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  1. #1

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    Ultra 150 carb help please

    Afternoon all!
    Could anybody help me with a couple of issues I'm having with my ultra carbs please? I can't quite find the info that I need when searching. The ski is running really quite flat off the bottom and through the midrange but the top seems OK. The engine has had a full rebuild and still runs the same as before (minus vibration from crank bearing) I'd like to know,

    A) How to split the carbs? do the fuel rails just pull apart? they seem really tight?!
    B) The correct procedure for checking the pop off pressure,
    C) Can the carburetter check valve operation be checked in anyway? They seem really full of oil and the ski is hard to start (More so after rebuild) If they are stuck open can anything be done and how??

    Sorry for all the questions but the ski hasn't had 'snap' or top end for a while (before and after rebuild) and it's driving me mad. I've chased everything back to the carbs, Full engine build, prop, pump bearing etc etc. I tried to rebuild them but the kits were Junk. The main vacuum diaphrams seem all good and intact but I haven't checked their full operation yet, I heard this can be done with compressed air on the bench?

    Thankyou.


  2. #2
    steve45's Avatar
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    Yes, the fuel rails just pull apart. You should change the O-rings. The same O-rings are used on the inlet valve seat and should be replaced also.

    Check for dirt in the fuel rails, especially the ends. Check for dirt everywhere.

    To check pop-off pressure, you'll have to apply pressure to the inlet fuel rail while blocking the return. You may have to make a fixture of some sort to do this. Pop-off pressure should be about 15 PSI. Sounds like the pop-off valves for the oil lines are sticking open. You may be able to free them by injecting some solvent into them.

    I finally plugged off the oil inlets on my carbs and installed Yamaha oil line valves. I drilled holes in the top portion of the carburetor and installed tubes to allow oil to flow into the top of the carb throat (the way Yamaha does).

  3. #3
    Use a shop vac to test the slides. Suck air through the carb with the butterfly open and the slide should open up and return to closed properly.

  4. #4

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    Thanks for the replies! I’ll give the shop vac a go raven, hadn’t thought of that! Steve45, I’m hoping a few go’s in the ultra sonic bath might free the check valves but if all else fails I’d love to know more on your oil set up? I’ve only had kawi’s and don’t know anyone with a yam to have a look at. Hopefully can sort it without going that route though. I’ll change all the O-rings as well. I’m suspecting the oil in the carbs or a dirty low speed circuit but The other thing is the TPS, could this cause similar symptoms? Do some people set it to WOT or is that just for modded motors? Mine is bone stock. Thanks!

  5. #5
    steve45's Avatar
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    I'll try to send you some info on the oil system when I get home tonight. I didn't take pictures, or I can't find them if I did, of the carb mod.

    You can see the part here: http://partsfinder.onlinemicrofiche....b=7&c=0&d=1998 GP 1200 W OIL PUMP, Item # 14. You need one per cylinder. I didn't want to pay the ridiculous price for new ones, so I was able to scrounge up some used ones from various people here that had removed oil injection systems. Test the valves first. They are called check valves, but they are really pop-off valves, designed to open at a specific pressure (about 4-5 PSI). Make sure the arrow is pointing toward the carburetor. Secure them with stainless steel safety wire.

    The nice thing about the Yamaha set up is that the cylinder still gets oil if the carb gets plugged up. It can save a cylinder.

    I've never had trouble with the TPS (yet).

    EDIT: Sorry, I can't find any pictures of the mod I did.
    Last edited by steve45; 03-14-2019 at 09:29 PM.

  6. #6

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    Managed to test the valves using a step down on the pop off gauge, looks like two are working and 1 is stuck open, fingers crossed I can free it up. Tried the vac on the diaphrams as well, they all open but only halfway? Just up to the throttle plates but I assume it’s because I cant get a proper seal over the inlet.
    Managed to split them as well and the fuel rail O rings look pretty scruffy so that’s something as well.
    Next step is stripping them and getting them spotless!

  7. #7

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    Well I'm at my wits end with these carbs. I can't find the correct O rings for the fuel rails and seats anywhere, 7mm x 1mm are too small, 7mm x 1.5mm are too big. The ones that came with the Junk rebuild kits I bought are too big for the rails. (I've literally been able to use NOTHING from the kits due to p**s poor quality) Kawasaki want 3.50 each for them and I need 19. Ridiculous. Oil? Can anyone post a link to the correct O-rings????

    Also is there really nothing that can be done with these pop off valves in the carb other than convert to yamaha ones? Thanks!

  8. #8
    steve45's Avatar
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    PM sent about the O-rings. As far as the pop-off valves, you may be able to clean them by flushing with solvent and hitting with pulsing air pressure. It takes very little pressure to open the valves, 5 PSI. Hit them from both sides of the valve. If that doesn't work, at least the Yamaha valves are available (but ridiculously expensive!).

    Sounds like you're paying twice what we are for O-rings.

  9. #9

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    Thanks Steve I'll check my PM's! I've miscalculated on the O rings somehow, They're 2 each I've just checked, I'd seen them on Ebay i think for 3.50.

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