strange looking spark plugs

[Blown Challenger]

I've seen alot of different kinds of spark plugs in my life but the ones in my 86 150xr2 have no ground strap,just a center electrode. Is this right? What kind of plugs are you guys runnin?

Jeff z

 

[ajgraz]

Re: strange looking spark plugs

My old 78 Merc has those, too. Called "centerfire" or "rimfire" plugs or some such thing.

 

[j_martin]

Re: strange looking spark plugs

That's the standard plug for your engine. Actually, picture a "normal" plug. Now pull the insulator and electrode back into the barrel until the tip is flush with the end, and add metal to the end ring till the gap between the ring and the tip is your plug gap (.032"). Now you have a "face firing" plug that protects the insulator from oil fouling.

Fire it with a knock you on your A CD system, and you have one of the strongest ignition systems on the planet.

 

[Blown Challenger]

Re: strange looking spark plugs

Thanks John. I just wanted to make sure some boob didn't install some weird chainsaw plug.

 

[Texasmark]

Re: strange looking spark plugs

I think they refer to them as "surface gap" and Merc smacks them with 40,000 volts in just a couple of microseconds (millionths of a second). The idea is to hit them with a fast rising voltage so that it has time to develop and jump the gap (firing the plug) before surface contaminants on the insulator bleed the voltage off. Merc and OMC both have used them for many many years. I've had them in both brands of engines and they lasted for years........however, with my current '02 90 3 cyl, I get better service out of a conventional plug that Silvertip put me onto.

Mark

 

[Blown Challenger]

Re: strange looking spark plugs

I just noticed yesterday if I put around (idle in gear) shell start to load up and eventually badly run. Now the temp gauge also says cold till I get above 1500 rpm.

 

[Texasmark]

Re: strange looking spark plugs

Don't understand what you are saying/referring to.

 

[Blown Challenger]

Re: strange looking spark plugs

I thought many it was the wrong plugs making her load up but I'm pretty sure that by in not getting warm,that's why she's loading up.

 

[ajgraz]

Re: strange looking spark plugs

"Surface gap", thanks, Texasmark.

In my experience old 2 stroke Mercs don't like to idle or putt around for very long. They are also finicky as to the idle A/F setting and you have to tweak on that depending on the temperature/weather (lean out a bit, maybe 1/4 turn, in the heat of the summer vs your optimum "cold" setting). Also in my experience their carbs like to get gunky. When's the last time you cleaned the carbs?

 

[Blown Challenger]

Re: strange looking spark plugs

I just got the boat last month and from what I've seen so far he hasn't done much maintain on the motor. I replaced the impeller,pulled offbthe heads and checked the cylinders and pistons and replaced t stats. Haven't dug into the carbs yet. Also its a 150hp on a 17' capri bow rider now shouldn't the thing get up and go like a raped ape? Ie doesn't feel like it does.

 

[j_martin]

Re: strange looking spark plugs

Service the poppet valve on the starboard side. You'll be good to go on the warmup.

Since it's new to you, you should start at the top with a compression test. No amount of tuning is going to make a weak motor go. If that's good, the rest is relatively easy.

It should go pretty good on that boat. Base motor is a strong 150, closer to 160.

 

[Blown Challenger]

Re: strange looking spark plugs

Comp is good John. 110 was lowest and 120psi was highest.I took apart the popit like you sugjested earlier but I don't see anything wrong with it.I'm going to the boat shop this am,ill see if they have one in stock and just replace it.