maybe an hour as soon as I throttle up the motor bogs until i put it in neutral...any ideas?

 

[racerone]

Open low speed mixture needles 1/8th turn and test.----Repeat as needed.

 

[BrianVT]

Performance issues when hot is sometimes from the coils going bad.

 

[jimmbo]

Welcome to iboats

When it does the Bog, how long after starting did it run before you gave it throttle?

 

[Mdchev]

Welcome to iboats

When it does the Bog, how long after starting did it run before you gave it throttle?

About 5 minutes

 

[Mdchev]

Open low speed mixture needles 1/8th turn and test.----Repeat as needed.

Oh boy...which one is low speed on the carbs?

 

[jimmbo]

Get the Correct, Factory Service Manual for your engine, before you touch anything

 

[BrianVT]

If it was running good before then I wouldn't mess with the jets.
I only mess with jetting when dealing with major changes in altitude or air temperature.
If the problem seems to be engine temperature then I'd suspect the cooling system or the coils or compression.
Is the impeller peeing water normally? Have you checked the compression on the cylinders?

 

[racerone]

Some will argue.-----Opening low speed mixture needles often cures bogging.-----Costs no beer tokens to test.

 

[BrianVT]

About 5 minutes

Wait. I thought you said it was fine for about an hour?
If it always bogs when you try to throttle up then we've got a whole different approach.

 

[BrianVT]

Some will argue.-----Opening low speed mixture needles often cures bogging.-----Costs no beer tokens to test.

True. Going richer shouldn't hurt anything except a bit more smoke and maybe fouled plugs. But I don't think we have enough info. from this person yet to send him into doing something that he's not even familiar/confortable with.

 

[Mdchev]

Ok...got the boat out today. I noticed when it starts bogging, I put it in neutral an then it revs high and normal. Soon as I put it into gear is when it starts doing that.

 

[BrianVT]

It does this from the start? Or after 5 minutes? Or after an hour? You haven't cleared that up yet.

Is something wrapped around your prop. shaft?
Fouled spark plug(s)?
Low compression?
Fuel restriction? (crap in filter or quick connector or carbs)
Exhaust restriction? (carbon buildup)
Coil(s) going bad?

 

[Mdchev]

It does this from the start? Or after 5 minutes? Or after an hour? You haven't cleared that up yet.

Is something wrapped around your prop. shaft?
Fouled spark plug(s)?
Low compression?
Fuel restriction? (crap in filter or quick connector or carbs)
Exhaust restriction? (carbon buildup)
Coil(s) going bad?

It does it after about ten minutes.

 

[BrianVT]

I asked before but you didn't answer.
Is the impeller peeing water normally?

 

[Mdchev]

I asked before but you didn't answer.
Is the impeller peeing water normally?

Yes...its normal

 

[racerone]

Tried opening low speed mixture screws, yes or no ?----Or perhaps you think that can't be the problem here ??

 

[BrianVT]

Yes...its normal

And my other questions?

Is something wrapped around your prop. shaft?
Fouled spark plug(s)?
Low compression?
Fuel restriction? (crap in filter or quick connector or carbs)
Exhaust restriction? (carbon buildup)
Coil(s) going bad?

 

[stresspoint]

unless you have made changes to the motor there should be no reason to mess with screws or settings .
i would say you have gummed up plugs or a internal carbon problem ,
im not sure if you can still buy it , but you used to be able to get some snake oil in a can that breaks down carboned up 2 smokes .

 

[BrianVT]

i would say you have gummed up plugs or a internal carbon problem ,

Lots of low-rpm running and/or excess oil mixed into the fuel can cause this.
Also an obstructed air intake would cause a rich mixture. There's another thread here where a mud dauber built his home in an air intake.