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  1. #1
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    Default Spark plug evaluation PICTURES

    1988 johnson 140 looper
    Losing power at WOT and cylinder 3 spark plug has dry black coating all over. Notice the pics as if you were lookin at motor from back. The 2 on the left are cyl 2 and 4 and the two on the right are 1 and 3. Also cyl 4 spark plug the sleeve slides up and there is no gap. Not sure why it does that. Maybe the plug is bad. I checked compression and it was 1-125 2-125 3-122 4-130. I changed all ignition parts except the timer base. I think it has a misfire on 3 but cant pinpoint the cause. Second picture is cyl 4 and 3rd pic is cyl 3. Any suggestions??
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  2. #2
    Senior Chief Petty Officer
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    Default Re: Spark plug evaluation PICTURES

    the plug with no gap is certainly not right, when you say you replaced all the ignition parts, exactly what was replaced? as in coils, power pack and so on?

  3. #3
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    Default Re: Spark plug evaluation PICTURES

    spark plug #4 is trash, replace it, or just replace all of em. The rest look OK to me, but the detail pic of #3 is not too clear.

    I bet if you get rid of that #4 faulty plug your problems will go away.

  4. #4
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    Default Re: Spark plug evaluation PICTURES

    I replaced stator, ppack, coils, wires, plugs. It doesnt matter if I put a brand new plug in cyl3 it will always come out looking like that (black dry soot). I know that cyl has a problem but cant figure out what it is. The plug with no gap is wierd it seems like any plug I put in there seems to come out like that even if it is gapped before, but maybe Im wrong. Maybe just the sleeve is loose on that plug. I think the problem is cyl 3 becauze no matter what I do that plug always always always looks like that.

  5. #5
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    Default Re: Spark plug evaluation PICTURES

    Quote Originally Posted by mbecke2 View Post
    The plug with no gap is wierd it seems like any plug I put in there seems to come out like that even if it is gapped before, but maybe Im wrong.
    Piston is hitting the plug(bad rod bearing)
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  6. #6
    Supreme Mariner Silvertip's Avatar
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    Default Re: Spark plug evaluation PICTURES

    Under what conditions was the engine run when you pulled the plugs. Unless you make a long wide open throttle run and then immediately chop the throttle and pull the plugs to read them you will never get a good reading. Idling for long periods on a two stroke can mess up the plugs. It would appear that the engine is running very rich so you likely don't have an ignition problem but rather a carburetion problem. As for the plug with no gap, of course something is wrong on that cylinder. Look into the spark plug hole with the piston at top dead center. I think you will see a mark on the piston where it has been hitting the plug.

  7. #7
    Chief Petty Officer JSGOLD's Avatar
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    Default Re: Spark plug evaluation PICTURES

    Maybe the cylinder is full of carbon???

  8. #8
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    Default Re: Spark plug evaluation PICTURES

    Seems like some strong compression numbers on that engine. Any chance the heads have been cut or replaced?

  9. #9
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    Default Re: Spark plug evaluation PICTURES

    I seriously doubt there is anything wrong with the plug that is closed, there is something going on that is closing it up, bearings would be very noisey if they were that bad, I reckon you would hear it easily, more like the head has been machined and it is now too close, or the wrong heads are fitted, you need to fix that problem long before you worry about a cylinder running rich! trust me on that one. It may be possible to perhaps fit a couple of extra washers under the plug to space it out a bit, but it is not fixing it, just covering the problem.

  10. #10
    Vice Admiral bktheking's Avatar
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    Default Re: Spark plug evaluation PICTURES

    The no gap plug is defective, the insulator has broken, discard immediately.
    Signature- If you have fuel and spark- Have you checked compression?

  11. #11

    Default Re: Spark plug evaluation PICTURES

    I'm with bktheking, center electrode insulator has broken and slid up. If something hit the negative electrode it would be bent down toward the center electrode but it looks the same as others. Would still replace it though.

  12. #12
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    Default Re: Spark plug evaluation PICTURES

    He said every plug put in that cylinder ends up gap closed.
    Look at piston top I bet there is some intication of the piston striking the plug.
    If the bearing is that bad I think if you rock the motor with the piston in mid stroke
    you may here the bearing.Or with a screwdriver on the piston you may note a lag in its movment.

  13. #13
    Vice Admiral bktheking's Avatar
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    Default Re: Spark plug evaluation PICTURES

    Then if that's the case yes bad bearing or wristpin.
    Signature- If you have fuel and spark- Have you checked compression?

  14. #14
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    Default Re: Spark plug evaluation PICTURES

    Thanks for all the replies. I bought the motor couple years ago so Im not sure about the history- redoing heads, pistons etc. But anyway I'm goin to replace all the plugs and post back. I think the piston maybe hittin the plug as this makes since to me. I will take a look and post update. Again thanks.

  15. #15
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    Default Re: Spark plug evaluation PICTURES

    This is a 140 looper....there is no way for the piston to hit the plug...the plug does not extend into the combustion chamber, the chamber is sort of a hemisphere, and the piston is a relatively flat top. It is not like a crossflow which has part of the piston extending into the combustion chamber.

    Are you sure you are using the right plug? Should be Champion QL77JC4.

    If you have the wrong plug...threaded part too long...it may reach down far enough to hit...but it is a long way, at least 3/4".

  16. #16
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    Default Re: Spark plug evaluation PICTURES

    Looking at those pics again...it sure looks like way too much thread on those plugs. I bet you have the wrong ones in there.

  17. #17
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    Default Re: Spark plug evaluation PICTURES

    certainly looks like the insulator has slid up towards the prong on the plug!!! there is twice as much showing on the bad plug as there is in the other three...seems pretty clear.

    plugs are cheap


    bob

  18. #18
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    Default Re: Spark plug evaluation PICTURES

    Quote Originally Posted by mbecke2 View Post
    I replaced stator, ppack, coils, wires, plugs. It doesnt matter if I put a brand new plug in cyl3 it will always come out looking like that (black dry soot). I know that cyl has a problem but cant figure out what it is. The plug with no gap is wierd it seems like any plug I put in there seems to come out like that even if it is gapped before, but maybe Im wrong. Maybe just the sleeve is loose on that plug. I think the problem is cyl 3 becauze no matter what I do that plug always always always looks like that.
    But he says that any plug he puts in there comes out the same way; how is he breaking the insulator loose unless wrong plugs to begin with.

  19. #19
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    Default Re: Spark plug evaluation PICTURES

    He has the wrong plugs. He should have QL77JC4s. The "L" in QL77JC4 means 1/2" thread reach.
    Look at the width vs the length in his pics. A width of 14mm is just over 1/2" wide. But in his pics, the reach is longer than the width of his plugs.

    He has about 1/4" too much sticking through the top of the combustion chamber.

    Well, that's what it looks like anyway. Please post the plug type you have in the pics. I don't see that anywhere in here....

  20. #20
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    Default Re: Spark plug evaluation PICTURES

    I don't know, those look about the same thread length as my looper..

    I don't think the gap is actually CLOSED on that plug. I think the insulator just slid up, that's it. I don't think anything is actually bent. Compare the distance from the ground electrode to the start of the threads on that plug to the others; it's the same. The only difference is the insulator that has broken and slid up. I'll bet if you slid the insulator back down again where it's supposed to be, it would look normal.

    How many plugs have you tried in that cylinder? Are you absolutely sure they all have come out like that, or do you just think they have all come out like that? Is it possible that the first one was actually gapped too close by the previous owner, and then this one is an actual defective plug with a broken insulator (making it look like the same problem)?

  21. #21
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    Default 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.

  22. #22
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    Default 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.

  23. #23
    Commander RogersJetboat454's Avatar
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    Default 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.
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  24. #24
    Captain Tim Frank's Avatar
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    Default 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.

  25. #25
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    Default 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.

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