Of Clutches and Carburetors

Behold the vacuum tubes of motorcycles. Enjoy ‘em while you got ‘em.

Originally published in BMW Owners News.

According to the BMW airhead cognoscenti, one should synchronize Bing carburetors using one of the following methods:

• Vacuum gauges (preferably without exposing oneself to a deadly reservoir of mercury).
• Shorting out one spark plug with a long screwdriver, taking care to avoid the 12,000 volts coursing within inches of your fingertips.
• Listening carefully while twisting the throttle with one ear next to the sputtering engine.

Or, in my case, you could use the method that supersedes all these: dumb luck.  

This may include the burning of incense, performing ablutions, or genuflecting before a lifesize image of Hans Muth. To accentuate the suffering, this should be done in an unheated garage, wearing only a T-shirt emblazoned with a BMW rondel.

I have worshipped at the altars of Parkhouse, Plam, Porter, and Snowbum. I have served a long apprenticeship and killed innumerable brain cells in search of elusive gas leaks and perfect jetting. Alas, I am no wiser.

Will the youth of tomorrow ever know the agony and ecstasy of these explorations? No! Will they care? Of course not. Nor should they.

Carburetors, like clutches and cables, have become the earmarks of antiquity. There will come a time, in the not-too-distant future, when exactly no one will know how to adjust or service these devices. Carbs and clutches will seem as weird as a wall jack. That sensitivity in your left hand, developed over 50 years of riding, will be as redundant as knowing how to use the cue lever on your phonograph or send a fax.  

Carbs and clutches, though we love them, are the vacuum tubes of motorcycles. Enjoy ‘em while you got ‘em.

The Many Mysteries of the “Instrument”

To know the inner workings of the “instrument,” as carburetors are fondly called in Great Britain, is a kind of secret handshake among enthusiasts of a certain age. By my count, a Bing CV carb like that on my 1978 R100/7, contains about 30 parts, many of them the size of a fingernail, or a grain of rice. Some of these contain tiny passages that become clogged with stale gas, which turns to varnish, which in turns causes rough running, or no running at all, and leads to histrionics and much self-flagellation on the part of the long-suffering owner.

Bill Plam, of Boxer2Valve, has a wonderful video on how to completely refurbish a Bing carburetor. Though he makes it seem easy, when the parts are laid out on the bench, it looks like someone set off an explosive device in the nut-and-bolt aisle of the local hardware store. Spreading out the parts in this way implies great knowledge, even when none exists, as in my case. When one of my motorcycles is in this state, I always make a point of inviting a riding buddy over, if only to impress them with my command of the impossible.

What could possibly go wrong? Because I own four vintage motorcycles in addition to my 2016 BMW R1200 GS, my life is a series of gas leaks, float bowl explorations, jetting experiments, cable adjustments, and needle height changes. The fact that all these motorcycles are stored in a garage that contains our furnace and pilot light makes life that much more exciting. If you see a great conflagration from the general direction of northern California, it’s probably my house. Do me a favor and call the authorities, as I may or may not be conscious.

My most recent conundrum was to solve a gas leak and synch the carbs on my 1975 Honda CB400F—you know, the cute little café racer with the sexy four-into-one pipes. I removed the bank of carburetors four times in succession, amidst much sweating and profanity, in search of the problem. The eventual solution involved an inexplicable mix of new OE parts, old parts, and aftermarket imitations. It runs flawlessly, though I really have no idea how I accomplished this.

Will the youth of tomorrow ever know the joys of this Ouija board approach to motorcycle repair? Of course not. There is no mystery or guesswork to today’s bikes, just a GS-911 diagnostic tool and a laptop. Carburetor repair is a form of exquisite pain that future generations of motorcyclists will never know. And probably, never miss.

Friction Affliction

As with carburetors, the signs are all around that the conventional, lever-actuated clutch is going the way of the wall phone. BMW, Honda, Yamaha, and others are all offering bikes with automated clutches. Some, perhaps in deference to the dotage of riders like you and me, offer the interim solution of shifting with no clutch lever. Others dispense with shifting altogether. Just twist and go.

I have to confess: I understand the attraction. I taught motorcycle safety for many years, and a large percentage of our time was spent instructing folks how to use a clutch. The first question was almost always: “What is a clutch?” To the youth of today, you might as well be describing how to use a push mower.   

Once, trying to evoke the poetic aspect of clutch use, I said that there was “artistry” in the use of the left lever; that it represents one of the joys of motorcycling; and that its proper use denotes great experience and erudition. Indeed, I continued, waxing eloquent, there is nothing quite like a smooth downshift, accompanied by a deft blip of the throttle, prior to arcing into a corner. Or the ineffable joy of pre-loading the shift lever and feeling the cogs snick into place.

The students listened patiently to my thesis, considering each point in turn, and said: “Huh?”

(I imagine later, at the coffee shop, the students are saying: “Can you believe that guy? What’s all this about the ‘artistry’ of the clutch? Maybe he should go home, cue up a few cassettes on the ol’ boom box, and lie down for a while.”)

But hey, I get it. The youth of today wants to twist and go. And why shouldn’t they? After all, motorcycling is about forward propulsion, not epiphany.

In the future, no one will know, or care, that the exposed portion of an airhead clutch cable should measure exactly 201 mm, or that its junction with the lever arm should be precisely 90 degrees for maximum leverage and ease of movement. Nor will they know the myriad wonders of pressure plates, friction plates, or the beauty of the snowflake-shaped diaphragm spring.    

When these ancient artifacts are gone, something will have been gained, in the realms of convenience and ease of operation. But something, of course, will have been lost.

Alas, it’s no longer my business to resist these changes. I’ve been fanning the damn left lever since I was 11 years old, and I don’t plan to give it up anytime soon. Nor will I be foregoing my carb stix with their deadly reservoir of mercury, or the myriad wonders that reside in a float bowl.

Thankfully, I’m secure in my dotage. If you need me, I’ll be home, short glass in hand, listening to my phonograph and reading Cycle World, circa 1976. With Koss headphones. They’ve got a cord, so watch your step.