99' mercury 30hp 4 stroke problems

[Dbishop3]

I have a 99 merc four stroke serial numb. Og907201. It starts with the touch of the button idles great goes in gear great. The problems start when i get to 3/4-full throttle it wants to bog down and die. Dosent cough or sputter kinda growls. I can run at 1/2-2/3 all day long with no problem until i throttle up. Now, when i am ready to stop when i throttle back it also wants to die. I can shift it to nuetral when this happens and it stays running. Or if i throttle back very slowly i can keep it running. When this happens the primer bulb is firm and pumping it has no affect. Ive replaced fuel lines, tried merc quick clean/seafoam and stabil every fill up. Only thing i havent done is tore the carbs apart and gave a good cleaning. The lync n sync process is keeping me from doing this. I have rebuilt carbs and am halfway mechanically inclined. I did drain the bowls and sprayed different carb cleaners in and let it soak. Any help or ideas to get me headed in the right direction would be greatly appreciated. If you need any more info let me know.

 

[CharlieB]

Re: 99' mercury 30hp 4 stroke problems

Limited power can be caused by either a restricted fuel supply or a weakening ignition. Both must be tested to determine which system needs attention.

Depending upon the enrichment system your carbs uses you may 'bump' the enrichener/choke as the condition occurs to see if the additional fuel improves power, if so, carb cleaning may be in order.

An inductive tach or timing light may be used to see if the ignition is failing as the condition occurs. Check each plug wire as power falls off to see if spark is lost on any cyl.

 

[Dbishop3]

Re: 99' mercury 30hp 4 stroke problems

How would i go about bumping the choke? It has the auto/elec. Enrichner. Also the id tag under cowl says "timing not adjustable." one more question is it possible to tear into the carbs without doin a link n sync afterwords? As i said any help is appreciated.

 

[Silvertip]

Re: 99' mercury 30hp 4 stroke problems

A weak fuel pump can also cause fuel starvation at higher throttle settings. When the problem occurs, have someone squeeze the primer bulb several times. If the engine picks up, the fuel pump is suspect. A restriction in the fuel delivery system (from the dip tube in the fuel tank to the engine) can cause the problem as well. If you are using a portable tank, empty it while straining the fuel. If you find bits of red plastic, those bits may be plugging the screen on the bottom of the dip tube. I've seen this many times. Out of curiosity I check a couple of these new tanks whenever I pass them in a store. About 20% of the time I see many bits of plastic in the bottom. The bits are drilliings from the manufacturing process. I had this problem some years ago on one of my own tanks. If the pump and lines are not the issue then carb rebuilding is required.

 

[Faztbullet]

Re: 99' mercury 30hp 4 stroke problems

Has the engine been setting or in storage ? Did this just suddenly happen or as it been a ongoing issue? Have you been using a ethanol fuel?

 

[Dbishop3]

Re: 99' mercury 30hp 4 stroke problems

The motor is used year round. It has been an on going prob. Since i bought it. The longest it sits is probably a month. It hasnt been in storage. The guy i bought it from showed me a receipt of the carbs being rebuilt. I didnt think about it at the time. But why would you get the carbs cleaned if you werent having problems. I can pump the bulb with no affect and it is firm when the problems happen. I do use ethanol fuel?

 

[CharlieB]

Re: 99' mercury 30hp 4 stroke problems

It is possible to have a restricted fuel hose after the primer. Even one carb having a limited fuel supply will reduce power, cause problems, and when it goes very lean, will melt the piston.

Test fuel supply to the carb(s), one at a time, disconnect the hose to a carb and direct it into a suitable container, also pull the lanyard to kill the ignition, you do not need to start the motor.

Crank the motor and watch the fuel stream, it should be a strong pulsed flow. Repeat test on each carb fuel hose.

Disconnect the fuel hose immediately after the primer bulb, point it into a suitable container and squeeze it, note the volume and the ease of the fuel flow. Squeeze the primer whille each carb fuel hose is disconnected, does each carb fuel hose pass gas near the same volume and speed at it did when disconnected at the primer?

Once fuel supply to each carb is confirmed you can move onto testing the high speed ignition.

 

[Dbishop3]

Re: 99' mercury 30hp 4 stroke problems

Thanks for the input. I will try these fuel flow test when i Get home from work today and get back to ya. As i said i appreciate the help.

 

[Dbishop3]

Re: 99' mercury 30hp 4 stroke problems

All the carbs seem to be getting fuel just fine. On to the ignition.

 

[CharlieB]

Re: 99' mercury 30hp 4 stroke problems

Go here to download a copy of the service manual

http://forums.iboats.com/showthread....11#post2072211 Don't bother, dead links.

Select the 30-40 in the 4 Stroke listing, hit the download button and wait for it, save it to your computer.

Remember the password 'ribforum' you will need it to decompress the file

Once downloaded, run a decompression utility like WinZip, WinRAR, or another to decompress the file.

Study the ignition section 2a

 

[Asurf]

I was not able to open link.