I'm interested in learning more about the innards of the 3bbl carbs
especially the power valve circuit. I have a persistent problem of the
power valve draining the carb overnight on all four operating gen II's.
I'm giving serious consideration to changing over to the Webber solution
on the daily drivers.
Don't mother-in-laws generally sit in the back seat?
I'm not familiar with that carb. Give more info about this draining.
Usually a power valve that is open (vacuum actuated) or closed
(mechanically actuated), when the engine is not operating, does
nothing. Fuel is in the float bowl, it is drawn UP the pipe (fuel
nozzle) to the venturi when the engine is running off idle. The fuel
goes through the main jet(s) first, from the bowl. When the power
valve opens, it allows additional fuel to be drawn UP the pipe (fuel
nozzle). Power valves are usually open (vacuum actuated) when the
engine is not running. High manifold vacuum (throttle valve not open
much) keeps the power valve closed. Wide-open-throttle, when the
engine needs more fuel delivered to the venturi, manifold vacuum
drops to about zero, power valve opens.
Is the float bowl empty of gas after sitting overnight?
Good point... I think they're supposed to sit in the back seat... they
may have different opinions about that though. Especially the ones
that want to 'assist'.
In the 3bbl, it comes out the bottom.
If I had my druthers, I'd prefer a design without a power valve. I just
don't see an advantage.
The old Stromberg 2bbls and AFBs were great carbs and neither had a
power valve. Very trouble free and when it came time for a rebuild, it
was a simple task.
then you have a leak. enrichment pump diaphragm or maybe even porosity
of the bowl material. as m.a.s. points out, fuel is drawn /up/ out of
the bowl by partial vacuums - it is not gravity fed anywhere, and thus
cannot drain unless there is a significant problem.
time to upgrade to fuel injection dude. unless you're running something
like two twin weber dcoe40's, fuel injection is absolutely the way to go.
nomina rutrum rutrum
What is not according to the shop manual? Is the float bowl completely empty?
You wont know that unless you take the top off the carb off. Just because
you can't see fuel through the sight glass does not mean its completely
Fuel normally evaporates out of the float bowl (it's supposed to be
captured by the evaporative control system), but it would take weeks to
evaporate all the fuel out. If the fuel level really goes down a lot
overnight, the engine will take many cranks to start up in the morning
(the fuel pump has to fill up the float bowl which takes time). Is it
Maybe the casting has a crack in it. Maybe a drill-way plug is leaking
(if it has drill-way plugs). Drill-ways are holes drilled into the casting
to intersect other drill-ways if a circuit (a drill-way) has to change
directions. The plugs are usually brass or lead or soft steel or aluminium.
The power valve sits on the bottom
Just like almost every other carb. The fuel has to go UP the nozzle to the
venturi, which is above the fuel level. Is the evap system pressurizing
the float bowl?
But a carburettor is a computer! It's not an electronic computer, its
a mechanical/hydraulic/pneumatic computer! Some do have electric
inputs (i.e. an electric choke heater). It's programed (calibrated) to
deliver the proper fuel mixture (which is dynamic, depending on what
the engine has to do).
A diesel engine fuel pump is a computer also, a mechanical computer.
A distributor is a computer (vacuum advance/mechanical advance).
Textile looms from the eighteen-hundreds were mechanical computers,
and player pianos. etc.
Fix what ya got. Is a Webber a fix? Maybe... I don't know. Will a Webber
pass your state emissions?
The RAD-mounted sensor is the for cooling fan.
The ENGINE-mounted sensor is for the dashboard gauge.
If the fan runs too often and too long, then the rad sensor is simply
faulty and in need of replacement by a new one of the very same rating as
If your thermostat is of the correct rating and is in good working-order,
then it will properly control the engine-coolant temperature regardless of
what the rad fan wants to do.
Despite the age of your ride, you should be using genuine Honda parts, not
aftermarket. If you're using aftermarket parts, that's the most likely
explanation for whatever erroneous behavior you're experiencing. Unless
you've got a deeper and more fundamental problem, like poor combustion, or
low compression, etc.
Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here.
All logos and trade names are the property of their respective owners.