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WHAT THE PROPER PLUG GAP FOR 618

in 2 Stroke Technical Questions 13 years ago
Gentleman can anyone advice the proper sparkplug gap for a 618? I start to have about 300 degrees diference between the EGT readings and I want to start trouble shooting from the plugs, ANy other advice will be apreciated.
Regards to all
Yanis

  • Re: WHAT THE PROPER PLUG GAP FOR 618

    by » 13 years ago

    Yanis,

    If I remember correctly, the gap is .020" (.5mm). You might want to check the EGT probes To make sure it is an engine problem and not an instrument problem. Easiest way is to switch the position of the probes in the exhaust manifold. If the instrument readout difference reverses, the probes are OK. If the same cylinder reads high after switching the probes, the probe or wiring is bad. If the probes are OK, It is almost always a carb problem since each carb runs one cylinder.

    Bill.
      
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  • Re: WHAT THE PROPER PLUG GAP FOR 618

    by » 13 years ago

    Hi Bill and everyone else,
    Thank you for the last advice, I did chAnge the sparkplugs, gap at 19,( AS i BEEN ADVISED THAT THE ENVELOP IS 16-20 Still had on EGT reading about 200 degree differnce, I switched the EGT probes and the numbers reversed and based on what you mentioned that means that the probes are okay am I right?? Now I don't know what to do next, Cooling temp normal, CHT are matching and on the normal side, only the EGT READING IT DRIVES ME CRAZY, I checked the small screws on the carburators they both are at
    1 1/2 turn from the complete stop.
    REGARDS
    YANIS :(
      
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  • Re: WHAT THE PROPER PLUG GAP FOR 618

    by » 13 years ago

    Yanis,

    Sounds like the probes are OK. I have a couple of questions. Are the EGTs 200 degrees off at idle, midrange, and top end,or are they off at a certain spot in the throttle range. The reason I ask is that that all other settings being OK, the idle screw determines fuel mix at idle, the needle jet and needle control the mix in the midranges, and the main jet determines the full throttle mix. If the high reading is through the whole throttle range, check the throttle slide opening and make sure both slides are exactly the the same opening at idle. I use a feeler gauge and set the air screws so both slides are the same height. Then have someone slowly open the throttle while you observe the slides. They should both begin to move up at the same time. If they don't, adjust the cable thumbscrew on top of the carb to make them both open together. When both slides are sitting on the airscrew at idle, you should have couple of mm. play in both cables. Check this by just lifting the cable housing on top if the carbs. They should move just a little before the slides begin to move. Try the slide adjustments first and if that doesn't work, we'll check the other items.

    The cyl head and coolant temps often won't change too much when the EGTs are only 200 degrees different.

    Another thing that can cause high readings throughout the throttle range is the fuel level in the carb bowl. Carefully remove the bowls without spilling the fuel. The floats should all be the same height. The pin in the floats should be just touching the fuel. Lift the floats out and measure the fuel level. It should about 12-13mm from the top edge of the bowl with the floats removed.

    Let us know what you find.

    Bill.
      
    Report

  • Re: WHAT THE PROPER PLUG GAP FOR 618

    by » 13 years ago

    Hi Bill, Thank you for the latest,
    Before I procced I want to mention few things,On a previous day I did some run ups on the runway,
    meaning that the throttle setting was variable and so the EGT readings, During the runs I have noticed
    differnse in EGT from 150 to 350+ degrees,
    Also the Idle is not set yet as my lower at 1400 RPM it makes the motor rattle to much and I was trying to see the smoothest number around 2000RPM and set it, But having that fifferense in the #s was hard to do or make a decission.Now after aread your lstest this is what I will do tomorrow:
    I will set the Large screw on the side of the curbs the one that the slides are resting on I beleive that is the one that controls the Idle Am I correct?? If so I will set that screw and try 2200 RPM and if that is smooth that will be my IDLE, Now if I set the slides (pistons)with the large screw at 2200 and stil have difference in EGT reading how do I go about it? besides making sure that both pistons travel equaly and bowls have the equal and proper amount of fuel, is the air screw have anything to do with that at IDLE setting?
    Regards
    Yanis
      
    Report

  • Re: WHAT THE PROPER PLUG GAP FOR 618

    by » 13 years ago

    Here is a picture of the plugs as I remove them, They may say a lot to someone that knows,
    Yanis
    PLUGS4.jpg (You do not have access to download this file.)
      
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