Bike: Fuel Pump Filter

Leak.

What started out as a great day of dual sporting, ended with a nerve wracking ride home. Just as we found our way off the trail, my bike was not running correctly...whatsoever. Since I had taken off from the garage on my bike and didn't want to call a rescue truck, I limped it all the way back.

My bike sat dormant in the garage, waiting for me to tear into it and solve the problem.


How it all started:

My friend Brandon and I rode out on a pretty average PNW summer day, to a hush-hush area 45 minutes east of Everett. We followed some freshly cut singletrack deep into some very overgrown woods. Along the way, I took us up to a hilltop view which we could see the Seattle skyline from.

Pictured: Brandon Kovaly.

Most of the time on the trail, the bike was running just fine. The 500 was actually handled the gnarly parts extremely well for being in -1 -5 gearing. Towards the end of the ride, when I was starting to get burnt out from picking up my bike too many times, I started getting some strong decel popping. It continued to get increasingly worse the more I rode, and eventually turned into a strong engine sputter and sporadic choking that wouldn't allow a smooth increase in RPMs across the throttle range.

Once we found our way back onto the public road, my bike shut itself off. It took a substantial amount of electric and kick start to get it going, which had the best results when I used them both at the same time as suggested by Brandon. I had to repeat the process about 4-5 times. Eventually, I found that if I kept the RPMs high enough, I could keep the engine running.

Following getting home, I messed around with a few things I thought might be the problem, suggested by some friends in my online 500/501 forum. After a while, I finally noticed my fuel pump was making an odd noise. I popped the fuel cap off, and cycled the killswitch, and noticed a mist cloud of gasoline forming in the empty part of the tank as the fuel pump was doing it's initial startup priming. Following, I spent a few days doing research on fuel pumps in between catching up on other work. A tip from my friend Casey was to remove the pump, and possibly replace something that had punctured or torn, hopefully just swapping a bit of submersible fuel line.

Eventually, I had it hauled over to my buddy Travis' house to tear it apart and diagnose the issue.

Travis Zylstra's convertible BMW moto-hauler.

Travis Zylstra's convertible BMW moto-hauler.


Diagnosis/Repair:

Since we were unable to see where the point of origin for the leak was by looking into the tank, even with a bright LED flashlight, the pump was immediately pulled.

Closer investigation of all the pump lines and components didn't reveal anything obvious. Travis had the idea of carefully pumping some air into the inlet, which immediately showed us that the fuel filter had a failure point, allowing fuel to shoot out of a broken seam.

High-pressure jet mist of fuel.

We decided the easiest way to remedy the situation was to remove the entire line that the fuel filter was in-line with, and replace the whole thing with a new fuel line.

Installing the new 1/4" submersible fuel hose with a couple 11-13mm clamps.

Grinding the ends of the clamp bolts off to prevent any damage to the rest of the components, or the inner sides of the tank itself.

Photo: Travis Zylstra

Re-installed the pump and tank. After a bunch of initial starter motor cycles, the pump finally got the fuel to the engine, and the bike started beautifully and ran like a champ. I immediately took it for test ride, and it ran absolutely perfect. As a matter of fact, there was a substantial power increase.

Curious, we decided to crack the filter open, only to find that the element was totally soiled.

Now that I know it works, I will clamp in a fresh fuel filter in-line with the new hose.

Travis also gave me a hand in straightening my front axle/forks, which had been causing the bike to dive to the right anytime I took my hands off of the handlebars.

Always a good feeling to have your bike back in working condition.