Shorted spark plugs!

[DIAMOND]

First time caller long time listner. Well here goes first post but not last!
I have a friend who owns one of those white motors and it keeps blowin (shorting) plugs. 91' Johnson GT200, runs great for a few trips out and then when started again missfires bad. Ohmed out plugs and found some of them shorted? Install new plugs and then runs fine again. No fouling or carbon tracking seen so this has got me puzzeled. You guys are great thanks alot!

[VectorPat]

What plugs is he running?????

[DIAMOND]

He has been running Champion plugs. Tried both gapped plugs and gapless. Don't know at this time a part number, will find out and reply later. Also this is a stock carb motor that has had the brain box replaced (REPAIR). Thanks!

[Rickracer]

I've never had Champions last more than a few months in my OMCs, but had a set of NGKs that lasted years. :cool:

[gaineso]

Different motor, but I've never been able to get Champions to last in anything, even a lawn mower.

NGK's last for years in my Tower, and I run 40:1 oil. I generally change them ever 3 or 4 years just 'cause I feel guilty if I don't. '86 Mariner 115 turning 6K+. Never heard anything bad about NGK except price.

[DIAMOND]

Thanks for the replies! I will tell him to try NGK's after he pops another set of Champions. Should we go with the gapless or the gap plugs? Motor is on bassboat that see's 40min or better at WOT. Anybody have a part number? Thanks!

[Rickracer]

...one for idling around and one for WOT, the WOT one should be surface gap, and the one I've always used. My older motors take the BUHWX1 plugs, but I would go with what the NGK book says.

[stratos]

its is your choice but i prefer gapless no electrode hanging out waiting to melt off

[gaineso]

I think the surface gap plugs are also a little better for idleing, I used to troll a lot on Lake Eufaula, and I'd run alon at about 1,000 R's or less for an hour or more. Reel in and hit it. Huge cloud of smoke and gone. No hesitation, stumble or anything else.

With the whole front of the plug wxposed, it just seems to stay clean better.

[vector mike]

Person to knock Champions. Those are the biggest pieces of S--T I have ever tried to use. I have had nothing but problems with them from fouling out to having the electrode tip fall out of the insulator. I tried to run them in lawn mowers, dirt bikes and cars and ended up tossing everyone of them. The best plugs I have found are NGK's and Bosch. Just my .02. :D

[gaineso]

Guys,

This is getting scary. WAY too much agreement. Not even any White vs. Black stuff.

Maybe we can "all get along".

[Rickracer]

With more electrode hanging out there in the combustion space, they stay hotter to burn off more of the deposits. The surface gaps don't retain as much heat, hence are less likely to cause pre-ignition or detonation. :cool:

[wrechin2]

I will agree on the champion being junk in outboards, I used to hate champions. I went to work for Chrysler and found that they run the best in our products. I have fixed alot of problems by simply taking out their new bosh platniums and putting in a set of champions. I would have never had thought it. I am a firm believer in putting in what they were made for. Would you put a ac delco in a honda? I wouldn't. Bosch= voltswagons. Ac Delco= Gm . Champion= Chrysler and so forth. Just my two cents worth:D But I do run NGK in my outboard though.:D Difference between automotive and marine.

[DIAMOND]

NGK's it is then!

Thanks Guys, I knew I would get some good answers to this question

[Jeff_G]

Just to throw some gas on the fire... I use both but favor the Champions in my race boat. Why?

When a plug is put together it is manufactured with a dry film (white) lubricant. The Champions have a tighter fit of the center electrode. They are all 2 pieces inside!!! The gap is wider on the NGK's. While fresh they are both the same but under heavy WOT the NGK's develop a gap. So the electricity has to jump this gap as well. The Champions are more resistant to this gap forming and the resultant carbon build up.

We use an ohm meter after every race on each plug. Take a hammer and break a few dozen of both and see.

On a 91 200 the standard plug is a QL77JC4, if fouling problems use a QL16V. Or a QL78V surface gap can be used.

When you did a resistance test and found them shorted to what? Where? Doesn't make sense.

[DIAMOND]

Wow,

Look at this thread go! Jeff to give you more detail the resistance measurement was taken between the center electrode and ground. They measured between zero ohm's (shorted) and 2.5k ohm's. I would think this also would be considered a short for a plug. Unfortuanately I don't have the bad plugs in hand to do further tests. I plan on visiting my friend in a couple of weeks and I'll get the plugs. I'm going to solvent clean them and then retest them. Also examine them under a Hi-powered microscope. It just seems weird that he has run Champion plugs in this motor with no problems 9yrs, rebuilt the powerhead and replaced the "box" (REPAIR), and now it's popping the plugs. Could this be a heat thing? Motor runs hot and causes a crack to develope in the insulator? Or could it be a bad "manufacturing lot#" of plugs? Also they seem to fail after the motor has been running, shut off then restarted,....pop...misfire. New set of plugs and then runs fine again.

Thanks all for the help!

[Jeff_G]

I have never seen a plug shorted that wasn't visibly broken. I have seen some that were very carbon fouled that can give you some reading. If the motor never did it before then look at what has changed. Is the ignition in A1 shape and timed right. Is the syncronization correct? What is the quality of the fuel and oil and how much? Is the motor overheating. There are many things and you can't necessarily blame the plugs. They are simply a gateway for the electrical charge and a manner of dissapating heat in the cylinder.

[H2OPERF]

I agree with jeff need to check your ignition system, plugs usually prematurely oil foul in two strokes from rich idle or weak spark .When the motors idle rich and you shut down the plugs are saturated the fuel evaporates and the oil fouls the plugs.I would check the stator resistance and output on that motor if you have or know someone with a peak meter you can check the stator output and pack output to the coils and check for proper output voltage, when the stator resistance on those engines gets down around 800 ohms or less the spark gets real weak. Dave