1999 Mercury 4 stroke 40hp low power and stalling

[djbdjb]

I'm re-posting in hopes that someone can help.<br /><br />I bought this boat (16' Key Largo) used, it had been sitting for about 6 months. The motor starts and idles fine, but stalls and/or bogs down when the throttle is opened. It also stalls when moving from full throttle to idle speed. It doesn't want to run well in mid throttle range and has problem getting on plane. I emptied the fuel tank and put fresh gas in, no better. I took it to a Mercury dealer, they put it on the computer, but found no problems. They vacuumed and synched the carbs. When I got it back, it was 50% better, but it still stalls when throttle is pulled back and has no power in mid rpm range. Once it reaches top speed it runs well, it's just difficult to get it there.

 

[ronnieboy]

Re: 1999 Mercury 4 stroke 40hp low power and stalling

my 2000 30 hp did the same thing, had to remove caps on carb adjustment and enrichen all 3 carbs. merc mechanic said he couldnt do it cause of polution restrictions, drill out cover cap and back out screws 1/4 turn and try it. hope this helps , ron

 

[ronnieboy]

Re: 1999 Mercury 4 stroke 40hp low power and stalling

by the way, what size and pitch prop are you running on your motor? mine is a 10 1/4 x 14 pitch.

 

[djbdjb]

Re: 1999 Mercury 4 stroke 40hp low power and stalling

Thanks for the reply, I'll look into the carb adjustment. I'm running an SS 10 3/8 x 13.

 

[djbdjb]

Re: 1999 Mercury 4 stroke 40hp low power and stalling

I don't see the caps to drill out, where are they located ?

 

[ronnieboy]

Re: 1999 Mercury 4 stroke 40hp low power and stalling

look on carb body, they are bout 3/8 of an inch, and brass , be carefull not to drill to deep, will screwup a lot of stuff , if to deep. adjust very little, good luck ron

 

[ronnieboy]

Re: 1999 Mercury 4 stroke 40hp low power and stalling

the plugs are very thin and 1/16 deep should do it.

 

[djbdjb]

Re: 1999 Mercury 4 stroke 40hp low power and stalling

I just realized I never put any closure to this thread (3 years later).
After many return trips to the mechanic the problem was clogged jets in the carbs and prop that was not sized for the boat correctly.