Mercury 4 stroke 90 - kills under load?

[oaklake]

Hi, Please Help! -- I've got a 2002, (I think), Merc 90 4 stroke on my 24' Benninton pontoon. Starts ok out of water, starts ok in water and even revs up in nuetral but as soon as its shifted in gear or put under any load it kills. The idle is also spuratic, even when I try to keep at say 2000 rpm in nuetral it wants to rev up and down by itself sometimes. This problem has been getting worse over time to the point where I can't even move the boat. I tried to look for something simple like spark plugs but I cant even see them (too much electronic gobblygook packed in there). Fuel was drained last fall and replaced with fresh this spring?

Any ideas?

 

[Jugfisher]

Re: Mercury 4 stroke 90 - kills under load?

Coulb be any number of problems. Just somthing simple to rule out anything major try doing a compression check. Make sure all cylinders are operating properly. ALL of them should be giving a reading that is very close to the other, I think about 115# per valve. Give are take a few. Be sure your batteries are good and charged and your compression checker works properly.

It is a good starting point, but as I said it could be a number of things. Just need to start with process of elimination.

If compression is good. Try priming the bulb while accelerating. If that helps. You may need to look at your fuel pump or fuel lines.

How long since carbs have been cleaned?

 

[oaklake]

Re: Mercury 4 stroke 90 - kills under load?

Thanks, last time I looked under the cowling I could not even see where the plugs would be?? Are there any good digrams on line??

I have not cleaned the carbs, I'm not even sure what year it is?

I found a registration that shows 0T039940 (serial) and 1-00520ZK (model) any idea where I could look up the specs / year built??

 

[Jugfisher]

Re: Mercury 4 stroke 90 - kills under load?

Personally I do not know. I would buy a manual for your motor to help walk you through the procedures. It will help in locating equipment also. You can get one here on Iboats. It is worth it. I am not a master mechanic like alot of these guys on here. I have a similar problem which they have been helping me with. I am just giving advice that I have been given.

 

[oaklake]

Re: Mercury 4 stroke 90 - kills under load?

Sure, thanks. I've been looking online to try and figure out what year it is so I could buy the right manual, but I have hade no luck.

If anyone knows how I could cross ref. the model/serial #'s to figure out the year that would be great!

Thanks!

 

[oaklake]

Re: Mercury 4 stroke 90 - kills under load? (FIXED!)

Re: Mercury 4 stroke 90 - kills under load? (FIXED!)

Just a folow up. I bought a compression tester, Seafoam and plugs to start. Worked on it while in the water. First thing I tried was replacing the plugs, it fired up, and now runs great! I then added the seafoam to the tank anyways. I can't believe it was so simple. I am glad I found this site. I will return the unused tester. I'm so happy I did not have to tackle the carbs or anthing else!