1976 merc 9.8 random rough idle

[green4themoney]

howdy guys while one of my 9.8s is being rebuilt, my other is being rather stubborn, im running it on 91 with a 40:1 mix...... i think its fouling the plugs at low idle... kinda randomly dies or run on one cylinder, gave her a full carb kit/ fuel pump im running buhw-2 plugs..... pulled the plugs out theres dark sooty thick lines from electrode to ground edge... should i maybe try it at 50:1? anybody have any input?

 

[green4themoney]

ive tried the buhw and same thing (smaller gap should have helped if the ignition was getting weak seeing as a smaller gap .052 rather than .072) my next move is to maybe try buzhw-2

 

[green4themoney]

Dont know if anybody has been reading this but tried some new buhw-2 spark plugs and mixed fuel at 50:1 dead nuts (quicksilver semi syn and shell ethanol free 91 oct) and shes runnin like a top no fouling yet... fingers crossed.