Gas fumes

Ok, this both is and isn't a vintage mc question.

I've been working to finish my detached garage so I can use it for something other than parking my 1979 KZ750. I insulated it and hung drywall. Also put up new weatherstripping around all the doors. And installed a window unit AC to keep it cool.

Ever since I sealed up the space, I've been getting a really strong gas smell in the garage. Never noticed it before and the bike has been housed here for about four years.

I've been trying to hunt and fix any minor gas leaks I can find. There were a few, around the carb float bowls but they were pretty minor. It's not like I'm leaving gas puddles on the floor. I also replaced the gas cap gasket. There's still one float bowl drain screw that's weeping a tiny bit of gas. But the smell in the garage is still pretty strong.

It's got me wondering if a 40 year old carbureted bike is just always going to produce some gas fumes.

What do you think? Anyone else run into this? Am I chasing my own tail trying to fix every minor gas weep? Do I need to install some ventilation instead?

You might try starting it up, then turn the petcock to off till you drain the float bowls. Let it sit a couple days. If you still smell fuel , probably it's not them.

Yeah, or drain the float bowls. That's the kind of trouble shooting I've been doing and eliminating as many small leaks as I can.

I guess my question is more, "is it just normal for a 40 year old bike to have some gas fumes?" Because if so, I need to look into ventilating the garage.

Yes, there will be some, especially right after a ride. Heat from the engine will cause the fuel in the tank to heat up and expand. The fuel tank, like the carbs, vents to atmosphere, hence the fumes.
You could try letting it cool to ambient temperature outside to see if that will reduce the fumes.
Even after the temperature equalizes, there will be a little evaporation venting into the garage, so it will not be absolutely fume free.

I think the answer is yes, 40 year old bikes give off fumes. The fuel tank is vented to the atmosphere as are the carbs. Draining the carbs will help but the tank will still vent.

You could try removing the fuel tank and then put it in the garage with the bike outside the garage to see if the odor is from the tank. If that does not produce the fuel smell then you can focus on ensuring the carbs are absolutely leak free. Ed

Yeah, I think I'm going to need add some venting. I'm not seeing any more fuel leaks and the fumes are still pretty annoying.

I don't want to go with a full bathroom exhaust fan routed out the roof. That seems like overkill, plus I just want it to work passively when I'm not in the garage. Time to get creative I guess.

Many types of 'gable vents' available, that if installed at both ends offer good cross-ventilation without cutting into the roof.

Unfortunately those won't work. The ceiling is drywalled so the gables are behind drywall and six inches of insulation.

I'm considering putting some sort of passive vent in the ceiling, something like you put in soffits. They would let air flow up into the "attic" space above the garage. From there it would flow out through the roof's ridge vent. That's what I think the fumes did before I insulated everything. I'd just be opening that path back up to them again.

But I know that's generally a construction no-no as it can lead to moisture problems and increases the chance of fire getting up into the attic if the building were ever to catch on fire. But having gas fumes accumulate in the garage isn't exactly safe either. I'm also not sure it would allow enough airflow.

Rather than trying to modify the garage I would first find and correct the source of the gas fumes. The bike should not be emitting them, so there is a problem that can (and should) be found and solved. Ed

650ed wrote: Rather than trying to modify the garage I would first find and correct the source of the gas fumes. The bike should not be emitting them, so there is a problem that can (and should) be found and solved. Ed

Well, that was the question I posed in the original post. It seemed like the consensus was that a 40 year old carbureted bike was going to produce some fumes.

I'm at the point where I'm not seeing any more leaks. There might be one on one of the float drain screws. But it's small and slow (replacement screws and copper gaskets are on the way). I put a paper towel under the carbs overnight and in the morning saw no evidence of drips. There was still a fairly strong gas smell.

I've drained the bowls and am waiting to see how rapidly the smell builds up today.

Are the carbs vented under the seat? Is the petcock shutting off the fuel? Sometimes when I forget to turn it off I get the smell of gas. Float valve. I fixed it but have to remember to turn off the petcock. It's 115+ during the day and 80/90's at night out here. I leave the door open to keep the heat from building up and close it at night. In the morning when I come in and smell gas it's because the petcock is still on. :blush:
Steve