30 HP 1999 4-stroke Merc Trouble Accelerating

dbuckland

Recruit
Joined
Aug 28, 2003
Messages
5
I'm a newbie and love this forum!!<br /><br />I have a 30HP Merc outboard 1999 4-stroke, sn:OG907873, mod: 1-F30312VD. It is hesitating during acceleration and occasionally stalls if I try to push the throttle to get it over the "hump" to where it will continue to run.<br />As a mechanical engineer I just had to try to diagnose the problem myself and here is what I learned. I suspect the accelerator pump.<br />I took off the air intake manifold and watched as I accelerated. The bottom two carbs are shooting fuel into the butterfly but the top jet is not "tipping in" the fuel. The accelerator pump plunger and bellows on the top carb travels fastest to its end-stop which makes me think that the plunger is the culprit. Also, when I take off the top plate and rubber diaphragm and spray into the holes, the jet discharges the spray?? Any thoughts?
 

dilligafda

Petty Officer 1st Class
Joined
May 13, 2003
Messages
315
Re: 30 HP 1999 4-stroke Merc Trouble Accelerating

OK, I have a few thoughts I would bne willing to share with you and anyone else that is willing to listen :) I don't think there is anything wrong with your accellerator pump. More likely there is a problem with the carburators. The accellerator pump does not actually spray fuel, it uses air to pressurize the fuel bowl and forces fuel through the main nozzel into the intake. If there is blockage in the main nozzel or the air lines to the carbs, fuel does not get into the engine fast enough and the engine stalls. A quick trick to clean this type of debris from the carbs is to remove the drain screws and fill the float bowls with Mercury PowerTune or similar product and let it soak for about 15-20 minutes and run the engine. If that doesn't take care of the problem then you will probably have to take the carbs off and clean them the old fashioned way. Hope this helps!
 

The Marine Doctor

Commander
Joined
Jul 25, 2003
Messages
2,177
Re: 30 HP 1999 4-stroke Merc Trouble Accelerating

When the engine was originally purchased did the dealership put AntiTamper on the screws that are used to syncronize the carbs?<br /><br />The carbs must be set up with a vaccuum guage. If they come out of sync...you will stumble and have poor idle.<br /><br />TMD
 

dbuckland

Recruit
Joined
Aug 28, 2003
Messages
5
Re: 30 HP 1999 4-stroke Merc Trouble Accelerating

Thanks for the input!! I'll try your suggestions this weekend and see if it helps. As I'm in a remote water access island it sure would save me a bunch of $$ if I can save myself a trip to the mechanic.<br /><br />Cheers eh!
 

dbuckland

Recruit
Joined
Aug 28, 2003
Messages
5
Re: 30 HP 1999 4-stroke Merc Trouble Accelerating

Alright, I stuffed the 3 carbs full of "Power Tune" and also changed the plugs, let it sit then ran it clean. Seems to have helped quite a bit. There is still some hesitation on acceleration so I'll give it one more cleaning when I'm up next. However, after running at full power for about 10 minutes, I will gradually lose power. Sometimes it comes back on its own in about a minute but other times I have to reach back and pump the bulb which is soft at this point. Am I losing primer pressure? Filters look clear, gas is new, what else could be causing this?<br />Hope everyone had a happy labour day!<br /><br />MooseDeer
 
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