90hp Mercury fouling the bottom plug

[lifeboatman3]

I have a 1994 90hp Mercury and the bottom spark plug keep getting very dirty. I checked the fuel pump diaphragm and it's O.K. compression if the same on all three, I cleaned the carbs and swaped the coil and it's still no better. I changed the plugs and it ran great but when I went out the second time back to the old problem of lack of power max 4500rpm and slow out of the hole and mainly running on two. <br />Please if anybody help<br />Thanks

 

[Laddies]

Re: 90hp Mercury fouling the bottom plug

You need to use a induction meter to see if you are loseing spark on that cyl and if you are a DVA to test the switch box or just take a chance and change the box

 

[lifeboatman3]

Re: 90hp Mercury fouling the bottom plug

Hi<br />Thanks for the reply. I have tried a spark tester and it's O.K and I am sure the switch box is O.K do you have any other ideas?<br />Thanks for your time

 

[Clams Canino]

Re: 90hp Mercury fouling the bottom plug

You gotta test the actual voltages - under load even. <br /><br />Weaker spark on the bottom one is the best guess. Laddies is one of the best here.<br /><br />-W