Mikuni pop off question

[RayFinkle]

Happy fourth all!

Was rebuilding the carbs for my 96 spx and I have a couple questions…I got the pop off set correctly but it seems like both needles slowly leaked over the course of ten mins or so and never held pressure. My carb kit didn’t come with a new needle and seat. Should I get new ones?

Also, on the pto side I didn’t have to plug the fuel return line to test the pop off…is this right? I feel like my return line is clogged somehow…

Thanks for the expertise!
Here are some photos of the carb

 

[AKnarrowback]

Pop off should be done with the carbs off the machine and disconnected from each other.

You should have to plug the return line to get the pop off test to work. Applying the pressure should be gradual and a test should be conducted "slowly". The second carb will have a smaller return orifice that is pretty small so make sure aren't applying pressure so fast that you aren't overpowering the outlets ability to vent.

If you are using wd-40 or trflo you should have a solid pop, slight drop in pressure and things should hold steady if you have a good needle and seat. I don't know if holding pressure fir ten minutes is necessary, I never let it sit for more than a minute. However, if you are doing a full carb rebuild the needle and seats should be included. Use ONLY GENUINE MIKUNI PARTS. The number fir the n&s is stamped into the seat, 1.5, 2.0 etc. Order two new ones just to eliminate any question because carbs are not "rebuilt" until all wear items have been replaced.

 

[POPPS]

And…I apply my pop off gauge to look for leaks at the needle and seat,,, and not to test the pop off,,,I will pressurize the entire carb before I disassemble it to look for leaks ,,,if the needle and seat are not leaking…the spring would have to be severely weakened for the pop off to change enough to affect throttle response,,,in most cases the culprit are the micro filters.

 

[RayFinkle]

Pop off should be done with the carbs off the machine and disconnected from each other.

You should have to plug the return line to get the pop off test to work. Applying the pressure should be gradual and a test should be conducted "slowly". The second carb will have a smaller return orifice that is pretty small so make sure aren't applying pressure so fast that you aren't overpowering the outlets ability to vent.

If you are using wd-40 or trflo you should have a solid pop, slight drop in pressure and things should hold steady if you have a good needle and seat. I don't know if holding pressure fir ten minutes is necessary, I never let it sit for more than a minute. However, if you are doing a full carb rebuild the needle and seats should be included. Use ONLY GENUINE MIKUNI PARTS. The number fir the n&s is stamped into the seat, 1.5, 2.0 etc. Order two new ones just to eliminate any question because carbs are not "rebuilt" until all wear items have been replaced.

Thanks for the reply, what’s confusing me is that on the PTO side I didn’t have to plug the return line to get it to pressurize.

 

[mikidymac]

Then your return orifice is plugged.

 

[RayFinkle]

Air goes through fine on this bottom nipple, top one doesn’t. Should that be like that?

 

[AKnarrowback]

View attachment 59449
Air goes through fine on this bottom nipple, top one doesn’t. Should that be like that?

No, air should go through the top one.

 

[JC-SUPERJET]

Your Orifice is plugged...