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  1. #1

    1200 non pv carb help

    hello, at work i have a yamaha ls2000 jet boat that is kicking my butt. boat came in with one engine blown up. shop that i work at we put an sbt reman engine in because we can't warranty an engine like sbt can for the price. nor can we rebuild one for the price either. keep in mind i am not a fan of sbt engines. but.... this isn't a discussion about the engine. both engines are fine now. when we install an engine we always go through the carbs to make sure they weren't the reason why the engine blew up in the first place. also check the fuel lines, filters, vent lines, and oil lines and fix/ repair/ replace as necessary. so carbs have been gone through, oil lines replaced, oil
    check valves/ filters cleaned, fuel fiters replaced, new manifold gasket, new carb plate to manifold gasket, new carb base gaskets.

    boat went to the water, engine was run and broken in with oil in the gas premixed along with running fat on the oil injection. no issues.now .......boat comes back and customer is complaining of bad vibration, rough idle, and having to give engines more throttle to keep them running. i check the plugs and notice a little rich but no problems. no metal or bad coloring. do a compression test and all is good. start the engines and notice very low idle thus the bad vibration. raise the idle engines smooth out then drop low and vibrate badly again. blip the throttle they come up then back down again and very rough idle. smells realy rich on the hose. so pull the airboxes and all 3 carbs on both engines dripping fuel out of the high speed booster ventury. on the carbs i went through and the carbs on the other engine that werent gone through. so all 6 dripping fuel out of the high speed at idle. so tried on the rear most # 3 carb the one i can get to without removing the entire rack, i open up the metering side and take a look. no trash or anything. change the needle but not the seat, put in a black spring to increase pop off pressure in case the fuel pump was blowing the needle open, replaced the metering block gasket, replaced the arm for the needle, and put it all back together and it still drips fuel out the high speed booster venturi at idle. im stuck! what else could it be? i checked my return line and itsw clear with no restriction. same for the vent line from the tank free and no restriction. even pulled the fuel return line from the carbs to the tank and it still dumps fuel out of the high speed venturi at idle. carb settings are set per sbt's carb settings listed online. keep in mind boat ran fine when it left with no drips out of the carbs, idled fine, and had top end 7000rpm like it should. now comes back with this problem i can't seem to point a finger at. maybe thinking all 6 needles and seats are bad, or the o ring around the seat may be bad. just need a little bit of help. any is appreciated. thanks, Steve mardell


  2. #2
    mudslanger's Avatar
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    The best advice i can give is to buy a pop off tester and pull the carbs and go through them.

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    or send them to bill.

  4. #4
    tested pop off pressure and its 55-60 psi with the stock spring from yamaha. carbs are stock 1.2 needles. o-rings were leaking around the seats replaced those put carbs back on and front and rear carbs stopped dripping fuel and center still leaks. looking at the tips of the needles there is a slight groove thinking this is the problem.

    probably going to change the needle and seats to a 1.5 and change the pop off pressure down to 30 psi or so.
    let me know what you think.

  5. #5
    I have no idea what bearing this would have on your problem...and you said you did a pop-off test but IF you bought the SBT carb rebuild kits, the O'rings for the fuel pump side are often crap! Out of 9 carb kits bought from them, all 9 leaked air at the base of the fuel pump side. I put back in the OEM O'rings and the leaking stopped immediately. SBT claims that they thought they got rid of all of the kits that had the problem. Guess not. Again, not sure if that could attribute to your issue.

    One thing I do know is that all of the 1200 non-PV engines that I have right now (2 of mine plus 1 for my bud's ski) shake, rattle and roll like crazy at idle. Tell your customer to get used to that because I don't think there is a work-around for it.

    Someone else will have to chime in on lowering the popoff by changing out the n/s but I thought that the reason for the high popoff on the 1200's was because of the excessive vibration of this motor? My limited understanding= 2 cents. Good luck to ya though.

  6. #6

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    Quote Originally Posted by slociviccoupe View Post
    tested pop off pressure and its 55-60 psi with the stock spring from yamaha. carbs are stock 1.2 needles. o-rings were leaking around the seats replaced those put carbs back on and front and rear carbs stopped dripping fuel and center still leaks. looking at the tips of the needles there is a slight groove thinking this is the problem.

    probably going to change the needle and seats to a 1.5 and change the pop off pressure down to 30 psi or so.
    let me know what you think.

    If you have the stock flame arrester, you do want the pop off to be arround 55psi to 65psi. some said it is fine at 45psi, but 30psi is too low for a stock flame arrestor. This is just my opnion.

    stock 1.2 is good too, y change it?

  7. #7
    Yamaha artisan Cutlass's Avatar
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  8. #8

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    Quote Originally Posted by Cutlass View Post
    Cutlass, what is dribbling?

  9. #9
    Yamaha artisan Cutlass's Avatar
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    leaking fluid

  10. #10

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    Quote Originally Posted by Cutlass View Post
    leaking fluid
    So how do you "see" it? I meant do i take off the frame arrestor and look into the carb?

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