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Old 01-29-2013, 06:32 AM   #101
toplessFC3Sman OP
Joined: Oct 2009
Oddometer: 68
Wow, another year gone by? I really need to get in gear & get this done! Anyway, some renewed progress now that the project car is frozen shut, and a friend at work has introduced me to what is basically a crowd-sourced workshop with welding equipment, mills & lathes, electronics lab, all sorts of stuff - i3Detroit, but anyway, this comes at a great time, since the biggest part of the bike holding me back right now is some welding that I need to do on the fuel rails, tank, and a couple fittings. After a lot of consideration and some mock-up, the general layout I'm planning on going with is this:

So the pump draws from the tank at the location for the stock carb feed valve (through a filter, which isn't shown here), and pressurizes the fuel. Now, instead of sending the pressurized fuel through both rails, in one end & out the other, the rails are on their own spur coming off of the high-pressure side of the fuel pressure regulator (FPR), with only an inlet. Plumbing it this way means that I'll need to make sure that the fuel lines running from the rails need to be continuously getting higher so that any air bubbles that get trapped can make their way up to the regulator to get purged. This shouldn't be a problem with the orientation of the throttle bodies, and by capping the other end of the rail, I'll have less tubing running around out near my legs where it could possibly get snagged, and would need fewer other fittings to complete the fuel system. The FPR will be mounted right underneath the tank so that it's higher than the rails, and can drain right back into the tank.

To get the FPR to work properly, I'm going to need to drain into the top of the tank, so that the fuel pressure doesn't change with the amount of gas in the tank, so to do that I'll need to weld a new fitting onto the bottom of the tank with a tube that sticks up near the top so that the fuel will always be flowing out above the fuel level. For the moment I'm just going to weld an NPT bung to the tank, and plan on using a compression fitting with the tube sticking far through it to accomplish this. I also need to weld another fitting on the tank for the outlet, since the stock outlet is stripped and in poor shape. Then I can worry about re-sealing it where the POR15 coating was flaking off.

The fuel pump itself has proven to be a bit of a problem, since I can't use an in-tank pump (which would simplify life substantially - except there isn't room). The smallest external pump I could find was a Walbro GSL393, which is 155 lpm flow, and will be drawing 5-6 amps where I'll be using it. The problem is that the fittings on the ends are M10x1.0 straight thread, and I've had a really hard time finding much that fits that on one side and ends in a compression tube fitting on the other. I could go to NPT or -6 AN in the middle, but then it becomes really bulky. Instead, I'm going to take the M10x1.0 threaded hose barbs that came with it, chop off the hose barb, and weld on a 90* compression fitting for a nice, compact adapter.

All of the various fittings & whatnot for the next stage have been ordered, and hopefully I can try to get it done later this week or early next week. In the mean time, I took a spare fuel rail and pressure regulator from the project RX-7 and hacked it up and threaded it to give me a nice block to screw in some compression fittings.

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