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The tinker’s work is never done

February 21, 2008

Riding on Fairview, on the way home from Queenie’s Sunday ride, the exhaust note increases in volume by at least two orders of magnitude. Aw, man!

I really don’t need a major component failure now. Luckily, I’m in a good spot; I can pull into the parking lot between the various yuppie bistros on Lake Union.

I pull onto a side street and get on my hands and knees. Oh. The exhaust pipe has popped off the exhaust port. I guess it wasn’t tight enough… a racing engine is usually the result of an air leak, which would be the case if the pipe is loose. It’s not a good idea to ride it without the pipe attached. The exhaust is really hot, which could damage the floorboard or other parts of the bike, and the engine actually needs the back pressure the pipe provides to run properly. Plus you could get a ticket for excessive noise.

There’s nothing to be done until the pipe cools off (unless, of course, you like 3rd-degree burns on your hands), and I rather stupidly left the tool pouch at home. I can go home, get the tools, and by the time I get back should be able to safely deal with this. There’s a space at the curb behind a Nissan Altima, so I wheel the PX over and park it.

I can even take the SLUT part of the way!

It had just finished its outbound trip, so it needed to go past the Fred Hutch stop and do the weave to get on the inbound track. Just a short walk, and I’m on board. With one other person.

Oooh, this thing is going much faster than on opening day. The operators have had a couple months’ experience, and have probably figured out just how much swept area the brakes have. And most likely, the streetcars’ software can modulate throttle and brake inputs so there’s less of a jolt.

Hopping off at South Lake Union Park puts you close to the bus stop at the 76 station at Westlake and Mercer. From there, I should be able to catch a 17 home. I got a 74 instead, and the driver not only let me off next to the Fremont Bridge, she gave me a transfer good until 8:00 pm. Score!

It was dark by the time I got back, and the pipe was ice cold. I’d brought the 3-lb. hammer and a 2×4, but they weren’t necessary. I was able to swivel it on the 17mm bolt and slip it tight onto the exhaust port. While you want to be careful not to make either circle an oval, you can reef on the collar bolt. Just a bit.

The next day, I’m riding to Madison Park and the engine is barely able to idle. I get to Madison Park and pop the cowl, twiddling the idle adjustment screw (the one that sticks up through the air cleaner cover). Nothing. After a minute, it won’t idle at all, no matter where I twirl it.

I looked over Doc’s shoulder when he disassembled the Frankenstella’s carburetor, so I’m feeling pretty confident about diagnosing this problem. I’ll get right on it, after I finish my coffee!

I have to keep hitting the starter, and shifting gears has the engine feeling really coarse or about to stall. This is troubling.

First thing to do is check the idle jet. It’s the smaller one of the two brass circles next to the carburetor throat. If it’s dirty, or damaged, the engine will idle poorly, if at all.

It looks fine. No clogs, no damage. I have not touched the idle mixture screw on the back of the carburetor, ever. And it’s darn near buried in a clump of ooky schmutz, so it’s safe to assume that’s not the problem.

No, the problem becomes abundantly clear when I pull out the main jet assembly.

Air corrector, mix tube, main jet

There was only an air corrector jet and a mixer tube. The main jet was still down in the hole. It had detached from the mixer tube.

My bad. The original 98 main jet was a super-tight press fit; the new 100 stuck, but could be pulled out easily with fingers. When I installed it, I thought it’d be okay.

There’s raw gasoline all over the carburetor. The engine ran okay, but would often stall when warm. I just figured it was something like heat soak.

I fished it out by taking a small Allen wrench and sticking it down in the jet, then using it like a lever to hold it against the wall of the hole as it comes up.

As I said, a main jet needs to be a really tight press fit in the mixer tube. If it isn’t, the part that goes into the mixer tube has two spaces separating the halves of the flange. You can stick a screwdriver gently into the spaces to push the flange halves out. Be careful; push a bit, fit the jet. Still loose? Take it out, push a bit more. Repeat until the jet is a tight press fit.

If the carb is really dirty, squirt some carburetor cleaner on the dirty spots. Do not use anything but carburetor cleaner, even on the linkages. WD-40 or whatever will leave a residue that attracts dirt.

I realized something else. The grommet that slips over the idle adjustment screw should be pressed into the underside of the air cleaner cover. A tight seal is needed, so the only air going to the carburetor is what comes through the bellows (which gets the air from the hole in the frame under the front of the seat). Previously, it wasn’t.

I throw everything together and twirl the idle adjustment screw three turns out from fully tight, where I’d left it in Madison Park.

A brain cell fired, saying “check the spark plug!” It was wet with gasoline. I’d installed this one not at all long ago, so I’ll clean it and save it. Since I save the ones I remove, I took the one the new one replaced and put it back. It’ll do for now.

The engine fires right up and settles into a fast idle. Not racing, but fast, as if there were an automatic choke. I twirl the idle adjustment screw to the left until the engine sputters, then back to the right a skosh.

Time for a test ride. Favicon

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One Comment
  1. February 21, 2008 7:46 am

    Ah yes the joys of riding a classic. “Fixing your bike in exotic places…” When people ask about the Bonneville’s year of manufacture I say “2007, no vibrations no leaks and starts every time.” These are the good old days!

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