> > 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.
--
Paul Lamar ...No rotor no motor.
For what it's worth, I tend to agree with Dave that there are
probably more engine fires since EFI became widespread.
This is hardly a scientific sample, but two years ago I witnesses a
crash in front of my farm in which a brand new Ford F-150 pickup
smashed into the back of a farm tractor pulling a trailer. I just
happened to be looking out my front window and there was a huge
fireball almost instantly. I bolted out the front door and sprinted
the hundred yards or so down my drive in my slippers and by the time
I got there the truck was completely engulfed.
My neighbor across the road ran over with a fire extinguisher and
tried to put it out, but there was no chance. By the time fire crews
arrived the truck was completely burned out. The blaze was
huge. Luckily the driver and passenger got out, but the guy on the
tractor wasn't so lucky -- he was fatally injured on impact.
In the last few years I have seen more cars burning on the side of
the highway. This is something I never saw in years past.
I tried to find some statistical info, but the last NHTSA study is
from 1990. They did find that fire frequency had increased even then.
http://www.autosafety.org/article.php?scid=96&did=533
<http://www.autosafety.org/article.php?scid=96&did=533>
A more recent article from 2004 appears to suggest that fires are
increasing at a high rate, despite overall safer vehicles.
http://www.autosafety.org/article.php?did=1193&scid=179
<http://www.autosafety.org/article.php?did=1193&scid=179>
It's hard to draw cause and effect conclusions from this, but it
does reinforce my nervousness about flying with an
automotive-derived EFI. Just my personal preference, but I would
rather go with a carb and low-pressure fuel. Paul's slide throttle
carb could be the best bet.
Regards,
Gordon.
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