40 HP Mercury stalls when given trottle

[John P]

I have a 40 Hp outboard that runs fine when I put a garden hose to it and run it in the driveway, but when I drop the boat in the water it will do one of two things - it will idle fine and run at half of what the engine is capable of or it will idle weakly and die when I give it some trottle. This situation has been extremely frustrating because as soon as I take it home and stick a water hose to it and run it in the driveway it runs fine. <br />Thanks for any suggestions given,<br />John P

 

[12Footer]

Re: 40 HP Mercury stalls when given trottle

Welcome to iboats, John.<br />It will be a process of elimination.<br />1.Check the fuel filters, hose connections,tank venting,and tank contents.If the fuel is over 6 months old, clean the tanks out,and start with fresh fuel. <br /><br />2.Check the engine's compression. Low compression will fail to operate the fuel pump, and also not allow for exaust gasses to escape.<br />3.Decarb the engine,using a good spray decarb cleaner and recheck the compressiion.This will also help if the exaust ports are plugged, in many cases.<br />4.Squeeze the primer bulb when the symptom occurs, and see if the performance improves.If it does, Rebuild the fuel pump and clean the carb.

 

[lightbuilder]

Re: 40 HP Mercury stalls when given trottle

Have you tried adjusting the air fuel mixture screw on the carb, count how many turns inward until it gently seats then back it out 1 1/2 turns. To fine tune the adjustment boat must be in the water in forward gear. Good luck

 

[Dunlop]

Re: 40 HP Mercury stalls when given trottle

John before you waste any of your time and money on the Merc, give it the simple ether test. Have the engine running in the driveway, and just spray ether where the case halves join and under the flywheel. If the engine stalls, its sucking air,through the crank seal or the halves. Chances are its not worth bothering to try to fix it if its an older motor. Let us know what you find.

 

[John P]

Re: 40 HP Mercury stalls when given trottle

Thanks for the response 12Footer, Lightbuilder, and Scotty221. Appreciate it very much. The motor was bought brand new in '94 and hasn't been used much. I plan to work on it this weekend and will keep you guys updated.