that fuel restrictor could be very bad in a bypass EFI system like Polaris uses.
It is a cheap and effective trick on a dead-head EFI system like two-stroke cats use, with fuel pressure bypass on the pump in the tank. The was great cheap HP for F7s that were originally fueled to .80 lb/hphr and 128ish HP. This was pre-boondocker era, and we were searching for a way to drop top end fuel flow without hurting the already too-lean midrange. A smart engineer DTR subscriber emailed me suggesting that a tiny 290 main jet-size orifice in the EFI hose would accomplish that. I love being surrounded by smart people like that. But I couldn't believe that a 290 main jet-size orifice could feed an F7 engine. So on the dyno with a stock 128 HP F7 I started with a 1/4" ID orifice in the hose, which did nothing. Then I cautiously dropped restrictor size to .240 and still nothing. Maybe 15 restrictor changes later we were down to a 310 jet and fuel pressure finally began to drop, and power began to climb. On this sled we finalized the pressure at 37 psi on top end and HP was well over 144 HP at .60 lb/hphr. Other F7s that followed required 35-40psi to achieve the same top end fuel flow. That eventually led to D&D creating the adjustable PAC needle valve, and many iterations of the same idea from other companies. I used to sell dyno customers machined down needle jets for $20 they could install in their fuel lines and insert main jets into. But the problem there was the sled on my dyno was dandy at 37 psi, but if it got colder outside the injectors would stay open longer and drop rail pressure to 35 psi = deathly lean. So F7 savvy dyno tuned powerful sledders had to monitor their rail pressure with a dash-mounted gauge, and when temp dropped they had to go to larger main (or open the needle valve) to be powerfully safe. Sort of like reverting to carburetors. But for 140 plus HP no one complained!
But the Polaris bypass system doesn't allow for this sort of cheap trickery. That stock EFI pump blows its full capacity through the rail, then a pressure regulator on the opposite end of the rail bypasses anything not needed to create the desired rail pressure back to the tank. A tiny restrictor in the line coming from the pump creates a way-too touchy and possibly dangerous condition that might see top end pressure drop from, say, 56 psi to 49 psi but that could suddenly drop to 35 psi if temps dropped, way more than we might see with a dead-head system. Also, that might stack fuel pump head pressure to unsafe and fuel pump life-shortening levels.
The great and proven boondocker and now this new PCIII is the proper and safe way to set it and forget it (like the chicken-cooker guy Ron Popeil says), lean the sled out properly and not worry about watching rail pressure rise and drop with temp/ altitude.
