Mercury 850 looses power after warm

[jajeeper]

I ran the outboard on the used boat I bought for the first time this past weekend. See signature for specs. After getting it started it idled good and ran great for the first 15 minutes. I could go from idle to WOT with no hesitation and no problem. Then, it got to where it would idle fine and would run up to about 1/2 throttle just fine, but beyond that it sounded as if it was either starved for fuel or flooding out. I checked fuel lines and bulb and couldn't find any visible signs of problems. A friend of mine suggested replacing spark plugs and wires for multiple reasons. He says if I don't know when they were replaced last, it probably needs it. Plus, he says when spark plugs fail, sometimes they only show signs of problems once hot. Does this sound reasonable? Any other things to check?<br /><br />Also, concerning replacement spark plugs. The reference I found online lists Champion plugs, p/n: 5898. However, the parts store cross referenced that number to a Champion L76V. Upon further research I found that the 5898 plugs are designed for CDI ignition systems where the points have been replaced with electric circuitry, while the L76V plugs are just regular resistor plugs. It says not to use a regular resistor plug on engines with CDI. Does my outboard have CDI or points? Does anyone know from the service manual the exact plug that it calls for?<br /><br />Thanks for all the help.

 

[emckelvy]

Re: Mercury 850 looses power after warm

L76V's were OEM-spec in many inline 4 and 6 Merc's and your 850 wouldn't have a problem with them. According to my old Seloc manual your motor originally came with L78's, which are a hotter plug than L76's. But even with L-76's it should run OK.<br /><br />Your motor has CDI ign but I suspect the info you're looking at is more for OMC products than Mercury. Surface-gap plugs were original equipment on these.<br /><br />It's possible you may have a bad plug, and it might be worth throwing a new set in. Most auto parts stores carry them or a substitute brand such as AC or NGK.<br /><br />Don't bother replacing plug wires unless you can see them sparking/arcing at night. They are metal-core wires and the cores don't break down.<br /><br />You may have issues with the carbs or fuel pump, expecially if the motor's been sitting for a while. Or you could have problems with the tank, vent, anti-siphon valve, or water contamination.<br /><br />Maybe sample the fuel and check the fuel filter screen(s) in the motor. You'll either have one screen in the fuel pump that's mounted on the lower cowling, or (if you have pumps mounted on the motor), the screens are atop each carb. <br /><br />HTH.........ed

 

[jajeeper]

Re: Mercury 850 looses power after warm

OK...so I changed my plugs tonight with L78s as the Seloc manual recommends. When removing the old plugs, I see that the top cylinder had an L78 in it and the other three had L76s. Any mechanical reason someone would have done that, or you think did someone just probably put in what they had or could find easily? Would the plug mix have caused any issues?