no power on merc 115

[grpratt]

I have a 1985 Mercury 115 HP - brown band I think - which at the moment starts okay, idles well, but as soon as I apply power, it won't get above 3000 rpm, and surges between 2800 to 3000 rpm. I've checked fuel, fuelines, plugs with no luck.<br />Any suggestions?

 

[Bear]

Re: no power on merc 115

If you pump the primer bulb a few times and it picks up it is time for a fuel pump kit. I think you got a small hole in the diaphram.<br /><br /> http://marinemechanic.com/2000/images/ob_fuelpump.htm

 

[grpratt]

Re: no power on merc 115

Thanks Bear<br /><br />I have tried pumping the primer bulb but it has no effect or change at all!

 

[Bear]

Re: no power on merc 115

Okay. We don't know that much about your engine so let's start with a few questions:<br />Did you just buy it, did it just happen, was it stored for a long period of time?<br /><br />I'm thinking gummed up carbs (high speed jet/s), dirt and or water in the carbs and fuel filter. Drain your float bowls in a clear and dry container, like a glass bottle. <br /><br />Do you have a spark at all plugs. How do they look, black or tan, wet, or like new and steam cleaned? Do they all look the same?<br /><br />What can you say about the primer bulb when this happen at 3000 rpm? Soft, all compressed or firm? Is it possible that you have vacu*m in the fuel tank?<br /><br />Do you have a manual?<br /><br />Let us know a little more

 

[bossee]

Re: no power on merc 115

Hi,<br /><br />Are you sure the outboard is running on all cylinders?<br />Is the fueltank ventilation opened? Do you use an internal or external fueltank? For a test try external fueltank if you have an internal tank.

 

[grpratt]

Re: no power on merc 115

Bear and Bo - thanks for your reply.<br /><br />I have had the boat 8 years with no problems - a regular yearly service at my local centre seems to have looked after it okay. It has been laid up for almost a year, but with regular starting. <br /><br />I have travelled 1500km up the east coast with the boat for the xmas holidays! Checking the plugs a short time ago shows me a variety of conditions - from a couple looking perfectly clean to another couple bit oily looking. I don't know what that means!<br /><br />Thanks again

 

[Bear]

Re: no power on merc 115

(115 Hp serial number 6630171 - A907776 1985 6 cyl inline )<br /><br />Oily plugs means weak or no spark in this case I think.<br />Clean them good and move them to the cylinders where the clean plugs where. Try again. If the same cylinders gives you oily plugs again I'd check the high tension cables and spark plug booths. Look for corrosion. Then I check or switch the coils. Or give the local mechanic a call.<br /><br />I don't know which parts you can move around. But if you do that and the problem moves too, you are on the right track.<br /><br />When was the last time you replaced all spark plugs?

 

[tbjtib]

Re: no power on merc 115

Hi, my 90 merc did the same,turned out to be a bad switchbox.Try moving the boxes (top one to bottom,bottom to top)and see if it makes a differance.

 

[bossee]

Re: no power on merc 115

>...to another couple bit oily looking<br /><br />Depending how to interpret "bit oily" it seems that one or more cylinders have not good enough temperature for the self cleaning process of spark plugs to work.<br />Have a look at this picture:<br /><br /> http://www.ngksparkplugs.com/techinfo/spark_plugs/overviewp3.asp <br /><br />Do You get a spark on suspect cylinder(s)?<br /><br />Maybe try a compression test on all cylinders if possible and then you can compare compression readings on cylinders with "normal" spark plugs and cylinder(s) with "oily" spark plug(s). Bad compression could for example be a result of worn piston/ring/cylinder. What the exact cause in your case of one or more plug is oily I do not know. But you probably see the result - the outboard do not want to rev up in normal range since there is one or more cylinders not working normal.