Is this abnormal for my sparkplugs?

[ZmOz]

I have a '74 Mercury inline 6 150hp that I just got running. I cleaned up the spark plugs a couple weeks ago, (they were pretty new anyway)and since then I have run probably 20-25 gallons of gas through the engine. I took out the spark plugs to see how they looked, they all have carbon built up in a small area. (pic attached) Is this normal? Seems a little weird to me...<br />

 

[mellowyellow]

Re: Is this abnormal for my sparkplugs?

what type of gas r u using? shouldn't use more than 87 octane and make sure it doesn't contain any ethanol.

 

[The Marine Doctor]

Re: Is this abnormal for my sparkplugs?

That plug has the looks of #3or4 Plug. As you pull the plugs they should get cleaner and cleaner when going from top to bottom.<br /><br />This plug looks to be getting plenty of fuel...but is not burning it all. Which is generally the case for a Direct Charged Engine.<br /><br />The reason for the trace patter of spark is the extra fuel. That plug has been burning across the top as the fuel has been puddling at the bottom.<br /><br />Does the engine seem to perform well?<br /><br />If not...adjust the float levels, replace the restrictors under the intake ports.<br /><br />TMD

 

[ZmOz]

Re: Is this abnormal for my sparkplugs?

Yeah, the engine seems to be running great. Should I worry about this at all? I'm only using premium fuel, and that is only what I should be using in this old thing.

 

[greasemonkeyozi]

Re: Is this abnormal for my sparkplugs?

Almost all 2 cycle motors I have ever heared of calls for low octain such as 87. Make sure your fuel/oil ratio is correct. What is your motor's fuel/oil ratio anyways, 50-1?<br /> p.s. your plugs look just like mine after 5 tanks of fuel... I wouldnt worry. It aint broke, dont fix it.

 

[ZmOz]

Re: Is this abnormal for my sparkplugs?

When this engine was made I don't think they had 87 octane. In the manual it calls for 90 octane minimum, leaded. Any outboard this old runs on premium. I really wish I could use 87 octane though... I beleive mercury calls for 50:1 mix, although I usually go about 40:1.

 

[The Marine Doctor]

Re: Is this abnormal for my sparkplugs?

Use regular fuel..87 octane is fine. Run the engine with 50:1 mix...NO extra oil is required.<br /><br />TMD

 

[jdkzrt]

Re: Is this abnormal for my sparkplugs?

Sorry to disagree but this engine needs premium fuel. Using ANYTHING else WILL cause expensive problems in pretty short order (death due to detonation). <br /> Post the question in a new thread, and you will see what I mean. <br />

 

[The Marine Doctor]

Re: Is this abnormal for my sparkplugs?

JDK...sigh<br /><br />Factory recommends that the timing be retarded by 2 deg. This will take care of the problem of detonation by the reduced octane level.<br /><br />TMD

 

[jdkzrt]

Re: Is this abnormal for my sparkplugs?

TMD<br />Now how would this fellow know that?<br />As posted above, the manual calls for 90 octane (leaded) minimum, and you stated 87 octane is fine without any mention of timing change. <br />

 

[The Marine Doctor]

Re: Is this abnormal for my sparkplugs?

I rechecked the manual at work yesterday.<br /><br />Minimum requirement for old inline 6 engines is 86 octane. They also stated that Premium or super unleaded was fine. <----But they also stated that P and S were 89 octane.<br /><br />I was just a youngen back when the Lead was removed from gas and cannot remember the original octane level of Super and premium.<br /><br />TMD