HMX - checking fuel pressure

Автор: RaymondLilly on воскресенье, 19 июля 2009 г. / Ярлыки: , , , , ,

shiny new fuel pressure gauge from Summit

So ever since I woke the HMX from its slumber this spring, it’s been bucking and popping when I stomp on the throttle. Unacceptable. I knew I needed to double-check my fuel pressure anyway, and I hypothesized that erratic fuel pressure was causing the bucking, so I ordered up a cheap Summit fuel pressure gauge.

ah, the threads don't match. Brilliant.

Unfortunately, when I went to mount it to my fuel rail, I discovered that the fuel rail has a flare fitting, while the gauge has a pipe thread fitting.

all this to adapt the gauge to the rail

So off to the hardware store I went. And, of course, I shouldn’t have expected to find a simple female-to-female pipe thread-to-flare, 90-degree elbow. Noooooooo. Instead, I needed a female-to-female pipe thread-to-pipe thread, a pipe thread 90-degree elbow, a male-to-male pipe thread-to-flare, and then a pair of flare nuts.

looking much more steampunky now

Used the flare nuts and a short length of tube to create a female-to-female flare adapter.

oh, yes, very steampunk

And with it all mocked up, it looks a bit ungainly, but it clears obstacles and provides an unobstructed view of my fuel pressure.

valve coring tool. Like an apple coring tool, but not

Next, I had to remove the Schrader valve from the fuel rail. The local bike shop sold me a core removal tool for a buck, and I placed it on the valve stem of an old bike inner tube for some leverage.

not a lot of pressure released. hmmmm...

Depressed the Scraeder valve to release the fuel rail pressure.

decored

Removed the core.

silvery adapters and gauge installed

Then installed the gauge and its adapters. Note that I painted the adapters silver to avoid leaving it looking like a steampunk’s wet dream. Fortunately, no leaks, and I was able to run a few tests with the engine running. Looks like it’s 3 psi below spec, and the fuel rail bleeds down immediately after shutdown, which it’s not supposed to do. Next up, I need to figure out how to read the pressure while it’s running and while it’s bucking to see if the fuel system’s the cause.

UPDATE (12.May 2009): McGean had a fuel pressure gauge on a hose that we clipped under the windshield wiper so we could monitor the pressure while driving. Recreated the stumble, and we saw no drop in pressure. So that probably means my ailment isn’t in the fuel pressure system, but in the ignition. Maybe I stabbed the distributor one tooth off? Wouldn’t hurt to stab it again, I suppose.



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