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Pipe Dreams: the epilogue, part 2

August 9, 2007

Heading south on 15th, I crank the right handgrip hard, but not all the way. A glance at the speedometer reveals it’s pointing at 60. Sixty! And there’s a whole lot more throttle left.

By Jove, I think we’ve got it. I quickly realized the 112 jet was way too rich. The spark plug not only never got a color, it smelled strongly of gasoline. At wide open throttle, you could feel how loaded-up the engine was… and it was pretty much done at 55 (47) mph. In fact, when I used an old plug for a few miles, the carbonization around the edges had actually been washed off. Maybe the decarbonisation outlined in the Haynes manual had been taken care of.

Brandon at Big People had suggested changing the air corrector jet and mixing tube (see the picture below) as well as the jet. Stock, it had a 150 air corrector, a BE-5 mixing tube and a 98 main jet. Try a 160, a BE-3 and a 103, he said.

The jet assembly for a PX 150’s stock carburetor

Out on the road with this setup, the PX definitely feels peppier, especially at higher speeds and wider throttle openings. However, it has a serious hesitation on initial throttle tip-in. Oooh, not good… most of my riding is in city traffic, and being able to dash away from a light or a 4-way stop is critical.

I have enough parts now, let’s try the 103 main jet with the 150 air corrector and BE-5 mixing tube.

Okay, it fires right up (well, the engine was warm). Out on the road, no hesitation and noticably stronger acceleration in all gears. Let’s try some things!

Up the hill on the west end of the Magnolia Bridge, while it’s struggling a bit I can hold 4th gear (stock, it ran out of breath in 3rd at the top of the hill). Going east approaching the low-level West Seattle Bridge, a rusted-out ’86 Geo Prizm with one of Mr. Toothy’s relatives comes after me, but I crank the throttle hard an zoom away strongly, even though I’m in 4th.

This morning, I went all the way up Fremont Avenue to 46th in 4th gear, and was even able to recover without downshifting after a minivan briefly stopped ahead of me for no apparent reason. I’ll look at the plug later, but unless it’s a seriously wrong color, at this point I’m willing to call it good.

There might be a chance for a top speed run this weekend. Stay tuned. Favicon

  1. August 9, 2007 10:12 am

    Remember, the speedo is eight mph fast, so 60 indicated is 52. Still five mph faster than before!

  2. August 9, 2007 4:21 pm

    I know Fremont to 46th, and pulling in 4th gear is impressive. It sounds like you’re getting her dialed in quite nicely.

    Have fun,

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