A Phantom performance quandry

Today I had a phone chat with Alan from PowerSportsFactory. When he learned that my air filter was still attached to a portion of the original air filter system, he strongly recommended that I get rid of it and install the filter directly to the mouth of the carburetor. The configuration that has been working looks like this:




And since, due to the narrow confines of the motor mount and the tight fit of the hole that I already enlarged to fit the bigger manifold some months back, I was unable to fit the filter directly to the carb inlet, so I used a couple inches of the rubber tube from the original air intake. It looked like this:



Now here's the quandry. Alan told me that I would need to adjust the air mixture screw after removing the curved pipe. And I did that- by the book. It adjusted just beautifully and ran perfectly on the stand. Trouble is, it won't run worth a damm when under load! It just goes to crap! If I could get it out of the midrange and onto the main jet, it would begin to clear out and run fine. But through the mid-range, from just off idle to until it is running on the main jet, its unrideable!

Replacing the curved tube, and readjusting the air mixture got me right back to where I had been in the first place. And I tried adjusting the mixture 3 different times with test jaunts up my block, all unsuccessfully.

I'm stumped. I can not believe that bit of curved hose makes so much difference in the performance but I can't figure out which way to go with the carb and its jets and adjustments to get it running right. The hard part of course is that you can't get the poor performance when its sitting on the centerstand, the engine must be under load.

Maybe it needs a different sized pilot jet. I suppose bigger would be the way to go but that is just a guess. Any suggestions?

BTW, I did bypass the fuel shutoff with a new length of hose after replacing my curved inlet pipe and made one run up the hill successfully without the engine cutting out. I think that verifies that the valve is bad. I'll be awaiting the new one in the mail shortly. Thanks Alan!