fouled spark plugs on merc 850 - difficult to start engine

[Deeps]

I've noticed that my motor is difficult to start after about 4 or 5 trips to the lake. When I remove my plugs, there is some carbon build-up and some oil on the plugs.<br /><br />If I clean the plugs and reinstall them, the motor starts right up.<br /><br />I had my carb professionally adjusted and my motor timed last spring. I thought it was running to rich.<br /><br />Any idea of what is causing my plugs to foul?<br /><br />It's an old '76 merc 850 (rebuilt last year).<br /><br />Thanks

 

[Deeps]

Re: fouled spark plugs on merc 850 - difficult to start engine

 

[Wreck Rider]

Re: fouled spark plugs on merc 850 - difficult to start engine

Sorry I can't help you with that but maybe you can help me, what type of plugs does your motor take? I just bought the same model and year as a rebuild.

 

[papasage]

Re: fouled spark plugs on merc 850 - difficult to start engine

are you doing a lot of slow running like idling . this will foul the pluga . what is the mix . should be 50 to 1 . 16 0z to 6 galoing of gass . a outbord is made to run W O T . running slow will build up oil and foul the plugs .especialey the permagap . that is what is recomended . my 50 hp johnson uses the permagap . in a foot note it states that if it fouls from prolong idling or runs to rich and fouls the permagap use a L77JC4 or a QL77JC4 that is a resistor plug that is recomended for the newer johnson motors . . the mercuray may need anothe type dont knopw what the # is . you could have a set of bad plugs .tryb a new set and keep a fresh set in boat all the time and a plug socket even if you find the probablem . -papasage

 

[jajeeper]

Re: fouled spark plugs on merc 850 - difficult to start engine

I recently replaced my plugs with Champion L78 perma gap plugs. I found conflicting info about which exact plug number should be installed. Have heard and read L76, L77, and L78 plugs were OEM, so I don't know for sure which is right.

 

[JasonJ]

Re: fouled spark plugs on merc 850 - difficult to start engine

I never have starting problems, but I take my plugs out and wipe them off once a month, just for good measure. I do very little slow speed running, just the ten minutes it takes to idle out of my creek to the lake. The rest of the time I run at 4000 rpms, and I still get some build up. You may need to just keep 'em clean, and avoid slow speed running. I had an old 63 Merc 850 that just could not be ran slow, it would foul like crazy, but a good speed run would burn the junk off prety good.