Mercury mariner burns too rich

[Preston]

I currently am running a Mercury Mariner model 1400, 140 h.p., 1978 vintage. My problem is that with the stock plugs my engine will load up and foul the plugs. I have changed from the stock plugs to a step hotter and have checked the burn on top of each piston. Each appears to have a desirable brown tint just a shade lighter than rust--definetly not grey. My question is--the new plug is not a omni-directional firing plug. Can I do damage to my engine by using a conventional electrode plug. If so what other alternatives are there to prevent loading and fouling of plugs. I have already went to a smaller prop by the way.<br /><br />Thanks<br />Preston

 

[Solittle]

Re: Mercury mariner burns too rich

You might want to check your ignition by using a spark testor before you go to far. That would tell you if your electrical system is sending the correct charge to the plugs whatever plug you use. The spark should be bright blue and jump a gap of at least 1/2". If that is OK I would check timing to verify that the plugs are firing ar the correct point in time. If not the fuel/air charge will not detonate correctly leaving crud on the plugs.<br /><br />I assume that you clear the motor from time to time if you do a lot of trolling

 

[Preston]

Re: Mercury mariner burns too rich

When fishing, I use a small 3hp trolling motor rather than the Merc. Where I seem to have the most trouble is trying to get a tube or ski up on plane. My spark looks great and the timing is spot on. The only other variable that might be a problem is altitude. I am at 4200 feet and I am wondering about the jets for this altitude?? Is it possible to just be dumping too much fuel to the chambers??? All cylinders are burning the same as far as color is concerned. Re-propping did help and put me at about 5500rpm from 4700 but on a hot day I still get an occassional load up and bogg.

 

[DJ]

Re: Mercury mariner burns too rich

Preston,<br /><br />I'm no Merc. ecpert. At 4200 feet, you should not be running stock jets. The air's alot thinner and your putting in too much fuel.<br /><br />Perhaps someone will jump in here with the right jet size for you.

 

[Preston]

Re: Mercury mariner burns too rich

Thanks djohns19<br /><br />I think that I'll pull a jet and see what size they are. I had a local mechanic try to tell me that on this style of motor that there was just a single main jet and only in one size, however; my manuel gives me figures for different jets for different elevations. In addition, it tells me that there is a main fuel jet as well as what I believe to be an air-fuel mixture jet near the top of the float assembly. The consistency in my burn color from top cyl. to bottom cyl. indicates what I would believe to be "rich burn". If I change my jets to the correct jet for elevation, then I can go back to the stock and "colder" plugs and worry a little less about "melt down".<br /><br />Thanks for all your help and if an idea comes into mind "anyone" please help me to see the light.<br /><br />Preston in Idaho

 

[mellowyellow]

Re: Mercury mariner burns too rich

what type fuel/oil are you using in her?

 

[Bear]

Re: Mercury mariner burns too rich

140 hp serial number 5088444 - 5264704 1978<br /> http://www.marinshopen.se/guide/mp/mar275.htm <br /> <br />Jet sizes for engine above:<br />Carb parts <br /> More parts <br /><br />4200 feet is 1280 meters. I have been traveling a lot at higher altitudes by carbed motorcycles. I can't remember exactly the altitude when the thin air effects the power. Maybe 4200 feet is enough. I think so.<br /><br />If you have the time you can go to Technical Forum at http://www.marinepower.com and ask the support guys, if your dealer can't help you. <br />I find it hard to belive you are the only one facing this altitude problem. If it is an altitude problem that is.<br /><br />Good luck!<br /><br />Tell us if it worked out for you.

 

[Bear]

Re: Mercury mariner burns too rich

Do a search in this section for altitude.<br />Corm says for a 15 hp Mercury:<br />Sea level to 5000ft=*<br />5000 to 7500ft=*<br />7500 to 10,000ft=*<br />*to avoid confusion as you have a 140 hp.<br /><br />FlyByMark says:<br />At 5,000 feet your producing about 75%-80% power than at sea level. Because of the loss of power you will have to reprop 1"-3" less pitch. If you do not lean out the engine your only wasting fuel, fouling plugs and carboning up the engine. Idle air bleed screws MUST be adjusted too or the engine will idle rough and load up also.<br /><br />Check it out.

 

[Preston]

Re: Mercury mariner burns too rich

Thanks for all input!!<br /><br />I am burning an oil made by YAMALUBE approved for marine outboard, I also burn the premium fuel. Just a note to add--There are two other mercury OB's in the valley that I know of and both owners experience the same thing on hot days. The one says to run with the cowling off the motor for more air flow-but the noise really takes away from the enjoyment of boating. The other guy refuses to launch his boat anymore due to poor performance. By the way, on a cool morning/day this thing runs GREAT!!! Both owners have basically the same comment. <br /><br />Preston

 

[steelespike]

Re: Mercury mariner burns too rich

Ive heard that if the fuel pump diaphram developes a hole it can cause to much fuel to enter the crancase through the pulse port.<br /> Probably would cause uneven burn though.