BACKFIRING.... because of filling the gas tank....???

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

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.

Hey Rodan, ever heard of a 'universal life policy'--now I know what it REALLY means: a policy that covers the life of whomever drives that truck. Now where do we buy one right quick? s

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

Can you explain a little more..I would have intuitively thought that a tank with a large vapor space, particularly in summer, would be more of a problem.

Okay, for gas to come out of the tank, air needs to get into it to displace it. Back in the seventies, gas tanks had holes in them to let the air in. They'd also let out gas fumes, which was bad, so that got banned.

So now, at what is presumably the highest point in the tank, there is a hose which goes to a charcoal canister. Air can get through the canister to displace fuel, but heavy molecules like gasoline vapor cannot.

If you keep pumping fuel into the tank under pressure, you will eventually displace all the air in the tank and eliminate all the vapor space... and since the filler neck is higher than the highest part of the tank, fuel is always under at least a little pressure when it goes in there. Do that enough and you're apt to get a little fuel into the canister. Does not take much to wreck the thing.

If there is a vapor space in the tank, it's because the tank vent is below the lowest point in the tank.... in which case the same thing applies.

--scott

So you are saying that if you fill the tank too full, liquid might go into the cannister hose and into the charcoal? I thought they put liquid stop valves in there to deter that, but maybe not.

In any case, the fuel in the tank will have a vapor pressure, no matter how full the tank is, and some of that will bleed into the charcoal cannister if the temperature is warm enough. I read up on it a little last night, and my book said that these tank configurations allow air to enter the tank (one way) as the fuel is consumed (which sounds a little like a hazardous practice). Even if that happens, the vapor space will be saturated with gasoline vapor, depending upon the temperature and the partial pressures of the components.

Right. And they might be putting effective valves in there to stop that on modern cars, I don't know. They sure didn't in the eighties.

Right, this is good. This is what the canister is for!

Right!

--scott