A friend of ours,
expressing more than a little discouragement after futilely tuning his Yamaha TT500, asked
for some help. We gave it, and thought you might be interested in sharing the experience.
The problems encountered and the solutions affected could be typical of nearly any bike,
not just a TT500. In fact, we'd venture to say most ill-running machines would respond to
the treatment to be prescribed.
The bike's owner related that a standard Mikuni carburetor was installed in place of the
original push-pull model, and since the installation, the engine was nearly impossible to
start. Low speed operation was atrocious, and the normal idle adjustments seemed to have
no effect whatsoever.
We attempted to start the engine. It wouldn't fire. A quick check revealed the total
absence of spark at the plug. The fix involved several simple but often neglected checks.
All of the external ignition wire connections were loose, and the connectors were covered
with a coating of fine silt-like powder (from a recent desert ride). The effect was much
like that of corrosion, and the cure the same. The connectors were cleaned with contact
cleaner, crimped slightly to tighten, and wrapped with tape. Besides sealing against dust
and moisture, the tape will prevent accidental disconnection of the plugs.
A nearly burned-through wire was routed away from the exhaust pipe, averting probable
future ignition failure. An inspection of the points revealed a coating of the same powder
(nasty stuff!). We cleaned the point surface with some #600 abrasive paper and contact
cleaner, then reset the point gap and timing. The dry point cam and felt wick were lubed,
and after checking for tight electrical connections, we replaced the point cover. The
fouled spark plug was replaced with a properly gapped new one.
A few more swift kicks again failed to ignite the beast. There were, however, several
explosive gasps which showed we were on the right track. To gain access to the carb, the
seat and gas tank were removed. Our initial inspection found these faults:
A plastic float bowl vent hose, resting on the
exhaust pipe, was melted closed.
The throttle cable was improperly adjusted,
preventing the slide from closing fully.
The throttle cable was also improperly routed,
causing it to bind.
The carb-to-engine rubber connector tube was
improperly clamped, allowing a slight air leak
The idle mixture screw was adjusted fully closed,
no doubt because of the above conditions.
The foam air filter was improperly oiled.
All these faults were discovered by a simple, common
sense visual check and were easily corrected. With the idle mixture screw set at 1 1/2
turns, this beast-turned-beauty fired on the second kick. We allowed it to warm up for
several minutes, then adjusted the idle mixture speed. A quick road test confirmed our
original suspicions. There was nothing originally wrong with this motorcycle that a little
attention couldn't cure. We used no exotic tools, or replaced any parts other than the
spark plug. Had the owner taken the bike to an honest, competent shop, the bill would have
been substantial-and a total waste of money! (The man was duly reprimanded!) The lesson to
be learned is obvious: Although you can't always do everything, always do everything you
can. More often than not it will be enough to keep you rolling happily, rather than leave
you raving madly.