Checking spark plugs on Big Twin

[baytonemus]

I've got a couple of questions about the plugs on my Big Twin. When should I inspect them and what do I want to see? I guess I don't know if expectations are different for a 2 cycle motor than a 4 cycle. I've been attempting to tune this motor but I'm not really sure what I'm doing, to be honest. I pulled the plugs Sunday after a couple of hours of hard running on the lake the day before and they both looked a little oily. All ignition parts, plugs, and plug wires are new. Points are gapped at .020.

Thanks.

 

[kfa4303]

Re: Checking spark plugs on Big Twin

HI baytonemus. No worries these old gems are pretty easy once you get the hang of them. Here's a great link that should be just what you need. You can get virtually every part you may need right here at iboats too. A carb kit, points/condensers (tune up kit), water pump (impeller), spark plugs and wires should all cost less than $150, and they're worth every penny. Feel free to ask tons of questions. Keep us posted.

http://www.duckworksmagazine.com/04/s/columns/max/24/index.cfm


http://www.duckworksmagazine.com/04/s/columns/max/24/index.cfm

 

[baytonemus]

Re: Checking spark plugs on Big Twin

Thanks for your reply. Not sure if you read my whole post, though. I have already replaced all ignition parts with new. I've also salvaged a different shaft and other LU parts and completely rebuilt that, the water pump, and the carburetor, plus multiple other repairs - controls, cables, steering, etc. Can't even remember when I passed the $150 mark...

Anyway, my question today is about evaluating the condition of the plugs.

 

[kfa4303]

Re: Checking spark plugs on Big Twin

Plugs should be dark in color almost black, but not wet. If they're very grey the motor may be running lean. Very black and wet, too rich. Check out this link. It has great descriptions and pics of all types of good, bad and ugly spark plugs. Hope it helps.

http://www.theultralightplace.com/sparkplugs.htm

 

[baytonemus]

Re: Checking spark plugs on Big Twin

Thanks again for your reply, kfa. Your link was to an ultralight aircraft page. Out of curiosity, are those 2 cycle engines?

 

[kfa4303]

Re: Checking spark plugs on Big Twin

I believe so, and the symptoms of the various spark plug problems are more or less the same. While color can be somewhat subjective the wet/dry factor is less so. When you say "a little oily" that's not necessarily unexpected. These old motors do run a little dirty, so some unburnt fuel/oil mix is to be expected. What are mix are you running anyway? Should be 24:1 or even 16:1 with Champion J6C spark plugs gaped at .30 some folks go to .35, or you can go to a J8C, which is one notch hotter. 2-stokes are dirtier, but much easier to fix and maintain, which is why so many folks here like them so much.

 

[kbait]

Re: Checking spark plugs on Big Twin

If your motor is a '63, I'd run 50/1 and j4c's (j6c's excessive trolling at low idle). I've heard from those wiser than I in this forum that your motor does indeed have 'modern' needle bearings on the crank, and 50/1 is enough oil. Older bronze bushing type bearings NEEDED more oil. I heard '61 and after had roller bearings anything over 7.5hp.

 

[nwcove]

Re: Checking spark plugs on Big Twin

that motor is almost 50 years old, even with needle bearings id feed it oil at 24:1. carry some plugs with you. black and dry on the plugs, smokey running is good for that vintage motor.....plugs are cheaper than pistons.....just my 2 cents worth.

 

[JB]

Re: Checking spark plugs on Big Twin

I don't think the type of bearings are the only thing that caused OMC to say that all OMC engines built before 1964 should use 24:1. That is what I would do.

OMC said to use Champion J4C plugs gapped at .030". They did tend to foul when used for extended trolling. OMC later said it was okay to use J6C for extended trolling and that has become the most commonly used plug, gapped at .030". People who weren't around back then now think the J6C was the original plug. DO NOT use J8C, that is a lawnmower plug and far too hot for a water cooled outboard.

So, were it mine, I would use 24:1 fuel and J4C plugs gapped at .030" to .040" to taste.

 

[nwcove]

Re: Checking spark plugs on Big Twin

good call jb, i missed the j8c in the mix. that would probably cause more harm than good. run it rich, cold spark and it will stay running.

 

[baytonemus]

Re: Checking spark plugs on Big Twin

Thanks for the replies, guys...PLUS, the venerable JB himself posting to my thread. Cool!

I've been running synthetic oil at a mixture of 32:1 for two reasons: First, the only OB motor shop here that will still work on older motors (and has been doing so for a LONG time) recommended it; Second, I think I recall someone on this list (FR maybe?) posting a technical document Evinrude sent out back in the 60s saying a lower ratio was OK. (Did I dream that?) That is not to say that I couldn't be persuaded otherwise.

As for plugs, I've got NGK B6S installed at the moment. I assume that these are the equivalent of the J6C? JB, maybe you should send a note to the iboats store people, because they recommend the RJ8C for all 40hp models of this vintage. On the NGK side they say B8S for the Big Twin and B6S for all other 40s from 1956-1973.

What do you gain by widening the plug gap? Thanks!

 

[JB]

Re: Checking spark plugs on Big Twin

I am a stubborn old coot. OMC designed those engines to use Champion plugs and always recommended Champions.

I do not accept claims of equivalency. There is nothing wrong with NGK, AC or Denso plugs. OMC said Champion so I say Champion.

Use whatever fuel mix you choose. It is harmless to use more oil than the maker tells you to.

 

[baytonemus]

Re: Checking spark plugs on Big Twin

I am a stubborn old coot. OMC designed those engines to use Champion plugs and always recommended Champions.

I do not accept claims of equivalency. There is nothing wrong with NGK, AC or Denso plugs. OMC said Champion so I say Champion.

Use whatever fuel mix you choose. It is harmless to use more oil than the maker tells you to.

Ha! I'm going to embrace my inner coot, too! I'll try running the Champion J6C plugs. It sure doesn't cost much to replace plugs.

I appreciate your observation about the oil. I definitely am not comfortable with the idea of 50:1 on that motor. I just figured that if I can keep a little extra oil out of the lake and atmosphere without risking damage to the motor, I'd like to do so. Has anybody seen that technical document from Evinrude that I referred to?

Thanks again!