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  1. #1
    More speed, more vert scorp jr's Avatar
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    Thumbs down Carb Settings/Fuel Starvation

    Guys,
    New problem with both a freshly rebuilt 750 and freshley rebuilt 900.

    We took both out onto the river today, everything ran fine, followed the typical warm up /break in cycle until it went wrong.

    Both boats burned a hole through one of the pistons. However, all of the carbs are freshly built and at the proper settings. It looks like there is a lean condition in both cases. My question is then should you ignore the specs for the carbs and just adjust them to fix it if you are running lean, regardless of how far off it is from the factory setting? Is there something wrong with the typical break in procedure?

    It is very odd, because on both boats the other two cylinders have great wash and seem to be fine, it is just one that gets starved and has crapped out. All fuel lines are new and updated along with oil lines.

    Any help would be greatly appreciated. I am sure my pop, Scorp, will jump in the conversation with more information as well. Thanks again.

    -steve


  2. #2
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    That sucks.....

    First, are the skis modified? That will alter jetting requirements

    Second, was a crank index done on the skis?

    What cyl was the one that burned on the skis?

    Was the restrictor installed in the 750's return line?

  3. #3
    More speed, more vert scorp jr's Avatar
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    Quote Originally Posted by xlint89 View Post
    That sucks.....

    First, are the skis modified? That will alter jetting requirements ?
    no modifications.

    Second, was a crank index done on the skis?
    No, would this cause it on only one of the cylinders?

    What cyl was the one that burned on the skis?
    Mag on the 750, PTO on the 900.

    Was the restrictor installed in the 750's return line?
    Yes.

  4. #4
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    No mods. OK

    An out of phase crank will burn 1 piston on the cyl that's out of time. However, the MAG really can't come out of phase because it's directly mounted to the flywheel. So it's possible the 900 could have. A quick crank index takes a couple minutes and costs nothing. Try that on the 900.

    Did you guys do a leak down test after the engines were assembled? Possible gasket (air) leak at the intake, carb, or cyl base. Would also show an air leak at the crank seals. Not sure on the domestics, but it's not uncommon for a Fuji engine rear crank seal to leak and burn a PTO cyl down.

    Did you guys verify fuel was flowing through all 3 carbs when running? (visual inspection)

  5. #5
    scorp's Avatar
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    thanks for the input X, leak down ok, seemed like fuel was flowing ok on 900, didn't verify on 750, will check index and flow when i replace pistons and get them running again, very frustrating though they ran great for a couple of hours the 750 wasn't to bad just a small hole in the middle,but the 900 was completely fried and damaged cylinder,now im paranoid its gonna happen again is there an easy way to check before damage is done? I was pulling the plugs about every 5 to 10 minutes to check how they were burning for the first hour of riding,thought all was ok, then just rode and after about a half hour ,it shut down pulled plugs and fried!

  6. #6
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    Can only say to check the spark plugs until you have a good wash pattern formed.

    Were you using the NGK BPR8ES in the 750? They're a cooler plug than the 7's and will give you a little more room for error.

    Is there any chance of water being in the fuel? Water can plug a carb jet.

    Are the fuel hoses kinked or plugged? (verify the hosses are clear) Also make sure pulse line is unobstructed.

    Are the clamps tight? (air leak into hoses)

    Did you check the pop off pressure?

  7. #7
    thester71's Avatar
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    Was the 750 updated with a tripple outlet fuel pump?
    My guess on the 900 would be a leaking crank seal, or a leak around the intake/reed/carb area on the pto cylinder

  8. #8
    scorp's Avatar
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    Quote Originally Posted by xlint89 View Post
    Can only say to check the spark plugs until you have a good wash pattern formed.
    ok

    Were you using the NGK BPR8ES in the 750? They're a cooler plug than the 7's and will give you a little more room for error.
    Had 7's in

    Is there any chance of water being in the fuel? Water can plug a carb jet.
    No tank was cleaned out and filled with fresh fuel

    Are the fuel hoses kinked or plugged? (verify the hosses are clear) Also
    make sure pulse line is unobstructed.
    Replaced all lines will double check for kinks

    Are the clamps tight? (air leak into hoses)
    I'll recheck those too

    Did you check the pop off pressure?
    Hmmm,no

  9. #9
    scorp's Avatar
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    [QUOTE=thester71;1420446]Was the 750 updated with a tripple outlet fuel pump?yes new tripple pump installed
    My guess on the 900 would be a leaking crank seal, or a leak around the intake/reed/carb area on the pto cylinder
    Dont think so but, I'll double check all areas

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