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  1. #1

    Exclamation 95 SL 650 fouling plugs/stalling after 50% throttle

    So I've got my 95 SL650 starting up and idling like a champ on the trailer. The first time I went to put it in it would stall as soon as it fired up so I had my mechanic come out and work on it and we've gotten it to a point where it will start and run mildly as far as throttle but as soon as you try to really get on it, it dies out but can be started back out. My mechanic found that the plugs were getting fouled after a few attempts and after an hour or so of pure tuning while on the water we still had no luck as far as getting it run perfectly. Below I listed all the parts and things I've had done to it this far below:

    -All new fuel lines and fuel filter
    -Brand new battery
    -3 new sparkplugs
    -New fuel pickup/sender at the tank
    -New gasketmaker seal at the base of the intake on the block
    -New stainless steel starter switch
    -New Jet Logic key
    -Venom 3 carb rebuild kit including jets, springs, diaphragam, etc
    -New fuel lines between the carbs


    I'm really hoping you guys have some suggestions because at this point I really cant figure out whats going on with it. My mechanic had the idea to put the original springs in and possibly some other options but I wanted to check with the pros of Green Hulk first!

  2. #2
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    Engines start easily on the trailer as there's no load on it and require little fuel. (like neutral in a car) When you start it in the water, it has a load and generally requires more fuel. So your idle air mixture screws are off, or you just need to simply turn up the in water idle screw to raise the RPM to whatever spec is. (prob around 1100 RPM) Normally the engine will run around 3600 RPM when on the trailer and about 1100 RPM in the water when tuned in correctly.

    An abrupt shut down at speed is normally a lack of fuel or cold piston seizure.

    When you say the spark plugs got fouled out after a couple attempts, how were they fouled? wet and oily? or just a dry black carbon look?


    Is this boat running premix fuel, or are you using the oil pump?

    What fuel/oil ratio are you using if premix? Did you mix it well before putting it in the boat if premix?

    We had a guy dump oil into his gas tank before adding fuel once and it never mixed well. He kept (oil) fouling out spark plugs.

    What spark plugs did you install? NGK BPR8ES gapped at .028" is what you should have.

    When you attempt to accelerate, try closing the choke a little bit and see if that helps. This will richen the mixture and help identify a lean air fuel. (needing more gas)

    NOTE: do not ride around with the engine in this condition, you will cause engine damage if you are not getting sufficient fuel.

    Let's address your list:

    What fuel filter did you replace? Does your ski have the fuel filter water separator? Or is it just the water separator? (the filter separator has an orange ring and SS mesh cylinder in it. The separator only is just the clear bowl)

    What spark plugs did you install and what were they gapped at?

    New gasket maker seal at the base of the engine block? I'm confused on this one. You should have a gasket, the reed block, gasket, then intake manifold.

    Venom 3 carb rebuild kit? How about a link to this? I've never heard of these. They include jets? What size, and did you install them? We recommend only genuine Mikuni carb rebuild kits.

    1. Make sure your throttle cable is not hanging up and have about 1/8" of play on your throttle lever.

    2. Make sure your carbs are sync'd. Meaning all 3 throttle plates are working in unison and opening at exactly the same time and the exact same amount. There are adjustment screws to do this. The instructions are in the Mikuni manual of post #7. Fuel Fuji Carbureted (greenhulk.net)

    3. What jets were installed?

    4. Was pop off pressure checked?

    5. Are the low idle speed adjustment screws good? Best way to achieve this is to leave the ski strapped to the trailer and back it in. Start the engine and get it up to normal temp. Adjust the idle speed screw to get 1100 RPM. Now turn the idle mixture screw (mounted low on the carb) in and out of the MAG cylinder to achieve highest RPM. Make 1/8 turn at a time and wait for the engine speed to correct itself. Adjust the idle speed screw to get back to 1100 RPM. Then do the same for the CEN cyl. Adjust the idle speed screw again to maintain 1100 RPM. Now do it for the PTO cyl. Doing this should get you the best/smoothest idle and take off.

    If you find turning the low idle mixture screws all the way in get best results, you have too big of low speed jets installed.

    If turning the screws out more than 2 full turns from a LIGHTLY seated position gets you the best results, you need a larger low speed jet installed.

    The hi speed adjustment screw (mounted high on the carbs) is for WOT tuning. When it comes to this, it's best to start out with too much fuel and take it away to achieve proper supply. So I'd suggesting starting at 2 full turns out from a lightly seated position and watch your RPMs and/or piston wash for proper fuel supply.

  3. +1 by:


  4. #3
    does it "load up" before it dies?

  5. #4
    Load up meaning increase the RPM as I give it more throttle?

  6. #5
    What fuel filter did you replace? Does your ski have the fuel filter water separator? Or is it just the water separator? (the filter separator has an orange ring and SS mesh cylinder in it. The separator only is just the clear bowl)
    -The filter I replaced was the bucket style that was the factory one for an in-line fuel filter. I believe the kind I'd replaced was the separator style. I didn't think that would have an effect on fuel flow


    What spark plugs did you install and what were they gapped at?
    -Not sure to be honest. My Mechanic grabbed them. They could be anything but I asked him.


    New gasket maker seal at the base of the engine block? I'm confused on this one. You should have a gasket, the reed block, gasket, then intake manifold.
    -The gasket at the intake manifold between it and the reed block. It disintegrated when he checked it.


    Venom 3 carb rebuild kit? How about a link to this? I've never heard of these. They include jets? What size, and did you install them? We recommend only genuine Mikuni carb rebuild kits.
    -It was a kit I'd found on Amazon that was cheaper but still had good reviews as far as use. Now I'm starting to think it's the problem.


    1. Make sure your throttle cable is not hanging up and have about 1/8" of play on your throttle lever.
    -Good idea. I want to say it has a bit of play on it but I could be wrong as well


    2. Make sure your carbs are sync'd. Meaning all 3 throttle plates are working in unison and opening at exactly the same time and the exact same amount. There are adjustment screws to do this. The instructions are in the Mikuni manual of post #7. Fuel Fuji Carbureted (greenhulk.net)
    -My mechanic sync'd up all 3 carbs and even installed 3 extended hoses now mounted to the side and capped off in case it needed to be sync'd again

    3. What jets were installed?
    -I believe the ones that came with the Venom kit although I did keep all original parts that were replaced for a situation like this

    4. Was pop off pressure checked?
    -I believe so but I'm not sure how that's done

    5. Are the low idle speed adjustment screws good? Best way to achieve this is to leave the ski strapped to the trailer and back it in. Start the engine and get it up to normal temp. Adjust the idle speed screw to get 1100 RPM. Now turn the idle mixture screw (mounted low on the carb) in and out of the MAG cylinder to achieve highest RPM. Make 1/8 turn at a time and wait for the engine speed to correct itself. Adjust the idle speed screw to get back to 1100 RPM. Then do the same for the CEN cyl. Adjust the idle speed screw again to maintain 1100 RPM. Now do it for the PTO cyl. Doing this should get you the best/smoothest idle and take off.
    -Are the cylinders you listed in order from front to back or the other way around? Also how would I be able to check the RPM's of the motor without a gauge? Still pretty new to a lot of this so I'm learning as much as I can

    If you find turning the low idle mixture screws all the way in get best results, you have too big of low speed jets installed.

    If turning the screws out more than 2 full turns from a LIGHTLY seated position gets you the best results, you need a larger low speed jet installed.
    -I think he had mentioned something about them being around 2 turns from the lightly seated position. I sent him your entire response to get the precise answers for you tomorrow

    The hi speed adjustment screw (mounted high on the carbs) is for WOT tuning. When it comes to this, it's best to start out with too much fuel and take it away to achieve proper supply. So I'd suggesting starting at 2 full turns out from a lightly seated position and watch your RPMs and/or piston wash for proper fuel supply.
    -WOT tuning?


  7. #6
    https://www.amazon.com/dp/B079TD3HFP...roduct_details

    This is the kit I used to have all 3 carbs rebuilt

  8. #7
    Also I've been looking online and cant seem to find any genuine Mikuni rebuild kits. SBT has this one https://www.shopsbt.com/jetski/mikun...ki-yamaha.html but I can't tell if it would be compatible

  9. #8
    Click avatar for tech links/info K447's Avatar
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    Quote Originally Posted by Texan_Riot View Post
    Ö genuine Mikuni rebuild kits.
    www.Watcon.com has Polaris specific carburetor rebuilt kits using genuine Mikuni parts, and just the parts you need for a Polaris carb.

    Fuel pump kit is sold separately

  10. +1 by:


  11. #9
    Thank you! I'll order them today

  12. #10
    Quote Originally Posted by K447 View Post
    www.Watcon.com has Polaris specific carburetor rebuilt kits using genuine Mikuni parts, and just the parts you need for a Polaris carb.

    Fuel pump kit is sold separately
    I pulled up the 3 carb kit for Polaris skis but it looks like its just the diaphragm, jets, filters and springs. Although I guess I wouldn't need the gaskets replaced since they came in the Venom kit I already got

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