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  1. #1

    99 slth help needed

    Hi everyone, I am hoping for some advice. I am on vacation with my SLTH for the week. Its a 99 with the red US 2 cyl engine. Its been running great since i did the ignition upgrade with the help of this forum a couple of summers ago. Yesterday out on the water at full throttle it started stumbling and it less then a minute the stumbling got worse and now it barely runs. Its seems to not be firing at all on the rear cylinder as it stays cool and makes no difference if i remove that plug wire. I pulled the plugs and have good spark on both plugs. Next i checked the fuel separater, it seems clean. I dont have a compression tester with me, but cranking it with some restriction on the spark plug holes gives me a sense that compression is ok in both cylinders. At least i dont see any difference between the two. Also the draw thought both carbs seems to be about equal.

    Next step for me today is to pull the fuel lines and see if i am getting gas to both carbs. I also have some starting fluid and I am going to try that on the rear carb. I am suspicious of the fuel because the morning I had the problem I filled up with 5 gallons of gas that was in a jug at the camp I am staying at. I was told it was fresh, but I cant be sure.

    Any other ideas guys? Any help appreciated!


  2. #2
    Click avatar for tech links/info, donation request K447's Avatar
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    Bad gas normally would affect both cylinders.

    Try swapping spark plug wires to see if the cool cylinder moves to the front. If it does then the CDI or stator are suspect.

  3. #3
    Does the upgraded ignition fire both plugs simultaneously? Is there a single coil??? I dont remember.

  4. #4
    Click avatar for tech links/info, donation request K447's Avatar
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    Quote Originally Posted by Pauls slth View Post
    Does the upgraded ignition fire both plugs simultaneously? Is there a single coil??? I dont remember.
    Both spark plugs fire together every time either cylinder needs spark. There is a single ignition coil driven by the CDI that fires both spark plugs. Both spark plugs must be grounded to the engine to allow them to fire.

    But there are two Hall Effect sensors in the stator that drive two input 'channels' on the CDI. If one channel or one Hall Effect sensor fails then only one cylinder will produce power. The other cylinder will only be sparking during the exhaust stroke and will not ignite.

    Check for loose connections inside the electrical box, especially between CDI and stator wires.

  5. #5
    thanks! I swapped spark plug wires at the electrical box. No change - rear cylinder still not firing. I checked the connections in the box and they all seem solid. I am not sure what to do next. I guess it could still be the stator or CDI if there is no signal firing that rear cylinder - correct?

  6. #6
    casey67's Avatar
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    I would replace the spark plugs.

  7. #7
    thanks, i did. no change.

    At this point i think i need to do a compression test. If thats good I am thinking CDI or stator. I guess I am buying another upgrade kit

  8. #8
    RLACEMAN's Avatar
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    Always start with a compression test to eliminate mechanical problems, then go the electrical. Ignition update kit must do something different with firing both plugs at the same time. The 99 slth I worked on would only backfire through the exhaust with the wires swapped. If the front cylinder runs with either plug wire attached, then I think your electrical system is fine. Could be something as simple as a broken reed valve.

  9. #9
    I agree on the compression test, but I was away on vacation and had no tools. So I am home now. Compression checks out. I went through magneto tests located here:http://www.greenhulk.net/forums/show...87#post1110087

    This is an updated ignition. The resistance tests checked out except I had 1.0 ohms yellow to red/purple vs 0.75. BUT.... I ran a test like this...
    I cranked the engine with all stator wires connected as they should be but first the green then the red disconnected. I got spark with red but not green, and no spark with green but not red. If I am reading the wiring diagram right, thats one of the hall sensors. Is this correct? So I guess I am looking at a new stator. Any suggestions on a part number? Should I just buy the whole upgrade kit again?

  10. #10
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    I would think just the stator is available, but I bet for an extra hundred bucks or so the update kit will leave you with some spare parts to keep on hand, or sell to help recoup the cost of the repair. If you buy the update kit and want to sell any of the extra parts, I may be interested in the CDI.

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