In the good old days before the Environmental Protection Agency got going, motorcycling
was in some regards safer. For example; if your carburetor float valve should stick open,
the fuel would go through the overflow tube in your carb’s float bowl and end up on the
ground. Now it goes into your cylinder and ultimately mixes with your oil.
A most dangerous EPA mandate requires that motorcycle gas caps can allow air to enter
the gas tank, but not allow gas fumes to exit. The problem with such a delicate
arrangement is that it requires some very intricate valving in the gas cap to do the job. If
the system fails, your fuel flow can be interrupted by a vacuum created inside the tank.
With over 185,000 miles on DR’s and in excess of 270,000 miles on KLR650A’s, I’ve
been bitten by the gas tank vacuum bug once on the DR and several times on a KLR.
In the case of my 2002 DR650SE, I was riding my nearly new, completely stock bike
southbound near Laurence Welk’s resort north of Escondido when my engine suddenly
stopped running. Fortunately traffic was light and I was able to coast to the side of the
road where I diagnosed and fixed the problem.
In the case of the KL-650A the problem was less dramatic and thus more difficult to
diagnose. As I wrote in a previous article, I began to “run out of gas” with fewer and fewer
miles on the trip odometer. In two cases the bike actually quit running. I finally had a
bright idea and disassembled the gas cap and discovered the one-way neoprene (red)
air valve had become defective.
Why is this “one way” gas cap air valve failure dangerous you ask? In the first instance I
had been in very heavy multi-lane traffic coming out of Los Angeles less than an hour
before my DR suddenly quit running. How do you get from the middle freeway lane to the
side of the road with no engine and traffic all around you running 65 to 85 mph?
My failures on the KLR occurred on two lanes so conditions weren’t as dangerous, just
inconvenient. In one case Rod Morris transported me 35 miles down Hwy 94 on his 1000
V-Strom so I could activate my car and bike trailer. Rod’s max lean angles didn’t bother
me, but the DL1000 had to grunt a little hauling 400 plus pounds of old meat and bone.
Since I don’t want to assume any liability or piss-off the EPA I can only tell you that this
dangerous gas cap problem on the DR and KLR (and probably other models) can only
be fixed by removing the one way neoprene valving before it can deteriorate and
ultimately compromise air flow. It’s too bad that in order to insure our own safety we must
violate federal law. I am not making a recommendation here, just defining the problem we
By the way, the smog purge system itself doesn’t cause a running problem that I know of
except of course in the case of the gas cap failure. One exception would be that if you
ride a lot of off-road like we do, the canister itself will probably eventually plug up with dirt
and cease to function.
Don’t get me wrong, I believe as do 97% of scientists that carbon dioxide produced by
humans is dramatically speeding up global climate change. I’m just not willing to die
prematurely in an effort to “catch some fumes”. On the other hand, I run all my bikes in
stock EPA mandated state of tune from the air intake tube to the end of the stock muffler.
After all, it’s what comes out of the tail pipe that really does the most damage to our