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  1. #1

    Spark Plug question

    2001 XA 800. Just put the rebuilt engine back in. Carbs were also rebuilt. Ski runs normally out of the water but only goes to 4000 rpm in the water. Here's what the new spark plugs look like after 20 or 30 minutes of use. The plug from the front cylinder looks barely used? And would it be normal for the rear plug to look fouled due to 32:1 mix for break in? I appreciate any help.
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  2. #2
    Happily Self-Employed WFO's Avatar
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    not a very good pic

    need more history...

    compression readings? recent rebuilt motor? what craft?

  3. #3
    Yamaha artisan Cutlass's Avatar
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    Quote Originally Posted by blackkev View Post
    2001 XA 800. Just put the rebuilt engine back in. Carbs were also rebuilt. Ski runs normally out of the water but only goes to 4000 rpm in the water. Here's what the new spark plugs look like after 20 or 30 minutes of use. The plug from the front cylinder looks barely used? And would it be normal for the rear plug to look fouled due to 32:1 mix for break in? I appreciate any help.
    Actually the front plug looks normal and the rear plug is showing where the issue is. The plug should not foul that badly, that quickly with 32:1 mix for break in. Its hard to say exactly but looks like the rear carb is just dumping gas in....way too rich.

  4. #4

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    Not enough running time to tell everything yet. I am doing my breaking in right now and read a lot of post about the reading of the plug.
    1) the second on is way too rich.
    2) first one may be lean but need a little more time to see the result.
    I will adjust the back tone leaner and front to be reacher. The reason for adjusting the front one is that it is better to start rich then lean out.
    Btw it is a two cylinders did you sync the carbs? I think the pop off need to be within 1 psi.

  5. #5
    Oside Bill fixed the carbs, so I'm sure they're not the issue. The engine runs off just the front cylinder but not off the back one, even though spark and compression is fine. Would a faulty temperature sensor on the stinger pipe cause one cyliner to not fire?

  6. #6

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    check CDI.

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    Yamaha artisan Cutlass's Avatar
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    Quote Originally Posted by blackkev View Post
    Would a faulty temperature sensor on the stinger pipe cause one cyliner to not fire?
    Maybe, but I don't think so. Is there a reason you suspect the temp sensor has a problem?
    Black and sooty just screams RICH RICH RICH. Is it possible the choke on that carb is misadjusted and partially on? or any other reason why that carb would run richer? Maybe something got in the carb and is sticking the needle open?

  8. #8

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    Just to check, on most of the twins, both cyl spark at the same time, off of the same coil. You could try swapping plug wires to see if it makes the other cyl not work. It is not uncommon for a coil to go bad on one side, or the plug wire to break down internally, sometimes it makes enough spark to run on the trailer, but not enough to fire under load, like in the water.
    Just checked, your 800 does use just one coil for both cyl, so probably is NOT cdi or temp sensor. Swap plug wires to opposite cyl and see if problem moves.

  9. #9
    Thanks for all the help. I swapped the plug wires, and the front cylinder will run off either wire, while the rear cylinder won't run off either wire. So I guess spark is fine. Could I have done damage running it in the water for 30 minutes with one cylinder not firing?
    Not sure if it means anything, but when I take the plugs out and shine a light down, the front piston looks brand new with a light film of light greyish fluid while the back one looks dry and burnt.
    I'll have to find someone who can look at the carb setup.

  10. #10
    So it turned out the problem was a twisted crank. Easy enough to spot, I just didn't think to check since it was just rebuilt.

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