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  1. #1

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    750 Stator one coil (Hi Speed) resistance low, seems like a misfire, 5000rpm max revs

    Engine will not rev beyond 5K on a 1995 SLT(there is no rev limiter). Carbs/Fuel system/triple pump/plugs/grounds/1/4" wire trim all quadruple checked OK. My Stator checks out good for ohms except the 90 ohm spec is at 67 ohms.(blue/red to red/white).
    Rick's Motorsports Electric tells me this is the High Speed Coil. This is the first time I have ever had this issue, and the first time I have been told that this particular coil is the High Speed coil. Does anyone have any experience with a similar 5000 rpm misfire? The engine runs good up to 5000 rpm then will not rev beyond that.
    Is the High Speed Coil responsible for Hi Speed rpms?? If so, when does it take over from the Low Speed coil?(if that is the case)
    Should I suspect that the CDI or the Stator or something else is the cause of the 5K rpm max issue?
    Still trying to procure a GOOD Stator in case I need to change it out to check off one item from my process of elimination. I have a good running SLT 780 from which I could swap in the known good CDI temporarily into the 750 for testing purposes, but that cdi is timed differently, would this cause an issue with the 750? Conversely, could I put the 750 CDI into the 780 to test it out?

    Running out of Lake time and would like to fix this issue while I can still water test. Any help is appreciated.


  2. #2
    Myself's Avatar
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    I've had this issue on several stators, various brands. The ac voltage output will be conclusive. While running and trying to rev it ( strapped on trailer and backed in the water) watch ac voltage output of the excitor. If the rpms increase and the ac voltage drops then the stator is at fault. If it holds steady or rises then it's working properly.

  3. #3

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    Quote Originally Posted by Myself View Post
    I've had this issue on several stators, various brands. The ac voltage output will be conclusive. While running and trying to rev it ( strapped on trailer and backed in the water) watch ac voltage output of the excitor. If the rpms increase and the ac voltage drops then the stator is at fault. If it holds steady or rises then it's working properly.
    That's great troubleshooting advice. Thanks! I will check the Exciter a.c. output and report back. The 90 ohm coil(that reads 67 ohms) is a different coil and that one is my focus. I understand the theory so i will check it also. Do you know what a.c. volts each coil should put out, specifically the 90 ohm coil?? Some here call it the Pulser coil but I believe the Pulser coil is the 220 ohm coil on the outer edge of the stator....

  4. #4

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    So this misfire troubleshooting has taken a different turn. I decided to purchase three inline spark testers, installed them on the engine and ran the machine at idle on my lift in the lake. At idle all three plugs seem to be firing fine as confirmed by the the visual indicators, but when I reved it Beyond 3000 RPM a misfire occurs on the center cylinder, on the spark tester it starts to flicker then almost entirely disappears in brightness at 4000-4800 rpm compared to the other two which are very steady and bright. Every time I release the throttle back to idle the center plug indicator glows bright red again just like the other two cylinders. Am I safe to assume knowing that the stator supplies the signal to the CDI which fires all three coils at once that only the center cylinder ignition coil is defective and that the stator and CDI are fine? Perhaps I am overthinking this but could the CDI or stator be weak such that only two of the coils are able to fire and the third coil which is I assume in the worst condition of the three has trouble firing? I have ordered a coil, will install it later this week and trailer test afterwards. Would like to hear from anyone who has experienced a similar situation, I'll report back soon as I can. I have a video ( see next post) that clearly shows the center plug is misfiring. Also, the center piston is very wet after running these test for 10 or 15 seconds, as would be expected.
    Last edited by waterpest; 09-17-2018 at 02:40 PM.

  5. #5

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    Was able to upload on YouTube, the video start at WOT but only around 4800 RPM is the maximum I can achieve, shows a misfire, when I release back to an idle we can see the misfire all but disappears

    Last edited by waterpest; 09-17-2018 at 02:41 PM.

  6. #6

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    Quote Originally Posted by waterpest View Post
    That's great troubleshooting advice. Thanks! I will check the Exciter a.c. output and report back. The 90 ohm coil(that reads 67 ohms) is a different coil and that one is my focus. I understand the theory so i will check it also. Do you know what a.c. volts each coil should put out, specifically the 90 ohm coil?? Some here call it the Pulser coil but I believe the Pulser coil is the 220 ohm coil on the outer edge of the stator....

    Mylself...I did not test the Stator A.C. outputs as I strayed off into ignition coil testing with spark plug testers. See the above post and video.

  7. #7
    Myself's Avatar
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    Seems like a bad coil, unhook all 3 and ohm them out. Do they ohm around the same values?

  8. #8

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    Did you try wrapping a heavier gauge bare copper wire around each metal base on your spark plugs and then grounding it as I had suggested. That fixed my problem when I had a cylinder that wasn’t firing properly. Also did you switch plug leads between the PTO and Centre cylinder to see if the problem followed the lead?

  9. #9

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    I had checked the primary side of all 3 earlier this Summer, they were all the same. I will check again tomorrow

  10. #10

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    SeaBee63 No I have not tried the copper wire grounding. I did swap PTO and Centre wires and the issue followed. This means it is not a grounding issue then?

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