787 Needle & Seat

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Hello everyone! I just became a member. So thank you for accepting me.

I just rebuilt the SBN 38 carbs in my '97 GTX with genuine Mikuni kits & N&S's Everything went together well. The pop off is right around 32 on each carb. All there other tests came out good except for the needle & seat pressure tests.

After pop off (using WD40), pressure will drop to 0 in about 30 or less on both carbs. When I try to test needle and seat pressure by pulling up pressure to 10-20 lbs, the same thing happens. They will not hold pressure but there are no bubbles coming from the needle or seat.

I thought that maybe my tester was leaking so I pinched off the hose between the carb and the tester and pressure held telling me there problem isn't with the tester.

Is there something I'm missing? Can pressure bleed off somewhere else in the circuit?

Any help is appreciated!
They will not hold pressure but there are no bubbles coming from the needle or seat.

Hard to say, it could be losing pressure elsewhere and not at the carbs. If the pop off goes off fine at 32 like you say and it doesn't bubble afterward it's likely fine. I did 2 sets of 787 carbs for my 2 skis, my pop offs were closer to 34-35 each time, and after the first pop off I'd sometimes I'd get the air bleed through the needle/seats, but I went with it anyway. I'm 3rd season on the 97' GTX and 2nd season on the 96' GSX. Both don't have any run or start issues.

But I'd make sure you use everything in the kits, including the orings for the HS and LS needles. Put a little lithium grease on the orings so they seat well.
If the needle and seat are not leaking that is good. Mix up some soapy water and use a small brush and paint the carb joints. You got an air leak somewhere. Good Luck !

ON a side note, I have 2 GTXs 1996.1997. I love the hull. I pulled the carbs off those skis4 or 5 times changing settings, adjusting different pop-opp pressure and checking performance. I find 36psi pop-off works best for our skis and our area.
Thanks for the feedback and sharing your experiences! I did use everything in the kit and double checked everything including checking for leaks with soap and water. Nothing showing up.

I just took it out for a run a couple of hours ago and it seems to be running decent. I need to do some fine running on the low speed idle screw but overall it runs much better than it did before. Had a bog that I couldn't adjust out before I rebuilt the carbs. Looked like the carbs hadn't been touched much since 1997 other than maybe a cleaning at some time.

Thanks again!
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