merc 80hp acceleration problem

I

iaincwil

Seaman Apprentice
Joined
Jun 21, 2006
Messages
33
we have sorted out the tell tale flowing well now, BUT now we have a problem with the acceleration when we put it in gear (fwd or rev) it will just run but as soon as we try to open it up the thing dies in the water!! unless we hit the choke button then it takes off like a bat out of hell but you have to keep hitting the choke or it starts to slow off and quits,

its a bit dangerous with such a powerfull motor so anyone any ideas, could it be the fuel pump ?? if indeed it has one
 
C

crunch

Commander
Joined
Aug 1, 2006
Messages
2,844
Re: merc 80hp acceleration problem

Hmmm,

Looks like the experts aren't going to pitch in...

unless we hit the choke button then it takes off like a bat out of hell but you have to keep hitting the choke or it starts to slow off and quits

Obviously lean... plugged fuel filter? restriction in fuel line? fuel pump weak? carbs full of crud? etc...

What is the serial #?
 
I

iaincwil

Seaman Apprentice
Joined
Jun 21, 2006
Messages
33
Re: merc 80hp acceleration problem

Hi! its a blueband with thunderbolt ignition 80 hp dont have the serial no without going out on the water and getting it if its fine will probably go tomorrow but its blowing a gale and rain to boot,
will check out the things you have mentioned then have looked for fuel pump but couldnt find it but it has to be between the connection and the carbs,
I have noticed that where the p/pipe connects to the engine the fixing has a plastic cover which is bolted on and when you squeeze the bulb it squirts out of there could it be sucking in air??:%
 
M

mckeemm

Petty Officer 3rd Class
Joined
May 17, 2006
Messages
98
Re: merc 80hp acceleration problem

iaincwil said:
Hi! its a blueband with thunderbolt ignition 80 hp dont have the serial no without going out on the water and getting it if its fine will probably go tomorrow but its blowing a gale and rain to boot,
will check out the things you have mentioned then have looked for fuel pump but couldnt find it but it has to be between the connection and the carbs,
I have noticed that where the p/pipe connects to the engine the fixing has a plastic cover which is bolted on and when you squeeze the bulb it squirts out of there could it be sucking in air??:%
Click to expand...

Hi, No expert here but i'm slowly sorting out some similar problems.

On my 70 hp 3cyl the telltale line comes off the fuel pump housing. The pump, I assume is water cooled to prevent overheating under the cowl and some sort of vapour lock problems.

If you pump your fuel bulb and get fuel leakage arond the pump housing then you may well be sucking air at WOT.

I suggest a pump rebuild or replacement.

Mark
 
C

Chris1956

Supreme Mariner
Joined
Mar 25, 2004
Messages
27,158
Re: merc 80hp acceleration problem

Ian, That motor has a vacuum powered fuel pump, driven by the crankcase pulsations.

If you need choke to get on plane one or more of your carbs are set too lean. Open the top one 1/8 turn and try to accelerate. If no good, open the next one 1/8 turn and try to accelerate. Repeat sequence until acceleration is smooth. In general, motor should idle reasonably well, but accelerate well!
 
Texasmark

Texasmark

Supreme Mariner
Joined
Dec 20, 2005
Messages
14,559
Re: merc 80hp acceleration problem

As I recall the fuel pump is right in the side of the engine block, on the starboard side, in the center. Has a fuel line in and one out. If you follow the fuel line from the engine's input you have to come across it.

Too lean a carb can and will cause this problem too and it can be cured with as little as 1/8 to 1/4 turn open.

Also, and here we go again, do a decarb with Sea Foam. BTDT

Mark
 
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