1995 Yamaha Wave Runner 3 Pop off pressure

[dalef62]

I am working on a 650 Yamaha wave runner 3, Mikuni carb has been rebuilt with Mikuni kit and I have a pop off pressure of 45#. Is that too high? The ski ran great before the rebuild and that is the pressure it had before the rebuild with the exception of a leaking O ring on the seat. Same spring was reused and has the same 45# pop off.
One problem the ski had and seams to still have is it will not start when cold, unless you give it a little premix in the airbox. As soon as it starts it is great! Then it will start till it is completely cold again without a problem.
Any ideas?

 

[Sportster-2001-951C-Stock]

If your original pop was 45psi then the air box might have a restrictive design and this is the normal factory calibration. Most cold engines will need some sort of enrichment, choke plates to create vacuum or perhaps a small mechanical primer pump to provide some enrichment.

If pop is too high, it takes a lot of vacuum to actuate the metering needle off it's seat and allow fuel to enter metering chamber. A cold engine cranking rather slowly might not create enough vacuum to pop the needle but one that's running on fuel produces more vacuum.

The diaphragm type carburetor is a vacuum operated "fuel on demand" system, in order to flow fuel into the metering chamber the diaphragm needs to see enough intake manifold vacuum to pull the diaphragm into the metering arm and lift the needle off it's seat.

Another possibility is the fuel pump check valves might not be sealing correctly or possibly the fuel pump isn't pumping well due to some kind of wear or improper assembly order? If the fuel pump doesn't move fuel like it should, the carbs will remain dry. Try an in-line primer bulb as a temporary test to eliminate this possibility.