® The Seven Deadly Sins of Custom Bike Building, Sin #1: Ignoring Basic Mechanics

I was test-riding a well-known Phoenix contractor's nitrous oxide equipped hotrod Harley bobber one afternoon when upon riding over a dip in the road the reach-for-the-sky "ape-hanger" handlebars tried to fold up like a collapsible lawn chair. Now, I am sure the armpits-in-the-wind crowd has their reasons for liking these handlebars, but one thing no one seems to consider is, with all the leverage such bars exert on their clamps, there just isn't any way to really securely tighten the handlebars short of welding them (I've resorted to pinning them). It's simple mechanics, and just one example of how often in custom building style preempts sensibility.

Big carburetors is another example. Only the high cost of aftermarket carburetors keeps them from festooning most customs; that and the fact that they dont "show" well. Carburetors are carefully matched to engine airspeed. Because of the nature of airflow through a tube, even a slightly larger carburetor than stock dramatically slows intake air speed, completely changing the engine's characteristics -- for the worse.

A far more serious illustration of mechanical mental blackout found on modified motorcycles is suspension modifications that include shortening the shocks' springs but leaving the damper rod unshortened. An accident waiting to happen as any good jolt will unseat those springs and whoa...! Saw this one a lot back in the day. Goes along with leaving the bearing spacer out of a wheel when installing it, another fairly common mistake.

A mechanical sin I have found myself committing is adjusting float levels in attempts to solve float bowl overflow problems. Now that I do carburetors full time it seems silly that anyone would do this, but it is extremely common. A manufacturer determines a float setting on the basis of air/fuel mixture needs, not leak prevention. A leaking carburetor can be caused by many things, including a cracked overflow standpipe, shrunken passage o-rings, warped castings, and blocked bowl venting systems, no name just a few. But it can never be due to the float adjustment unless it is grossly off and never is the solution to change the spec from stock. Never. Find and solve the problem, don't try to adjust it away. Not going to happen.

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