1999 Mercury 40 4 Stroke - Dies on Rapid Acceleration

[PTocko]

I bought this boat last year (used from a dealer) - and really since day one if I really hammmer it from idle it will hit about 3000 RPMS and die. If I back off quickly I can keep it from dying. Now if I accellerate slowly it will rev up with no problem. The problem area seems to be about 3000 rpms - per the tach. I brought the boat back into dealer last summer (they gave me 45 days) with a list of things that needed to be done and they said they looked at the motor and everything is okay. Problem continued for the rest of the year. When I put it away last fall I cleaned the carbs, changed the fuel filter, Changed Engine Oil and Lower Unit. This spring I added a water fuel separator and a new primer bulb. Took it out last night - same problem. Other than this "glitch" the motor runs well. Starts easy, idles well, get past the hiccup on accelleration and it runs on the top well too. Because this only happens when I hammer it - it is really more of an annoyance than something I am really worried about. In reading the repair manual it seems like my carbs may need to be sync'ed - I guess I would assume the dealer would have looked at this when I brought it is. Any other ideas on what this could be would be appreciated. As I said - other than this problem I have been happy with the overall performance. Thanks for any help. Paul

[marine_man]

Paul - any idea if the dealer water tested the boat? It sounds like it's pretty easy to repeat the problem...

marine_man

[boatfixer]

The accelerator pumps in the carbs are very sensitive. I've seen them leak back up through the accuater shaft. Usually if they are bad it will die as soon as you hammer it though.

[PTocko]

Thanks for the quick responses -

MM - They said they did water test it. Don't have any reason to doubt them. Obviously not sure what was involved with their water test. I agree, I was suprised they could not get it to repeat as it happens to me almost everytime, unless I accellerate reletively slowly, then it is okay. Only when I give it a quick twist (zero to WO all at once) from idle does it happen.

Boatfixer - I have not heard of accerator pumps before - is this something easy to replace / look at. Is it something you replace, rebuild or is it terminal. I will look in my service manual to see any reference to this - I do not recall seeing anything but it sounds like it could be it.

Again, thanks for the help, I do appreciate it.

[PTocko]

Update - I looked in the manual that I have (Clymer 4-90 HP 4 Stroke 1995-2000) and the 50's on up have accelerator pumps, everything below does not. Maybe I missing something. Again, thanks for the help. Paul

[marine_man]

Have you tried hitting the choke to see if it picks up when you accelerate?

marine_man

[PTocko]

MM - yes, I have tried depressing the choke as it happens (it happens kind of suddenly) - no effect. It is really bothersome because otherwise everything works great. I believe I have adressed everything regarding fuel delivery with the exception of sync'ing the carbs which I am going to attempt this weekend.

Another note on the accelerator pumps - I did find an additional reference in the manual. It seems that the pumps on the 40 hp are integrated into the carbs. They look like a small screw but there is little information about adjustment / repair / maintenence so I am not sure what if anything can be done about the accellerator pump.

Thanks for the help guys - I do appreciate it. Paul

[marine_man]

I'd work through the synching process and see if that does it.

marine_man