Spark plug evaluation PICTURES

yoster

Petty Officer 2nd Class
Joined
Aug 19, 2010
Messages
117
Re: Spark plug evaluation PICTURES

Ok after looking again, it does seem a little closer than the others. I still think thread length looks normal, but I'll defer to what others have said; you really need to take a look at the top of the cylinder to see if there are any marks and confirm if it's hitting or not.
 

Lostfisher

Petty Officer 2nd Class
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Nov 2, 2009
Messages
147
Re: Spark plug evaluation PICTURES

Take all the plugs out of the motor now get a wooden dowel and a sharpie. Stick the dowel down the cylinder hole and turn over the motor until the piston reaches its maximum stroke length. Mark the dowel with the sharpie an do this for all the cylinders and see i there is any diffrence in the marks on the dowel.

But i would have to agree with a bad plug.
 

RogersJetboat454

Commander
Joined
Jul 9, 2010
Messages
2,964
Re: Spark plug evaluation PICTURES

+ another on the broken porcelain.

If you look at the distance that the porcelain extends out of the body of the plug in question VS the other plugs, you can definitely tell that the porcelain appears as though it has moved.

But why?

I would make sure you do in-fact have the correct plugs and give another one a shot.
 

Tim Frank

Vice Admiral
Joined
Jul 29, 2008
Messages
5,333
Re: Spark plug evaluation PICTURES

Wonder if they are all the same type and spec plug.
The oddball looks like a projecting insulator type....say an NGK.
 

mbecke2

Petty Officer 3rd Class
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May 24, 2009
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Re: Spark plug evaluation PICTURES

So I changed the plugs put all brand new QL77JC4 and no difference. Gets out the whole quick and runs strong for about 5 seconds then drops to 32mph and runs at 32. Used to run 43mph. I tried pump the fuel ball and it seemed to help somewhat but just not a sure proof diagnosis. Still has a miss at idle (lean sneeze). Pulled plugs and all look ok except cylinder 3 plug is black and sooty. Checked spark and getting good spark on cyl 3. Not sure if it is a fuel problem or ignition. I hate to throw more money but I am so close to the fix. Any suggestions on what to do next? I am goin to try a different fuel pump from a 110 johnson, but I dont think it has enough power to deliver sufficient fuel to run the big looper with 4 seperate carbs. I will update.
 

Thompy_04

Petty Officer 1st Class
Joined
Jun 16, 2004
Messages
215
Re: Spark plug evaluation PICTURES

I just finished rebuilding carbs on my '79 150 my #2 hole plug was dry and sooty and it ended up being a carb problem. Even though I cleaned it, not good enough I suppose. Cover the carb with the sooty plug or choke it at idle see if your problem goes away, if so you've found your culprit.
 

Tim Frank

Vice Admiral
Joined
Jul 29, 2008
Messages
5,333
Re: Spark plug evaluation PICTURES

There are a number of questions/suggestions that you appear to have ignored.
People will tend to tune out if you don't respond to their efforts to help.

Were all the old plugs exactly the same brand/spec?

Did you actually mean that EVERY plug that went into #3 ended up with the gap closed down or was that an aberration?

etc.....
 

Silvertip

Supreme Mariner
Joined
Sep 22, 2003
Messages
28,758
Re: Spark plug evaluation PICTURES

Plugs that get that black in such a short time are getting way too much fuel -- not too little. That also does not account for the plug damage. A more accurate way to tell if you have a bearing issue on that cylinder is to use a dial caliper that measures depth (has a wire sticking out of the opposite end) as well as outside and inside diameter. Extend the wire with the engine turned to the bottom of the stroke. Insert the wire into the cylinder with the base the caliper on the head. Rotate the engine to top dead center and record the reading. Rotate that cylinder to bottom dead center which takes out slop in the bearings in the opposite direction. Without turning the engine, insert the wire and take the reading with the base of the caliper on the head. Repeat the process on the other cylinders. If The bad cylinder has the same readings as the others the problem is not mechanical. If it is drastically different, that cylinder has a mechanical issue. Weak spark cannot handle high loads so a very rich mixture coupled with weak spark can "put out the fire" so to speak. At this point you are "shot gunning" hoping you hit something. How about some real troubleshooting. Just because you replaced parts does not mean they are working. Troubleshooting proves or disproves that.
 
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