1999 Seadoo GTI 717 Mikuni Carb

[lmarkie74]

How can I tell if I have the original OEM Mikuni Carb for my 1999 Seadoo GTI 717. I have rebuilt this single carburetor and having problems with getting a crisp quick throttle response with the LOW side adjustment. I started with 1-1/2 turns (per starting specs) out with the RPM adjusted to 3,000 out of the water. Turning LOW screw in created a bog throttle. I ended up going the other way and am now out 2-1/2 turns and having a little improvement, but not greatly crisp, quick, throttle.

I went to "seadoosource.com/carbreference.html" and have noticed that the "Popoff" pressure is 36-40. The spring I have in their now is 23-43 (actually 23 psi). We all have experienced this before that on a 20+ year old jet ski, someone has been messing with something in it. For all I know, is the Carburetor could have been replaced sometime way back. 23-43 psi "popoff" is for Mikunis that have no accelerator pump. I do have the accelerator pump. Do you think I would have a better adjustment going to the 36-40 psi "popoff" pressure? Or is it possible to get this to adjust to my 717 motor?

 

[Grim]

I would suggest getting the original springs for your carb and resetting the POP off. When I rebuilt mine I had to get new springs and the POP off was right on target, not having any issues either. If you post a picture or your carbs , someone will be able to identify if they are the right ones.

 

[seadoom]

Use the spring that it calls for, verify that you using the the correct size needle and seat, verify jet sizes match specs, make sure the needle arm is not bent too far up/down per specifications (start with flush), after setting pop off make sure you also pressure test the needle/seat with carb together, set low and high speed to factory settings and make sure you are ONLY using genuine mikuni parts for as aftermarket kits can cause many issues.

 

[POPPS]

Seadom is spot on,,,go to the original OEM scenario...and diagnose from there.

 

[lmarkie74]

Use the spring that it calls for, verify that you using the the correct size needle and seat, verify jet sizes match specs, make sure the needle arm is not bent too far up/down per specifications (start with flush), after setting pop off make sure you also pressure test the needle/seat with carb together, set low and high speed to factory settings and make sure you are ONLY using genuine mikuni parts for as aftermarket kits can cause many issues.

I disassembled the BN40I-38 Carburetor again to verify what needle/seat and jet sizes. The the needle/seat is good (20), main jet is right (167.5) and the idle jet is not quite right what the chart says (70). Should be 75.

My old spring popped off at 23 psi. Spec for my carb should be 36-40. I replaced old spring with a longer spring in the Mikuni kit. Popoff is around 32 psi. I reinstalled the carb and turned it on the water hose. I am 1-3/4 turns out. Seems a little better, but the true story will be when I get it on the water.

 

[seadoom]

Still out of spec on the pilot jet and pop off, almost in spec is still not in spec and can cause issues. This should not be compensated by adjusting the low speed adjuster as that is only used for tuning the idle. Off idle to 1/4 throttle is pop off and low speed jet, both of which are still out of spec on yours. I would fix those and only run it completely in spec instead of chasing tuning issues as that is the only way you can really tell if there are other problems. Running on a hose doesn't tell you too much as there is no load on the motor like in the water.

https://www.seadoosource.com/carbadjust.html

If you finally get everything set to spec and you still have issues then you would be then checking things like verifying rest of fuel system, compression test, leak test motor for air leaks, etc.