Gas in airbox - Kz750

External Since: Jun 29, 2003 Posts: 1

I have a KZ750-K1, belt drive, twin, 1983. After it sits on the
sidestand for a period of time (couple of hours at least), it collects
an amount of fuel in the air cleaner box.

When the bike is raised to the perpendicular position (preparatory to
raising the side stand), this fuel "gushes" out and leave a nasty
stain on my driveway.

Connections to the air cleaner box are
1) air ducts to the carbs (these slope down very slightly from the
airbox to each carb, so I don't think it is running back in from them.
2) a vacuum line from the carbs to the vacuum switch valve (see
below) and to the fuel tank petcock.
3) a vacuum switch valve that has lines coming back from the air
suction valves in the exhaust ports; provides clean air to the exhaust
port under normal running, but shuts off that air under deceleration
to prevent back-firing.

The tank and petcock are *not* leaking (all new o-rings, diaphragm in
petcock).

Anyone have a similar experience (any or all bikes), or any idea where
that pesky gas might be coming from?

Thanks

Denny

External Since: Oct 23, 2003 Posts: 78

denny_rich DeleteThis @ameritech.net (Denny) wrote in message ...
> I have a KZ750-K1, belt drive, twin, 1983. After it sits on the
> sidestand for a period of time (couple of hours at least), it collects
> an amount of fuel in the air cleaner box.
>
> When the bike is raised to the perpendicular position (preparatory to
> raising the side stand), this fuel "gushes" out and leave a nasty
> stain on my driveway.
>
> Connections to the air cleaner box are
> 1) air ducts to the carbs (these slope down very slightly from the
> airbox to each carb, so I don't think it is running back in from them.
> 2) a vacuum line from the carbs to the vacuum switch valve (see
> below) and to the fuel tank petcock.
> 3) a vacuum switch valve that has lines coming back from the air
> suction valves in the exhaust ports; provides clean air to the exhaust
> port under normal running, but shuts off that air under deceleration
> to prevent back-firing.
>
> The tank and petcock are *not* leaking (all new o-rings, diaphragm in
> petcock).
>
> Anyone have a similar experience (any or all bikes), or any idea where
> that pesky gas might be coming from?

I suspect that by a "gush" of fuel, you mean several ounces at least, which
is significant compared to the small ammount of fuel in your carburator
bowls. It's coming from somewhere, and that somewhere must start with the
tank. You won't get very much out of the carburators if it's all staying
in in the gas tank. That it takes several hours points to a slow leak
somewhere important.

I'd check that petcock again. First ensure that you're not leaving it in
the prime position. (That's akin to "is your computer plugged in?")
Barring such simple solutions, disconnect all the hoses (both?) from the
petcock and put a piece of paper under it to catch any gasoline drips.
New parts don't always work, especially in old machines.