Odd spark plug condition

A forum for discussing boat or trailer repairs or modifications that you have made or are considering.

Moderators: Catigale, Paul S, Heath_Mod, beene, Hamin' X, kmclemore, tangentair

Post Reply
Tedd
Deckhand
Posts: 34
Joined: Thu Jan 03, 2013 11:11 pm
Sailboat: MacGregor 26S
Location: Surrey, BC, Canada

Odd spark plug condition

Post by Tedd » Tue Aug 13, 2019 11:45 pm

I have a nice photo of this but I can't figure out how to attach it so I'll have to go with a description of the problem.

I'm not a stranger to reading spark plugs but I've never before seen ones like what I just pulled from my Tohatsu 8B. The plugs are squeeky clean except for carbon deposits on the anode, the very tip of cathode, and a strange stripe of deposit on either side of the insulator that looks like a fat lightning bolt. Both plugs are the same.

Anyone got a theory about this? The motor runs and makes decent power but it stumbles a bit and doesn't hold a steady rpm.

macowneril2015
Chief Steward
Posts: 92
Joined: Tue Nov 10, 2015 8:51 pm
Sailboat: MacGregor 26X
Location: Downtown Chicago, 2001 26X, 2001 50 Hp Nissan (NS50D2)

Re: Odd spark plug condition

Post by macowneril2015 » Wed Aug 14, 2019 2:30 pm

Could be a lot of things but sounds like a misfire. Have you tried replacing them?

Tedd
Deckhand
Posts: 34
Joined: Thu Jan 03, 2013 11:11 pm
Sailboat: MacGregor 26S
Location: Surrey, BC, Canada

Re: Odd spark plug condition

Post by Tedd » Thu Aug 15, 2019 10:43 pm

I tried cleaning them with varsol but it appears the pattern on the insulators is burned right in, not just a deposit. So I think you're right. I think they're cracked and arcing through the insulator. So, yes, I will replace them.

It seems very odd to me that they both cracked essentially the same way at essentially the same time. (They were installed new less than 10 hours ago.) But I can't think of another explanation.

Post Reply