Fuel system planning

OK, so today I completely changed gears and didn’t do any more ignition-related work – instead I got to playing around with fuel-related stuff. Ever since I received the engine, I’ve been bothered by the routing of the supply line to the throttle body. This line goes from the mechanical pump at the back left of the engine, and just sort of hangs underneath the sump on its way forward. That’s not great because…that’s where the exhaust will be.

This was one thing I was interested in while looking at RVs at Oshkosh. One I saw with the cowl off had a pretty obvious solution – just route the line around one side of the engine, above the intake runners. But that plane had a different fuel injection setup from mine, so it still required some thinking on my part. That setup had the throttle body inlet on the middle left side, whereas mine is low on the right side. That’d make for some interesting routing to get the line up above the intake runners.

However, while looking over documentation on my injection setup, I found an example photo that showed a really simple solution. The throttle body doesn’t have to be oriented any particular way, and in this example photo it was rotated 90° from my orientation. This moves the fuel inlet to be high on the right side. A quick test run of this setup showed that it makes for great positioning of the inlet – the hose is at the perfect level to route around the right side above the runners:

An additional benefit is that after moving the throttle arm to the opposite side of the body, both it and the mixture arm are in a great position to mate with the control cables, which can come right underneath the oil sump:

And at the back of the engine, the hose has plenty of room, as well as plenty of spots to secure it along the way:

The only thing that was going to be odd about this was connecting the hose to the mechanical pump. This came with 45° fittings on both the inlet and outlet side, which weren’t ideal for my new arrangement. But I figured that’d be easy to solve, I could just find the right 90° replacement fitting. Fortunately, before I added that to my shopping list, I went to go looking through the FWF kit to see what hoses were in there – mainly I was thinking of the feed hose from the throttle body to the flow divider on top of the engine. Turns out there are already two of the 90° fittings I need in there. I should probably look in that kit more often, this surely isn’t the last challenge I’ll try to puzzle out on my own unnecessarily.

The one thing I haven’t decided yet is whether I want to get a new supply hose. The one I have is the right length, but would need another 90° adapter on the fuel pump end. This would be easy enough to get, but I’m kind of wondering if it would be better to get a new hose with 90° fittings on each end. This way, I could eliminate two adapters, both of which are additional potential leak points. The downside of this approach is that a new hose is…let’s just say quite a bit more expensive than an adapter. Then again, I could probably resell the hose I have now and recoup some money.

Anyway, that’s where I’m at today. I’m holding off on my Spruce order for the time being; I want to look at my firewall component mounting and see if I may need some additional hardware for those items. It’d be nice to get as much stuff on hand as possible, so I can roll with the momentum I’m feeling right now. Mounting everything on the firewall means I can be free to re-hang the engine when I’m ready, which will in turn allow me to start working on really fun stuff like control cables, engine sensor wiring, and so on.

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