SBT Jetski Engines, Parts & Accessories

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  1. #1
    Joined
    Jan 2006
    From
    Cedar Rapids, IA
    Posts
    10

    Default New SBT motor...Engine bog. $25 paid for solution!

    Hello: I'll state my problem first: Engine starts up instantly. It runs great for just a couple of minutes. Good idle, good midrange and super good punch when WOT. But within 1-2 minutes it has power loss and can only be ran 1/2 throttle or engine bogs. It starts and idles fine, but continues to have more power loss till it won't get up on plane without stalling. Engine feels warm but I can still keep my foot in pisser water. Seems like a fuel delivery problem. Or ignition problem when hot...

    Now I will give you the background info. so you can best point me in the right direction. I will paypal one person $25 for the solution that fix's my problem. I am desperate to get this fixed before the 4th of July weekend.

    I installed a new SBT premium engine package for my 1993 Kawasaki 750ss, and installed the injector block off plate. Mixed the SBT break in oil with amoco ultimage gas. I rebuilt the single kehein carb with SBT carb kit, and installed new pump diaphrams after buying special non removable star bolt screwdriver...etc...

    New engine started within a minute. It appears to idle a bit rougher or have more vibration than last motor. Icreasing the engine idle rpm did smooth this out a bunch, but still appears to idle with more vibration than before. PTO to driveshaft alignment appears very straight.

    I rode 1/2 tank of fuel at 1/2 throttle on first outing. The next day out, I rode 1/2 to 3/4 throttle for the remainder of the fuel tank. No bog issues what so ever.

    3rd day out now using 40:1 mixture of amoco ultimate and yamaha semi synthetic premix. (I will switch to fully synthetic after 20 hours and rings have seated).

    When full throttle was applied ski didn't have the punch it used to. I adjusted the hi needle richer and bingo, the ski had more punch. It had a hesitation between low and hi so i played with the lo needle till I made it to rich and it bogged a bit down low... I screwed it back in until it ran good both down low and up high. I rode for a good 5 minutes and everything felt GREAT. That's when the bogging started.

    It started to bog and have trouble getting into higher speeds. I adjusted the jets in / out but could not overcome bog. After sitting for 5-10 minutes the jet ski initially pulls strong, but quickly bogs at 1/2 throttle or above.

    I brought it home and started from the gas tank to the sediment bowl, to the valve, to the fuel intake of carb. All lines free and clear. I removed and inspected the fuel pulse line. Pulled return line off and started engine.. fuel is returning to tank. I did find some sediment in the fuel pickup line on the ON unit, which I removed with air pressure. Jet ski bogs whether on ON or RES fuel selector. I also blew out the pickup unit on RES line. Both pickup units were plastic and about 2 inches long. Neither had screens on them. Both lines are made of steel and flow freely... Air blown into them comes out strong at the other end.

    Question... My sediment bowl is empty. Bone dry. Is this a problem? I also inspected check valve on top of gas tank to the upper vent line. no blockage, and when blowing and sucking, the check valve lets air in toward the tank, but not out or towards to the top vent... is this correct?

    I added an inline filter during engine swap between gas valve and carb intake. I can see fuel immediately fill up when engine starts. When I blip the throttle, I see a few bubbles in the clear filter, but filter remains full of gas. I use this same type and brand of filter on all my motorcycles with no problems. Do Jet skiis have a problem with fuel filters effecting flow? I could remove and splice line together with 1/4 " fitting...

    I have pulled plugs and they read a bit lean. I replaced and still engine bog. I have checked compression and have 150 and 148. I checked spark with a spark tool and both will throw spark a solid 1/2 inch...

    I removed carb and fully disassembled agian. Everything looks perfect, clean, all passages perfect. I am using longest or lightest spring on pop off valve and have adjusted the correct amout of gap. I do not have vacum tool to test pop off pressure. Could this be my problem? Why does it run fine till hot, then bog.

    The ski starts the second you touch the start button. It runs fine, and revs smoothly on trailer with water line hooked up. At the lake, it starts and idles fine in water. After a 1 minute warm up, it takes off with full power! Runs great. No hesitation. Smoothe transition low to high. Then I let off gas and turn around a couple hundred yards out... it has trouble getting back up to WOT... but runs good at 1/2 throttle... I get back to boat ramp... It is now bogging alot anytime over quarter throttle. If I give it WOT it dies. Starts and idles fine. Fuel starvation???

    Please help. How do I test further. How to I test coil, stator etc...

    Should I remove carb and intake and inspect reeds. They are original but had no gaps upon reinstall to new engine.

    Thanks a million for reading this long post. I am trying to give you all the info. to get the best advice. I have planned a huge 4th of July weekend at the lake and need the ski.

    Call or email me directly or post here if you can to help me out. I will Pay $25 bucks to the one who solves my problem!!!

    Tom Wirth
    319-551-3540
    wirth315@aol.com

    More info.

    Nothing is stuck in my impeller. I can remove the plugs and freely spin the pump shaft with my hand. Out of water I can blip the throttle and send water shooting out 10 feet.

    Could temp sensor be the culprit and can I bypass it for a lake test?

    One more note: When is driveway with water hose... engine runs, easily feels like it revs good with minimal throttle. Engine exhaust manifold never gets hot. I can keep my hand on it... In the water at the lake... this is very hot. I can keep my hand on it but it is hot.

    That's everything I can think of. Is this electrical or fuel??? Please help.

    Thanks

  2. #2
    Joined
    Jan 2006
    From
    Cedar Rapids, IA
    Posts
    10

    Default Re: New SBT motor...Engine bog. $25 paid for solution!

    Today I bypassed the heat sensor, bypassed the fuel valve and stripped 1/2" from plug wires and re-installed the caps into more wire. I will lake test this evening and give another post...

  3. #3
    Joined
    Mar 2003
    From
    SBT
    Posts
    21,545

    Default Re: New SBT motor...Engine bog. $25 paid for solution!

    No it's not your temp sensor, reeds, pop-off or engine.

    First, make sure your carb is adjusted to the stock specs. If it doesn't run correctly at those settings, you know you have something wrong witht eh fuel system.

    What you are describing simply sounds like running out of fuel.

    Yes the wrong or additional inline fuel filters can be a problem, the carbs don't have much suction and are ONLY designed for a low restriction fuel filter/water separator. Use the stock filter, that's it. If you see bubles - you have a leak. If you have a dry filter, you either have a leak or a stoppage.

    Put it back to stock and go from there. You may or may not have a carb problem, but until you get your fuel tank/lines straightneed out, you'll never know.
    SBT Tech Support is here to help with your problems.
    We try to answer each question quickly and accurately.
    Please do not use Private Messaging for Tech Support, use the forums.

  4. #4
    Joined
    Jan 2006
    From
    Cedar Rapids, IA
    Posts
    10

    Default Re: New SBT motor...Engine bog. $25 paid for solution!

    I lake tested last night with heat sensor bypassed and fuel selector bypassed. I was able to ride a full 5 minutes before bog came back. I then removed the inline filter and using a brass 1/4" fitting, spliced the line back together. It immediately ran better, and had more punch when going full throttle than the jet ski has EVER had. I hooked the temp sensor back up and it still ran good. Today, I will re-connect the fuel connector.

    When at top speed, the SBT motor is way faster than my old engnine. I have a big grin on my face as the old 1993 SST750 hull floats on the water. I actually have to slow down to turn so I know I'm pushing 40 plus mph.

    I spent 10 minutes fine tuning the stock carb settings. 3/4 to 1 turn out on slow needle, and 1 -1 1/2 on high needle. It got to dark to see the carb adjusters so I was not able to keep tuning. It has a hesitation in the mid range.

    When cruising for 5-10 seconds at 1/2 throttle and then going WOT, there is a 1-2 second hesitation or mild bog before the power then kicks in and it pulls hard. Then if I let off breifly and go WOT again, it's right there pullling hard... Out of the hole, it will pull hard, but if cruising at 1/2 throttle for a while, then to WOT, bog or hesitation.

    Being it's at 1/2 throttle and above, deos this typically sound like high speed needle being to rich or lean? I will adjust richer and see how it feels, and if it gets worse, I will go leaner.??

    Lastly, In my panic to get this ski running by next weekend I have 20 feet of Clear fuel line on its way, a new Keihin blue racing carb, pjs flo-stuffers, boysen reeds, a huge pile of Carb and reed gaskets from SBT and lastly, a new Solas KE-CD 11-16 impeller and bearing kit.

    I plan on installing all of it this week.

    Anyone have any experience with the 38mm blue racing carb? I don't have the carb yet but it looks identical to my carb. It has the same fittings etc...
    Thanks SBT for your post and I'm looking forward to hearing your thoughts on my mid range hesitation, and the new carb?

    Tom

  5. #5
    Joined
    Jan 2006
    From
    Cedar Rapids, IA
    Posts
    10

    Default Re: New SBT motor...Engine bog. $25 paid for solution!

    Please explain the sediment bowl to me. Mine is bone dry. The lines coming in/out are open and flow freely, but there is nothing in the bowl... How does this work as a fuel water seperator if no gas passes through it to let the water sink to the bottom? Do I need to prime the bowl with gas to get it started?

    Thanks,

    Tom

  6. #6
    Joined
    Mar 2003
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    SBT
    Posts
    21,545

    Default Re: New SBT motor...Engine bog. $25 paid for solution!

    Your bog is simply a mis tuned carb. Try going richer first, see if it improves.
    SBT Tech Support is here to help with your problems.
    We try to answer each question quickly and accurately.
    Please do not use Private Messaging for Tech Support, use the forums.

  7. #7
    Joined
    Mar 2003
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    SBT
    Posts
    21,545

    Default Re: New SBT motor...Engine bog. $25 paid for solution!

    The bowl should be full - if it's dry wither you have something plumbed incorrectly or something is leaking/stopped. Do you have all the lines in the stock locations with stock fittings?
    SBT Tech Support is here to help with your problems.
    We try to answer each question quickly and accurately.
    Please do not use Private Messaging for Tech Support, use the forums.

  8. #8
    Joined
    Jan 2006
    From
    Cedar Rapids, IA
    Posts
    10

    Default Re: New SBT motor...Engine bog. $25 paid for solution!

    Referring to page 72 of my clymers manual for the JH750SS, I have all lines plumbed perfectly, and have blown air in / out of all hoses to check for blockage.

    My sediement bowl is dry and always has been since I've owned the ski...?...

    The sediment bowl has two lines. IN and OUT

    The IN side of the sediment bowl goes to the vent up in the steering column, and the OUT side of the sediment bowl goes to the check valve fitting on top of the fuel tank pickup plate.

    The check valve on the fuel tank pickup plate let's air or liquid up or out of the tank but not back in. This line as shown in the cylmers manual goes to the OUT side of the sediment bowl, exactly how is is on my ski. Still no gas in sediment bowl.

    This check valve has an arrow pointing down towards the tank.

    Will it fill quickly at idle, or does it fill only when the ski is in the water and higher throttle applied.

    I don't see how the sediment bowl works the way it is designed without an IN and OUT to the gas tank...

    Should I buy a new check valve? I can blow in it and make it flow or check (stop)

    Thanks again, I appreciate the help.

    Tom

  9. #9
    Joined
    Mar 2003
    From
    SBT
    Posts
    21,545

    Default Re: New SBT motor...Engine bog. $25 paid for solution!

    LOL the filter goes between the tank and the swich, not on the check valve line :)

    www.buykawasaki.com has online microfiche - I susggest you take a look at the diagrams and put everything to stock...
    SBT Tech Support is here to help with your problems.
    We try to answer each question quickly and accurately.
    Please do not use Private Messaging for Tech Support, use the forums.

  10. #10
    Joined
    Jan 2006
    From
    Cedar Rapids, IA
    Posts
    10

    Default Re: New SBT motor...Engine bog. $25 paid for solution!

    Are you sure the sediment bowl filter goes between the tank / fuel selector switch. It makes sense to me... but why does micro fiche and clymers show the sediment bowl in / out going to the relief valve on top of the tank and to the vent under the handlebars...

    Clymers shop manual 1992-1994 page 72.

    Should I plumb the sediment bowl between the tank out to the sediment IN, and from Sediment out to the Gas on/off valve in?

    Then just run the gas tank plate vent or relief valve to up under the handlebars?

    I can try this to see if the sediment filter fills up...

    Thank you, I appreciate your efforts and help.

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