Categories: Features

Skidmarks: Diagnosis Psychosis

There is nothing more hateful than bad advice.


Here’s the problem with deciding that one particular make and model of motorcycle is the only one you need for the rest of your life: they get old, develop problems, and at some point you’re pretty much on your own to figure out how to fix them. My 2001 Suzuki SV650 is the best motorcycle ever made, at least according to me, but that’s assuming it runs on both cylinders, which it currently doesn’t.

What is it about old motorcycles? Like cats, as soon as they hit the decade mark, they lose that like-new patina and start developing weird issues. Not only has my cat developed bad breath, he also feels the need to sit on my chest and yawn into my face at three a.m. Dude: if you’re nocturnal, why are you yawning? Similarly, my SV isn’t running right at high rpm, and the reason isn’t obvious. Like the cat, if my 16-year-old SV disappeared tomorrow, almost nobody would notice, but I’m going to try to fix it anyway.

It’s that most elusive of problems, the one disguised as no problem at all. The bike starts fine, idles cleanly, pulls okay and cruises along without a care in the world. But open the throttle to the stop in sixth, and it won’t pull redline, petering out well before the century mark (on a closed-circuit course, with a professional rider aboard, of course, and certainly not on a rainy Wednesday afternoon on the crowded I-580 freeway).

This exploded diagram of a Mikuni carburetor also doubles as‘s organizational flowchart, except Sean is the needle and Kevin is the clip (currently 2 grooves from the bottom). Evans is the pilot jet, and depending on day of the week, Tom is either the main jet or mixture screw.

If you want the gory details, here they are: it’s a 2001 SV650 with a full M4 exhaust system. There’s an EBC filter, the airbox snorkel has been removed, there are spacers under the tank to allow more airflow, and a 4% ignition advancer replaces the stock timing bolt. The carburetors, God bless their little constant-velocity souls, have been modified with a period-correct Factory Pro jet kit, with pilot jets, main jets and needles replaced and set to the recommended specs.

The problem is that the rear sparkplug – yes, just the rear plug – is fouling, dry fouling if that helps. At least I assume whatever is causing the plug to foul is the problem. After 30 years of riding motorcycles with varying degrees of shittiness and un-diagnosable conditions, I have finally learned to doubt that a totally obvious symptom is actually causing a problem. So this time, instead of trying to do things the old way, trying out free Internet advice until I give up, I’m going to try to methodically figure it out myself.

So far, I’ve discovered that the valves are likely in spec, and yes, the plugs are clean and gapped correctly, at least before my last test ride. They also deliver a fat spark when I test them on both coils. The fuel pump’s working because the front cylinder is running fine (I suppose), and would the bike even start or idle if the cam timing was off a tooth or an intake valve wasn’t fully closing? Everything obvious has been checked, so I’ll start with the not-so-obvious things the troubleshooting guide in the shop manual suggests (What? That’s not how we do things on the Internet!). I’ll swap out coils, the fuel pump, the black box, and yes, check the cam timing and valve clearance, as I haven’t yet spilled enough coolant on my shoes. At some point I will fix the problem or put the bike on Craigslist, hopefully attracting the attention of somebody with no desire to exceed 100 mph.

I have also learned, in my 20 years of swimming in the World Wide Web, to realistically value free advice. Because judging from what I discovered when I tried to search the Googles for other accounts of a similar problem, checking obvious and simple stuff is for suckers. Going up (or down) a heat range on the plug is popular advice, and it always solves the problem of plug fouling like magic, said no motorcycle owner ever in human history. Neither does moving needle clips, going up a jet size, balancing the carbs (carb sticks are a wonderful way to spray mercury into your eye, in case you need a good method for that), cutting a coil out of your carb slide spring, switching to flat slide racing carbs, getting high-output coils or even, as one forum wunderkind recommends, titanium emulsion tubes. I have no idea where to buy these, but I haven’t looked in a medical supply catalog yet.

Titanium emulsion tubes. You gotta get yourself some of these titanium emulsion tubes. They’ll fix ya right up.

When humans realize there’s no obvious solution for a problem, the crazies comes out in full force, leaping to the most tenuous and unlikely solutions. A bunch of ships and airplanes disappearing near Bermuda? Must be caused by aliens. Pyramids built by ancient people with no heavy machinery? Again, aliens. Donald Trump being elected president? Russians. Or aliens. Maybe even Russian space aliens.

When it comes to motorcycles, it’s no different. Within a few hours of this column posting, there will be some tasty examples of diagnostic overreaching. There may also be some good advice, but how to separate the wheat from the chaff? I know (now) to not grant credibility just because somebody sounds like they know what they’re talking about. If you don’t know what somebody’s talking about, it’s possible, even likely they don’t know what they’re talking about either. And if somebody tells you they know what they’re talking about because they’re an engineer of some kind, drop everything and run. Even engineers don’t listen to other engineers. If, however, he or she tells you they’re a software engineer, offer to sell them your motorcycle.

I wonder what medicine would be like if this sort of diagnostic science was applied to the human body. “Mr. Ets-Hokin, we’ve discovered a distinct heart murmur, and after going on the advice forum, I think the best course of action is to install the fuel pump from a ’63 Chevy Impala, because you need the extra flow.” Or maybe infrastructure projects? “My fellow citizens of the great state of California, to insure a steady supply of clean, reliable water for our children and future generations, we will replace our water system with a very long garden hose we bought on Amazon. Arizona tried it and said it worked great.”

“Okay, the guys on the WebMD discussion forum said this would burn off warts really quickly.”

Anyway, I better go. I have to buy a lathe so I can mill tungsten boots for my new 52mm flat-slide carbs I took off an ultralight airplane. Does anybody know how to upgrade my apartment’s circuit breakers? My blast furnace keeps tripping the fuses.

Gabe Ets-Hokin is an American medical researcher and virologist. He discovered and developed one of the first successful polio vaccines and plays jazz accordion with Paula Abdul’s pet llama, Sparky.

Note: This article holds the record for most carburetor jokes in a 1,000-word column.

Gabe Ets-Hokin

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Gabe Ets-Hokin
Tags: advicecarbsdiagnosticsgabe ets-hokinrepairskidmarks

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