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 every time 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 ~

Well, according to Wikipedia most of the mechanic said is hogwash. This is the explanation I read:

Backfire in an automobile engine typically results from various malfunctions related to the air to fuel ratio. Usually, backfiring occurs in carbureted engines that are running lean where the air fuel mixture has insufficient fuel. ("Running lean" is typically a sign of mal-adjusted carburetors or fuel injection where there is not enough fuel for the amount of air). Afterfire occurs in engines that have an emission system malfunction (air injection system diverter valve), exhaust leak or unburnt fuel in an exhaust system in which the catalytic converter has been removed. When a driver shifts up and lets off the accelerator, the engine has a moment of running rich or with insufficient oxygen. This causes an incomplete burn which causes the fumes to explode in the exhaust system. The leak itself is the most dangerous aspect. Without it, the mixture would cool enough not to explode. A fuel injected engine may backfire if an intake leak is present (causing the engine to run lean), or a fuel injection component such as an air-flow sensor is defective.

The first problem with fuel dripping out of the carb is serious. Serious enough to cause an engine fire. I know the hard way.

First, their has to be something wrong with the evaporative fuel system. See if the truck backfires with the gas cap loose. If it doesn't it, most definitely the evaporative fuel system. That system usually consists of a charcoal canester and a solenoid valve.
The backfireing, I would guess would happen more easily on a full tank after the truck has sat for a while.

The charcoal canister could be bad.