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What's that gasoline smell? A ProjectLab mystery

By Andrew Reuter
July 14, 2015

My wife and I recently returned home from a day-long road trip. A cloud of fumes greeted us in the garage.

At first, we blamed the smell on oil-based paint that Abby had been using to refurbish a sewing table. Maybe a can had popped open?

I hammered the lids down and went on my way.

Days passed. The fog intensified. It smelled more and more like gasoline.

Something had to be leaking. But what? The suspects were numerous. My garage could double as a rusty-small-engine museum.

Finally, I got a chance to go sniffing around. I started with the tiller.

This thing had sat unused and unstartable for more than a year, making it a likely suspect for rust deterioration. It also was light, so it would be easy to remove from the garage in the case of a massive gas leak. (That factor was based more on wishful thinking than logic.)

Conclusion: No gas smell. Tight as a drum, despite my neglect.

I decided to work my way around the garage in a circle from here. The next suspect: The snowblower. While this was a loyal, reliable machine, it still needed to be ruled out for the sake of science. Also, the gasoline smell did seem to be coming from that side of the garage.

The culprit! Gasoline had soaked the wood rolling platform below the blower. Second try was the charm.

Directly above the gas spot: The carburetor.

The bottom of the bowl, which is where gasoline collects before being sucked into the engine, was wet with fuel. So was the vent tube, where excess gas exits if too much fuel gets into the carb.

This actually was welcome news. There probably was no hole to be patched in a fuel line or tank. Still, I had to figure out why the carb was dumping out gas.

Did the throttle stick open? That might send a torrent of gas into the carburetor. But I hadn't touched the snowblower in months. This seemed unlikely.

Had a carburetor seal failed? This would explain the gas on the bottom of the bowl. But why would there be gas dumping out of the overflow tube? That shouldn't happen in this scenario.

I wasn't necessarily stumped at this point—but I didn't feel like going on some wild goose chase, either. I pulled out my phone and dialed up the former owner of the machine: Neil, Abby's dad.

First, shut off the gas, he advised.

Look, most of my small-engine experience has been spent with motorcycles. On motorcycles, the gas shutoff is a metal valve called a petcock. These generally are easy to find because they are big and directly connected to the gas tank.

My riding lawnmower doesn't even have an oil filter, much less a fuel shutoff. I just assumed that snowblower/lawnmower engineers planned for these machines to burn up before needing significant service. I didn't even look for a shutoff on the snowblower.

Yet there it was. A screw that blocked the fuel line when tightened.

Right in front of my face.

I turned the gas off. For now, no more fumes would fill the garage. But the deeper mystery remained. Why was the snowblower leaking gas?

Neil and I quickly ran through a few theories. Stuck float? Loose tube? Magic?

We settled on fuel expansion.

The concept: As the temperature in the garage rose, gasoline in the garage expanded. Gas tanks and gas cans have built-in vents to manage this pressure. Maybe the gas in this carb grew too huge, escaping by dripping out of the vent tube and seeping out of the seals.

I like this theory for a couple of reasons.

For one, the first day I noticed the smell was among the first hot days of the year. The timing aligned.

For two, this theory means I don't have to do anything with the snowblower for now. All I can do is wait till the fall and open the fuel shutoff valve again. If the carb doesn't leak, then I will be even more confident that we were right. If it does leak, then eh. At least I should have time to fix the real problem before winter comes.

Think I'm wrong? Was the problem magic after all? Let me know. Send me an email at [email protected] or find me on Twitter at @andrewreuter.