We have a strange problem with one of the Ice Cream Trucks.  The truck
has had issues over the last few weeks with BACKFIRING.  All sorts of
causes/solutions have been tried.

The latest one, and one that SEEMS to have corrected the problem is
somehow, when we put gas in the tank....  it would cause the
carbuerator to overfill...  actually what we saw was gas dripping out
of the engine.  They did something with some kind of OVERFILL TANK and
something to do with a hose.

The mechanic... who we are somewhat skeptical about said NOT to
overfill the gas tank.  Just put the gas in until it clicks off.
Well....  the problem is, sometimes it will click off after only 5 or
10 dollars worth.  We KNOW that we need more gas than this.

Now... does all this make any sense?  Can putting a little too much
gas somehow FLOOD the carbuerator causing gas to drip out the front of
the engine?  What would make the gas pump shut off all the time way
sooner than it should?

One last question.  Is the BACKFIRING dangerous?  When it was doing
this the other day, we could actually see FLAMES coming out of the
tailpipe everytime it backfired.  Our boss said that isn't really
dangerous and that it was safe to drive.

I am not sure of the make-model of the truck but what do you guys
think about all of this?     Thanks in advance     ~ david ~
________________________________________________________

I love it: gas dripping out of the front of the engine; some kind
of overfill tank; something to so with a hose; pump shutting off
too soon; make and model unknown; what the boss said; what
the mechanic said; multiple undisclosed solutions tried; query
whether backfiring is dangerous ......

There is something here for everyone.  This one should be good
for hours of posts begging for more descriptive details of the
symptoms or blindly offering solutions for multiple  scenarios.

This is one of the most creative trolls I have ever seen.

Good luck.

Rodan.

What causes have you looked for and what solutions have you tried?

That has nothing to do with putting gas in the tank.  He's talking about
a bad seal or a bad carb float which is causing the carb to flood out.
This probably won't cause backfiring but it might cause all kinds of other
unpleasant problems.

The reason you don't want to overfill the tank is that if you put too
much gas in the tank, it will contaminate the charcoal canister that is
used to keep gas fumes from escaping into the outside air.  This has nothing
to do with backfiring, but it will prevent your ice cream truck from smelling
like gas.  Gas fumes do not go well with ice cream.

No, these are unrelated things.  And the gas pump shuts off a little early
because there is air in the tank.  It won't hurt to keep filling a second
time if you are absolutely sure the tank is very low, but don't do it when
it's close to being full.

It's probably not dangerous to you, but it's going to ruin the truck in
very short order.  

Backfiring is caused when the fuel in the cylinder combusts while the
valve is open.  This is either because the valve timing is screwed up so
the valve is opened too early, or because the spark timing is screwed up and
the spark is fired too late.  

Backfiring through the tailpipe is fairly harmless although it will wreck
the muffler pretty quickly.  Backfiring through the carb is a good way to
get an engine fire.  As long as it is always backfiring through the tailpipe,
the main worry is ruining the muffler and the valves.

I have no idea because I don't know what the mechanic actually did that
relates to the backfiring.

I think you have three unrelated issues here:  the carb float, the tank
overflowing, and backfiring.
--scott