Balance of power

Jacob Bronowski: speccy smart-arse, boyhood hero

If you’re a particular age and of a scientific/engineering bent you’ll certainly remember Jacob Bronowski’s much-lauded (and much-mocked) early-70s book and television series The Ascent of Man in which the learned but somewhat theatrical prof charted the development of humankind principally, in its technology.

All of which is a somewhat laboured introduction to what might cheerfully be called The Ascent of Manometer, the next stage in development once you have the technology: namely, a multi-cylinder motorcycle with more than one carb.

I know, I’m wittering. Essentially, if your machine has two or more carburettors, at some point you’ll need to balance ’em – in other words, set them up so they pass equal mixtures to their respective cylinders. How will you know when the carbs require balancing? The bike will have a lumpy and uneven tickover, unresponsive throttle, possibly overheating on one cylinder… in a word it’ll run badly! And if it’s running badly, sync’ing the carbs will improve the situation and provide a complete cure if that’s the core problem.

Spend money or plump for the Blue Peter approach?

To do it you’ll need an expensive vacuum gauge or a cheap(er) device called a manometer (detailed explanation here). Better yet, for a bike with two carbs you can homebrew a manometer  as easy as acquiring a length of plastic tubing and some ATF, brake fluid or similar. And what’s more it’s every bit as accurate.

Yes, really.

Anyone familiar with the carb’d Hinckley Bonnie and variants will know that the Keihin carb is a sensitive instrument which doesn't take kindly to time spent languishing in the garage – during a winter lay-up for example. For a (very) short while I owned a Hinckley Scrambler which, while an undoubtedly handsome bike and with a rorty exhaust note when fitted with TORs to rival any genuine or ‘reissue’ lookalike Brit machine, hated to sit for more than a few days and was, frankly, a big pain in the arse (I traded it for a far superior Harley 48).

Pretty bike Triumph, but no cigar…

The machine needed constant fettling and other than the front brake which was, frankly, shit, the twin Keihins were its weakest point.

Anyway, here’s what you’ll need: between four and six metres of plastic tubing with a 4mm bore and a litre or so of ATF (or your choice of brake fluid, old thinish oil or whatever you happen to have lying around). You might also require some kind of clamping to squeeze the tubes and lower the pressure drop reaching the fluid, but we’ll cross that bridge when we come to it.

Fold the tubing in half without kinking it to form a long loop. Hang it up somewhere with the open end uppermost and, using a funnel, pour in the ATF until you have around 0.75m in the tubing on each ‘side’ of the loop.

Loop the tubing without kinking it

You’ll find that a quantity of the fluid gets trapped at various points in the tube but if you leave it hanging for a while the fluid will settle at the lowest point. Ideally, you should mount the manometer on a rigid backing to facilitate ease-of-use. Mine’s attached to a surplus length of modular shelving bracket which, with cable ties through the brackets slots, is ideal for the job.

The finished instrument here mounted
on a length of shelving bracket

Now arrange your bike so that air can flow around the motor and the exhaust fumes escape (ie stand it outside or at the very least, open the garage/shed door). A large domestic fan pointed at the motor will help keep it cool.

Have a look at the carbs on your bike and familiarise yourself with the location of its vacuum nipples and adjustment screw(s). If there aren’t any nipples you’ll have to remove the balance pipe which joins the carbs and connect your tubing (possibly with some duct tape) instead. Check your workshop manual for details. The Keihins score in the balancing department with accessible nipples and only one balance screw.

I’m being deliberately vague at this point because your experience will almost certainly differ. However the nub of the process is essentially the same for all machines.

At the vacuum nipples, pry off the tightly-fitting rubber caps and attach the open ends of the tubing. Switch on the fan and start the bike. Immediately, you’ll see the fluid in the manometer zoom up one side or other of the loop. If it travels so quickly that it looks like reaching a carburettor, switch off the bike and clamp the tubing such that you reduce the draw on the fluid. You’ll probably find that the tubing must be squeezed until it’s almost flat and it might be a good idea to do this at the outset and release pressure as needed. Now you know why it’s best to have a good length of tube in the loop: it gives you time to react before the fluid reaches the motor.

A clamping arrangement to squeeze the tubes and reduce
the pressure is useful. Mine’s made from one of those
adjustable feet from an office desk and a piece of brass tubing

At idle, turn the balance screw slowly so the fluid begins to rise in one side (thereby falling in the other), reversing the screw where necessary to bring the fluid to roughly equal heights in the tubes (ie within a few mms is fine). Be gentle and turn the screw slowly and by tiny amounts.

When the carbs are balanced, stop the motor, remove the manometer and (very importantly) reinstate the rubber caps on the nipples. That’s it. Quick, dead easy and it cost you at most, a couple of quid.

Get you, just like a real mechanic! Gaffer a few well-thumbed nudes torn from Nuts on your garage wall and you’ll be that man my son.

Attending to Tomos #2: fabbing a carrier

Ever seen the secret stash chamber on a Tomos A3?

Hidden catch reveals ‘secret’ cache

Reach behind the saddle, tug on the catch and lift the seat to reveal it. Big enough for a flick knife, length of string, pet mouse, gum, porn mag, bong and all the other appurtenances a two-wheeled Tom Sawyer likes to carry around, not quite big enough for a helmet (unless you have the opposite of hydrocephalus), fuel can, or anything else even vaguely useful (that is, if you have no need to stab, tie up a parcel, grow an ear, chew, wank or huff).

Big enough for small stuff, too small for big stuff

The answer? A rack or carrier.

I have a welder, some scrap metal, a bench and an hour or two of free time – by an amazing coincidence, almost the exact ingredients for making one. Given I could’ve bought a factory example for six quid on eBay recently the exercise is admittedly pretty pointless, but I’m stingy, like making things and have an aversion to fattening eBay’s off-shore bank account so homebrew it is.

The remains of a school chair will soon become…

What I don’t have is a pipe-bender so a project such as this requires careful planning in order to use pre-existing bends or else cutting and welding to get the necessary shapes. Here’s an example of what I’m hoping to copy:

…a copy of this, the OE Tomos rack

First step is to cut out suitable lengths and cross pieces for the main part of the carrier. Next, is to turn ‘slugs’ on the lathe to strengthen the joints and provide something substantial to weld to. The alternative is to sleeve the joints but slugs have the advantage of being invisible once the welds are ground down.

Careful cutting and welding preserves the bends and obviates the need for a
pipe-bender. Now all I need to do is lay out the pieces on the bench, toddle off
to bed and wait for some hungry elves to come and make it into a rack

Turning solid steel ‘slugs’ to strengthen pipe joints

With the cross pieces shaped to match the diameter of the sides, the slugs turned and the various pieces held in place with a clamp I broke out the welder and set to. At least, I tried. No wire feed. Hmm. Nothing would persuade the wire to emerge from the torch.

My welder is a cheap(ish) Clarke 130EN Turbo which I use gasless with flux-cored 0.8mm or 0.9mm wire. Working back from the tip to the liner, everything seemed fine so time for a strip down and look-see. With the insides exposed I put a meter across the wire-feed motor which showed DC present. So far so good but other than ‘clicking’, it wouldn’t shift the wire.

Reflecting on the problem over a mug of coffee, it struck me there’s a gearbox fed by the motor which has (as you might guess) plastic pinions clotted with grease. Maybe the gears were seized? Though the whole shebang can be removed as a unit I thought I’d try a little heat first to soften the grease. Using an old hairdryer, I heated the gearbox and pulsed the torch trigger while twisting the speed pot to and fro. Half a minute or so of not very hopeful heating, pulsing and twisting and… success! It began to feed. Either the gears were gummed up, or there was dirt on the speed control track or something else equally minor yet devastatingly terminal. Anyway, here it was working again.

Unless it’s in the hands of a pro, a flux-cored gasless welder produces a strong but messy result. I’m no welder but I don’t mind ‘finessing’ the weld afterwards. However, and as is its wont, having sat for a while the flux-cored wire was blighted by moisture resulting in ugly, weak porous welds. You can counter this by maintaining a >3/4” wire length at the tip. Heat from the weld evaporates the moisture before it reaches the joint but it’s even harder to produce a tidy job.

However, welding difficulties aside, the rack began to come together:

Next morning…

…and the elves have done their work

I want to attach side guards as per the OE rack to keep a pannier from fouling the wheel, there’s some cleaning up to do and paint obviously, but pretty much the rack is together. I’ll post an update when it’s in paint and finished.

Now there's just this piece to weld in place, two brackets to make to
support the carrier behind the lamp cluster, a spruce up and some paint

Avoid pressed plates – paint your own

I like classic bikes. I don't like reproduction ('repop' in transatlantic-ese) pressed number plates. In fact, I loathe them. Whether restored and gleaming or rumpled, rusted and wonderful there's nothing that lets a bike down more than a quick squint at the rear showing up a repop pressed aluminium plate looking like a gold bonnet mascot on an invalid carriage. Ugly. Untoward. Unnecessary. Wrong.

Truly awful!

Obviously there were pressed plates in the 1950s and ’60s, probably in the ’30s and ’40s too, but for the most part, the 'classic' number plate was freehand (or possibly stencilled), white paint on a plain black sheet of ally or steel.

Much better! This is what we're aiming for…

Few cared what the number plate looked like. And no-one felt the need to waste their hard-earned on a plate that heralded its owner as someone with more cash than sense and an unhealthy obsession with pointless detail (that would be saved for readers of classic bike magazines published by Morton's). A registration plate was simply a necessary adjunct to a pleasurable life astride two-wheels. Something decreed by men in striped trousers somewhere in Whitehall. Necessary for the common good perhaps, not necessary for attention beyond being in place to put you on the right side of some curmudgeonly copper.

And the thing about painted plates is they age. Beautifully. The paint chips and fades, the plate, buckled, scratched and holed in places looks right. Take the time and trouble to restore a bike or maintain one in original condition and it's surely worth the small effort to recreate an original plate rather than toddling off to ebay for a pressed affair with all the charm of a fart at a funeral.

For bike enthusiasts with access to a computer (er, you) and a cheap printer (or a local library with free access) recreating the look of original plates is simple. Fire up a word processor, DTP package or any program with which you can manipulate text, type in your registration number and apply a suitable style. I use Arial Black at 164pt with appropriate leading and kerning tweaks.

Plate stencil using QuarkXPress

Print off a couple of copies. Take one and coat the rear with a thick layer from a stick of white chalk. Position your sheet of black enamelled steel or ally cut from an abandoned road sign or whatever on your bench, and cover it with the print-out, numbers up, chalk down. Fix in place with masking tape.

Now, with a sharp pencil, carefully trace the outlines of the letters with the pencil magically transferring the chalk onto the plate. When you're done, remove the print-out. No need for great delicacy, the chalk outline is pretty robust.

Time for paint. I find the best is Humbrol white enamel for a 'just registered' look, or white enamel with a hint of a Humbrol brown stirred in for a creamy, aged appearance. Experiment to find the look you prefer. Using a fine brush, paint in the letters and numbers taking special care not to go over the lines (the curves are trickiest). Set the plate aside to dry.

6x4 white on black, painted but not aged

You can age the plate further by putting it on the ground and dropping handfuls of pebbles and earth on it, wiping it over with an oily rag afterwards. Homebrewing your own plates in this way is quick, cheap, easy and satisfying and makes for a plate that's far better than anything you can buy.

If you want to make a black-on-yellow plate use the same method but find some yellow plastic for the plate rather than attempting to paint it – it's difficult to source the correct yellow hue. The 7x5 yellow plate shown below was made from plastic cut from a discarded Addis kitchen bin with plenty left over to make more plates.

7x5 black on yellow – better from a distance