Logo
FULL SITE MENU

90Hp Mercury late 80's early 90 model

L

leontaylor

New member
Hi guys,
I have two of these motors that really struggle to go in the water. I bought the boat with motors not installed. Fitted the motors and all electrical is working fine.
On land they idle and ref perfectly but in the water they struggle. The boat get on plain (max 28Km/h) with both motors on full throttle but that's it.
I have done almost everything, Carbs redone, checked the reed valves, new kit in fuel pumps, spark plugs and spark, compression test (one motor 120psi the other motor 115psi) , checked the exhaust for blockage, fuel lines and filters, adjusted the air/fuel mixture etch.
What is concerning s that both motors are doing the same. I even adjusted the Hight of the motors and play with the trim and tilt with no real difference. No water in the hull.
Both motors are fitted wit 18" s/steel props?
When running in the water its like running through mud.
Anny suggestions and help will be appreciated.
Thanks
 
Common fuel tank? When you increase throttle, do the engines increase in rpm smoothly? What Too much/little pitch on props?
 
No each motor with a fuel tank. The engines do increase in rpm but not to where it suppose to. did check the throttle setting and the carbs do open all the way. I forgot to mention that they are extremely heavy on fuel. the one motor use almost double the amount of the other one but both perform poor in the water. Clearly not enough refs on full throttle.
Can the crank seals or power head/exhaust gastet contribute to this?
 
With that much power, that rig should be a rocket!

You have major carb problems/ and or leaking fuel pump diaphragms. My money is on the carbs.

Jeff
 
Hi,

I think you are overpropped, i had twin 75 mariners with 17 pitch props and same size boat (albeit a cat hull) and was getting 58 km/h at 4500 rpms.
Fuel consumption was very bad on these two strokes.
 
Something is wrong here.------An 18' boat with 2 Mercury 90 HP motors should go 70 km/hr or more.-----Run to a boat shop to get it checked out.----Any pictures of this boat and motor set-up.-----20" transom with 20" motors ?
 
Thanks for all the inputs thus far, I will double check everything mentioned and report back
 

Attachments

  • IMG-20190502-WA0002.jpg
    IMG-20190502-WA0002.jpg
    58.7 KB · Views: 28
What rpms are the outboards running,when you at wot?
if you getting to 5000 or more then it might be a spun hub on the props.
18 inch pitch on the props and that mono you should be running easy past 60 km/h or more.
 
Even in gear on the trailer is still neutral.------The props do no WORK.------Your testing on the trailer means nothing.------Find out what the real problem is.--------Maybe the motors are mounted too close together.-----Hurry and run to a good boat shop here.-------Sounds like one motor is not contributing power.------Maybe some ignition wires are not on the correct terminals !!
 
Back
Top