Spark plug gap more boom??
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Thread: Spark plug gap more boom??

  1. #1
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    Spark plug gap more boom??

    Got your attention with the boom part lol. But I pulled my plugs and they looked ideal for normal running however when I checked the gap it was a little tight around 0.4 for both. I read the manual and it calls for a gap between 0.5 and 0.6 so I adjusted to 6. I checked the valves and they were a little loose front and back, but one in the rear exhaust was on the tight side. I've adjusted to proper clearances. My issue is that Im running a bit rich and Cat bogged only on hill climbs. I would pump the peddle and it would clear out and run fine. But the motor shut down on me one a run and when I went to start it up right away I had an awesome display of flames that shot out the exhaust. Thanks Dave for yelling at me that Im on fire, but I easily doused the flame out with water. Cat fired up just fine after that and ran good back to camp. It only sputters on steep hill climbs. So now Im trying to find the problem and thought maybe that the small spark plug gap was not significant enough to burn all the fuel in the piston causing that problem? Mrbrandt has suggested I go through fuel pump and then check injectors which I am going to get to this week. Any thoughts on the spark plug while I chase down other possiblilties?

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    I've always thought the biggest problem with your car was that loose nut behind the wheel?

    Now I'm shocked to hear that you're doing maintenance! I guess a fire will do that. Of all the rides to miss!
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    The right plug gap is often a balancing act. A bigger gap can make more power, but it also takes more electrical power. As the pressure inside the cylinder increases, it takes even more electrical power to jump the gap, so a spark gap that idles well and makes good low RPM torque can cause a mis-fire at high RPM. A turbo raises cylinder pressures even more, so it is somewhat common to find that the turbo version of the same engine will have a smaller plug gap specified. (MCX doesn't mention changing the plug gap

    You are trying to solve a high-load, high speed misfire, which is exactly what too large a spark plug gap will cause. I would have left the plug gap a little short until you get the misfire figured out, then set them to the stock specification.
    Sand-n-Sea likes this.
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    Thanks Mark! I will gap down to .5 instead since everything is still apart. I should be able to get to more troubleshooting this weekend.



    Quote Originally Posted by mbrandt1402 View Post
    The right plug gap is often a balancing act. A bigger gap can make more power, but it also takes more electrical power. As the


    essure inside the cylinder increases, it takes even more electrical power to jump the gap, so a spark gap that idles well and makes good low RPM torque can cause a mis-fire at high RPM. A turbo raises cylinder pressures even more, so it is somewhat common to find that the turbo version of the same engine will have a smaller plug gap specified. (MCX doesn't mention changing the plug gap

    You are trying to solve a high-load, high speed misfire, which is exactly what too large a spark plug gap will cause. I would have left the plug gap a little short until you get the misfire figured out, then set them to the stock specification.

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    Quote Originally Posted by Jbl View Post
    Got your attention with the boom part lol. But I pulled my plugs and they looked ideal for normal running however when I checked the gap it was a little tight around 0.4 for both. I read the manual and it calls for a gap between 0.5 and 0.6 so I adjusted to 6. I checked the valves and they were a little loose front and back, but one in the rear exhaust was on the tight side. I've adjusted to proper clearances. My issue is that Im running a bit rich and Cat bogged only on hill climbs. I would pump the peddle and it would clear out and run fine. But the motor shut down on me one a run and when I went to start it up right away I had an awesome display of flames that shot out the exhaust. Thanks Dave for yelling at me that Im on fire, but I easily doused the flame out with water. Cat fired up just fine after that and ran good back to camp. It only sputters on steep hill climbs. So now Im trying to find the problem and thought maybe that the small spark plug gap was not significant enough to burn all the fuel in the piston causing that problem? Mrbrandt has suggested I go through fuel pump and then check injectors which I am going to get to this week. Any thoughts on the spark plug while I chase down other possiblilties?
    Sorry for that, we should have let it burn...
    Jbl likes this.
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    It's better to run a tad rich under boost Joey. Less chance of damaging the engine. on the flip side, plugs need to be cleaned more often and maybe run some combustion chamber cleaner through now and then.
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    Are you running iridium plugs?
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    Hey guys, the plugs look like it was running perfect. I have never run iridium plugs and never had a problem. What I have always run are the NGK CB8RE. I just checked fuel pump pressure at Im at 45-50 psi, so if someone can help me and tell me what the tolerance is that would be great as I dont have an online manual handy. I'll be pulling the injectors off and testing them next.

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    43 psi is the spec.

    The only question about your fuel pump would be if it can still make something close to that at WOT.

    I know you want to move on to a new machine, but having an AFR gauge can be invaluable. Oh, wait. This is Jbl, so having a WORKING afr gauge can be invaluable.

    Sorry, Jbl. That was too easy to pass up.
    Jbl likes this.
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