> Dave,
     > Having had to deal with many carbs and FI systems over the years I
     > would
     > respectfully disagree that carbs are safer. While there is higher
     > pressuure fuel in a FI there are systems designed (hoses and ends) to
     > deal with it. The float valve in any typical carb is the weak
    link. The
     > fact that the gas is pumped in by "only" 6 PSI is little comfort
    when
     > you
     > have an engine fire. In fact if turned off the FI system provides
    less
     > to burn. (No float bowl)
     > Bill Jepson


    Hi Bill,
    I see your point but the reasoning was more as follows:
    A leaking hose in FI produces a fine mist which, if ignited, makes the
    cowl a bomb.
    A carb leak will more likely produce a fire, so turn off the fuel and
    remove the source.
    Of course, these are only likely scenarios; the carb leak because of a
    stuck float valve could also lead to an explosion; but the high
    pressure mist in the FI example is almost guaranteed to explode. It was
    more that the explosion was the worry rather than the fire.

    We have a couple of old bike racers in our club  and we spoke at length
    on this possibility and the general opinion was that float valves
    rarely stuck, and when they did, often the valve stuck in the closed
    position; cutting off the fuel. Also the Bing and Mikuni 'caged' valves
    are much more reliable than the old Amal "free" valves.

    Further to this debate, in your bike days, how common was a stuck float
    valve and in what position?

    Thanks for your valued comments, BR, Dave McC

Dave,
 Older bikes are a bit of a different subject since gravity feed was
normally used. We saw both stuck open and stuck closed, the latter
mostly on machines that had been inactive. With fuel pumps, and that is
very common now, stuck open is more common. Usually stuck open float
valves being caused by debris. Running a good filter reduces this greatly.
 With respect to the under cowl mist being sure to cause an explosion I
must say bunk, sorry. Few cars built any time in the last decade have
had carbs, all are fuel injection. You don't see sudden fire balls on
the road. It would be just as likely as with an aircraft with many cars
having extraordinary under hood temps. Hell if it was common the
resultant lawsuits would be all over the papers. Additionally the number
of leaking and ill-maintained cars would make ANY comparison to planes
look like a tiny sample of generally pampered engines. On racing engines
I would say I have seen far more mechanical failures than fuel failures.
Put more simply, I would say if you are more comfortable with carbs
RUN THEM. You should remember though that more aircraft accidents are
attributable to carburator icing than any kind of fires. FI engines
don't have a problem with icing. I had the carb on my 172 ice up once on
a night flight into Montery, scared the crap out of me honestly. I was
getting ready to let down for landing and the normal "carb heat on for
decent" proceedure saved the rookie from further misfortune.
Bill Jepson

Hi again Bill,
I appreciate your comments ref icing up the 172, I was aboard a Stinson
that dead sticked into a field due to carb icing. Overturned, I exited
on hands and knees!

However, since your last remarks, I had some time with old aircraft
engineers, they say most airplane carbs in use today are Marvel
-Schiebler, MA 3, MA3-4, MA 5 etc  or derivatives , all have floats and
float valves and no real history of sticking float valves. Some time
back, 10-15 years, there was a problem with "sinking" floats, but this
was mostly due to corrosion of the brass float, because of water in the
float bowl, the float developed a hole and sunk; and was fixed by
installing "plastic floats". AD as I recall.

As regards carb icing; this should be called by its correct name-
"Induction Icing". If you introduce  gasoline into a a long runner, you
will get icing due to the latent heat of vaporization;  whether it is
by carb or by injector, you will have the possibility of induction
icing.  Just because the fuel is "injected" does not make the system
ice proof.  Injecting fuel close to the valve, (warm head), all but
eliminates the possibility of icing, but if we inject fuel at the bell
mouth, then we can expect induction icing. A good reason to introduce
fuel into Paul's slide throttle;  close to the port.

As regards being 'comfortable' with carbs, I am, - have been for 40
years;   but  I am "not comfortable" yet with hi pressure FI. I have
been through the auto wrecking yards quite often over recent years, I
am a hotrodder, and underhood fires are far more common than you
suggest.

BR, Dave McC


I had C172 float sink on me one time. Hard to keep that sucker
running with the leaning knob.