Well Jim, if you are satisfied with your responses, I am going to hijack your thread
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Do you have the part number for the Yamaha in-line check valves? Please share!!
Here is my story. I finally got my 3XV4 back together with a rebuilt engine. The previous owner was using premix but I put the pump and drive back on with some new intake boots that had the oil line spigots.
I filled the tank and bled the pump but did not prime the lines after the pump. My plan was to run premix until I have the injection system working properly. I have clear lines so I can see the oil flow. After running at or near idle for a while, the lower pump line (shorter to lower cylinder) filled up nicely and appears to be free of air. The upper cylinder longer line appears to be pumping but is not filling the line and not getting very far past the pump itself.
Do you suppose that my upper pump check valve could be the cause of this?
I will try and prime the line and maybe switch the two lines to see what might happen. It does seem line the inline valves might be a simple solution. As Jim said they work nice on my RG500 that had previously filled the crankcase with oil after sitting.
Thanks, Frank