A Few Random Tech Tips...

Over the years I have made enough mistakes -- large and small -- in the garage while working on my bikes. So I'll share a few tips here in the interests of lessening your pain -- after all, life is too short to learn everything the hard way. From time to time I'll add new tips as they occur to me. But here are a few to get you started:

Idle (Pilot) mixture setting

Ever tried setting the idle mixture on your GS1000? If you've got the original VM28 (for the 1979 SN) or the VM30 (1980 ST) carbies, you'll know you're in for a rollicking good time: fuel screws, combined with air screws, make for so much fiddling and fuddling that you're bound to go bonkers long before you get it right!

And the solution? The mighty 'Gunson Colortune' plug. Essentially, it's a spark plug with the insulator made of transparent glass, so that you can actually SEE the colour of the combustion flame. Yellow = too rich, but if you turn the fuel screw inwards until the combustion flame colour just turns blue, you're spot on! It makes tuning your idle mixture for each carburettor/cylinder an absolute doddle, and totally takes out the guesswork. One of the world's most under-rated tuning tools, I reckon.

They're readily available on eBay, and if you like go and buy one; it will be money very well spent. Although please note: for some funny reason, folks on the GS Resources forum report that it doesn't work with CV (diaphragm-operated) carbs. I can vouch for this: I was able to tune the VM carbies on my GS1000S without a hitch, but with the CV carbs on my GSX1100SZ Katana all I could see was a yellow combustion flame, no matter where I turned the fuel screws. Dunno what's going on there, but that's the way it is.

But if you're feeling game, you can always make your own 'colortune' plug -- which is what I did, after seeing how elementary the Gunson item is.

DISCLAIMER: all of what follows, is what I did. I am not recommending or advising in any way. If you make your own 'colortune' plug, and it doesn't work, or it blows up, or you are careless and injure yourself in the process, or WHATEVER... IT'S YOUR FAULT. Got it?

Anyway, here's a finished item which I made myself:

How did I do it? Right then, here's the method:
  1. Get an old spark plug, and remove all the porcelain and the centre electrode. **MAKE SURE YOU ARE WEARING SAFETY GLASSES, AS A FLYING PORCELAIN CHIP COULD VERY EASILY RUIN AN EYEBALL!** This is actually the hardest part of the procedure, so TAKE YOUR TIME and BE PATIENT, and take it out bit by bit. A hammer, a vice, and range of small screwdrivers used as chisels should eventually do the trick. They did for me, anyhow.
  2. Get a piece of strong wire, nice and straight, approx. 2mm thick, which you will use for your new centre electrode. It should be about 5-6" long.
  3. Sharpen one end of the wire, so that it will...
  4. ... neatly poke through the sticky-tape which you will put over the top-end of the old spark plug body.
  5. Insert the sharpened end of the electrode through bottom-end of the plug, and gently push it through the tape that you have stuck over the top end of the spark plug body.
  6. Push it inwards until the bottom end of the electrode is some 5mm (or so) past the lower edge of the spark plug body, thus:

  7. Then, with the assembly upside-down, pour some 5-minute 'Araldite' or other clear epoxy glue into the lower (open) end of the spark plug body. What will stop it pouring out the other side? The sticky-tape, of course. *Take care* that you don't trap any bubbles of air in the epoxy; gently pushing the epoxy down into the plug body with a piece of wire should help coax any bubbles and air pockets to the top.
  8. Let it set over the next hour or so; we want the glue nice and solid before we perform the finishing steps.
  9. Using a thin pick or scribing implement, remove any epoxy glue from the electrode end and the inside of the plug body... we do want the spark to make it across the gap, you know.
  10. Pull the tape away from the top end of the spark plug body, and slide it off the end of the electrode.
  11. Now get some heat-shrink insulating stuff, and slide it over the top end of the electrode, except for the uppermost 10mm or so. Using a hair dryer or small blowtorch, shrink the stuff onto the electrode. Do three layers of this wondrous stuff, just to be sure that you're not going to accidentally zap yourself while using the plug. Make sure that the heatshrink tubing goes all the way to the surface of the epoxy at the top side of the spark plug body.
  12. Then, mix up a little more epoxy glue, and put it around the base of the heatshrink insulation, on the top of the spark plug body. This will help make sure that (i) the heatshrink tubing stays put, and (ii) that no sparks can arc across outside the plug, instead of inside (which is where we want the action to happen, eh).
  13. Finally, what I did was solder some 4mm OD copper tube to the top of the electrode, so that I could then cut a thread using an M4 x 0.7 die, to screw on a conventional spark plug tip if needed.
  14. And now, your very own 'colortune' plug is ready for action!

And here's a schematic diagram of what the 'colortune' plug will look like in cross-section:

Once constructed (or bought from the legendary Gunson crew themselves), the 'colortune' plug is so easy to use:
  1. Insert the plug into the cylinder for which you want to adjust the idle (pilot) mixture, and tighten lightly.
  2. Push the spark plug cap onto the top of the 'colortune' plug.
  3. Start the bike and warm it up.
  4. Turn the fuel mixture screw outwards (ie. richening the mixture) until the flame colour being displayed through the transparent (epoxy) part of the plug is yellow (if it isn't already).
  5. Then SLOWLY turn it inwards (making the mixture leaner) until the combustion colour just turns blue. And, that's it -- the idle (pilot) mixture for that cylinder is now spot-on.
  6. Repeat for each of the other cylinders/carburettors, and you're done!
Then you can get on with tuning the mid-range (= needle height) and top-end (= main jet size) of the fuel mixture, using the tried and true 'ass-dyno' which every motorcyclist possesses.

Fuel filters & fuel line routing

Some years ago I had a lovely black GPz900. The only snag was, after a while it developed a mysterious problem. Like, you'd be bowling along the highway for 50kms (30 miles) or so, and it would start missing, spluttering, and then conk out. You'd pull over, thumb the starter button, and nothing. After 5 minutes or so you'd have been poking around the bike, and you'd thumb the button again, and she'd start up without a problem! So you'd ride another 50kms, and the same thing would happen all over again.

I tried everything I knew: cleaning the plugs, draining the fuel bowls, looking for electrical gremlins -- but all to no avail. In exasperation I rang my local Kawasaki dealer.

"Hmm," he said, "is your bike a black one?"

"Err.. yes!?" I replied.

"And have you recently put in a fuel filter?"

"Well... yes!" I stuttered -- wondering if this man had ESP powers or something spooky.

"Well, throw away that fuel filter!" His explanation was that if you have a fuel filter installed, then it will inevitably trap a bubble of air -- and with things getting hotter than average under the black bodywork, the bubble will expand in the heat and cause a phenomenon known as "fuel lock". That is, the bubble expands to the point where it actually blocks off the fuel flow. And then your bike conks out, you potter around, fuel slowly gets back down to the bowls, you restart the bike, and tootle off more bamboozled than ever.

Well, I took the man's advice, and never had that problem again.

Incidentally, you can get fuel lock happening with a poorly routed fuel line. If the line has a 'rise' at some point in its overall descent to the carburettors, then you can get a bubble trapped at that point... and you know the rest. So folks, if your bike is regularly conking out for no apparent reason, ditch the fuel filter and/or check the routing of your fuel line.

Carburetor breather tube issues

Now this problem is one of the more bizarre things I've ever run into -- but I suspect it happens fairly frequently. I share it here because whether you've got a GS1000S, GS1000G, GSX1100 or indeed any Jap bike with breather tubes/ vents for the carbies, then you may well encounter the same problem!

I'd had the GS1000G on the road for a couple of weeks, and despite a fair amount of fiddling with setting up the carburetors, there was one issue that just couldn't be tuned out. Basically, whenever I approached 90kph or higher on the freeway, after about 5-10 seconds the engine would start hesitating and losing a bit of power. Yes you could wind the throttle on more, but it still retained that 'hesitant' surging kind of behaviour, instead of smoothly holding its speed.

After a few rides, I began to notice that whenever I moved into the wake of a truck or van, the problem would disappear! This could mean two things. First, that with a touch of load on the throttle from the wind resistance, the carburetion wasn't right -- probably lean. But raising the jet needles 1/2 a notch made no difference, and at lower speeds there was no hesitation with light throttle. Hmm.

There was another possibility which I had read about on other forums, but never encountered myself. Namely, that at higher speeds either a vacuum or a pocket of higher pressure develops near the ends of the carburetor breather tubes/ outlets. This in turn affects the fuel mixture. To fix the problem, you simply need to change the location of the outlets, so that they sit in a still or steady pocket of air behind the carburetors (or wherever).

So, noting that the breather tubes were quite long (I'm not sure if they were original length or not), I trimmed about 5" off each one. And TA-DAAAAAAAA, problem gone!


Mark my words: the darstardly enemy of anyone dismantling a bike is... the bare thread! Now without delving into the mysteries of metallurgy, where you have a metal bolt or screw of one type (eg. zinc plated, or stainless steel, or brass) threaded into a different metal (eg. cast aluminium), you can get an electrolytic reaction happening where the metals touch. And then with time, they chemically weld themselves together, and no amount of tweaking, battering, thumping, or blow-torching is going to release the sucker. So that when the bolt or screw at last begins to turn, you find to your horror that you have just sheared off the head and the rest of it is down the hole, leering at you with an evil grin. Then you reach for the 'Ezy-outs'... but to really compound your misery you can shear these things off too, if you're not careful. Then you're REALLY stuffed.

The cure? Folks, you can look up all sorts of tricks on the internet if you like, but I'm here to tell you something that you perhaps have heard before, viz. prevention is better than cure!

That is, NEVER install a bare thread into anything. ALWAYS give it either a smudge of anti-seize grease, or a drop of oil, or some thread-locking compound. Sure, that smudge of grease might cost you another 5 minutes when you're installing new spark plugs, for example. But that's a lot less trouble than stripping the spark plug thread next time you're taking them out, isn't it.

Torque wrenches

When I first started working on bikes as an eager bike-bug-bitten lad, I subscribed to the age-old custom of doing up a bolt until you felt the thread go, and then backed things off 1/4 turn. Well OK, maybe not that brutal... but not far off. Then I heard of a wondrous device: the torque wrench. So I invested in a big 'un -- a 1/2" drive jobbie -- for doing up things like crankshaft rotor bolts and their ilk. But the smaller bolts on all my machines still suffered, as the manual specified torques so low (eg. 7 ft-lbs) that they were out of the big torque-wrench's range. So I just did them up all 'hand tight' and assumed that they were all evenly tightened.

Well, the cam cover on the Katana's motor had always frustrated me. I mean, it was always seeping or slowly weeping oil from some point of the gasket. I just assumed that it was warped in the casting somewhere. Until one day I put a straight edge against the mating surface, and found that it was spot-on. So why was it leaking all the time?

I started to wonder if, in spite of my best efforts, it wasn't done up evenly. So I bought a 1/4" drive torque wrench, ie. for low torque settings. Then I got a new gasket, and did up the cam cover bolts to the specified torque. And folks, IT HASN'T LEAKED SINCE: not a hint, not a whiff, not a wimper. So let that be a lesson to us all: just because your manual quotes a low torque setting for a bolt, doesn't mean that it doesn't matter!

Dealing with the evils of ethanol

In recent years I've noticed that the standard black rubber fuel line you can buy in auto stores, has been turning hard and brittle in next to no time at all. The likely cause of this is down to changing fuel chemistry -- and a number of articles I've read in recent times have pointed the finger at the ethanol now being added to our fuels. There is no doubt that the stuff is nasty to rubber and plastics, and the last thing you or I need is fuel dribbling onto a hot motor under our backsides as we're scooting along the freeway in a two-wheeled state of mind.

So I quizzed a friend who works in the BP refinery down in Kwinana, and he went and checked with the tekkies who operate their test-bench engines, as to what they use for fuel hose. The answer came back: 'Tygon'. Hmm... no idea where to buy that, I thought, so carried on with the usual black rubber stuff that goes hard with time, and just resigned myself to changing it every year or two. The last straw for me was when the best fuel line from a local supplier started to go hard in a matter of weeks. In desperation I asked Arnout what he uses... and he uttered the magic word again: 'Tygon'. This time I paid attention and bought a few metres of the stuff on eBay. It's a green-yellow semi-transparent fuel line that you can find readily on eBay in a range of sizes. I've been using it on my machines for the last few years, and while it might go a browner colour with time, it doesn't get hard and it doesn't fracture or crack or split. So if you're having trouble with your fuel lines going the distance, switch to some Tygon stuff and you'll find that it's much better!

And while I'm at it, I might as well point out that many fuel-lining resins for fixing rusted tanks also seem to succumb to the predations of ethanol with time. (NB. I can't verify this; it's just a suspicion.) But one product seems to be able to take whatever fuel you shove in the tank, and that's 'POR15'. It's an epoxy-based product, and again I've been using it for years now without it failing in any way. There may be other tank-lining products out there that do the trick, too, but POR15 is the one I can personally recommend. Like Tygon hose, it's also available on eBay... along with just about everything else inc. a spare set of false teeth for your mother-in-law.

Exhaust system paint

If like me you don't have a chromed exhaust system because (i) chrome is hideously expensive, (ii) it starts coming through with rust spots within 12 months, and (iii) you don't like all that blingy pipe-work... then you will of course have been painting your exhaust system at regular intervals with the usual hi-temp. paints that come in the rattle-cans. But they are expensive too (at least $20 a pop here in Oz), and the coating usually starts rusting through quite quickly anyhow. Is there a better solution out there?

I think there is! For just $15 at the hardware store, I found this 1 litre (or thereabouts) tin of BBQ paint.

It's billed at withstanding 1000 deg. celsius (exhaust headers hit about 600 degrees, from memory). You simply brush it on, no messy or wasteful overspray, and a little bit goes a long way, so a whole can is going to last you for AGES. There was a fair bit of smoke coming off the Katana's headers while the stuff 'cured', but now it's settled down it looks really good, and seems to be durable enough. Certainly much better than the expensive and short-lived spray coatings! The finish is a little blotchy in places (some parts appear more matt-black, while other parts are indeed the 'satin' quoted on the side of the can), but that's just a minor quibble. All in all, a great alternative to the usual sub-standard spray-on stuff.

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