Home Feb 2010 Vol 10 - No 2
Feb 2010 Vol 10 - No 2 - Fuel Pump Gravity Feed by Dave Wolf PDF Print E-mail
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Thursday, 04 March 2010 19:19
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Feb 2010 Vol 10 - No 2
Group Riding Formations- Cluster or Solo? By Ben Harper
The Valve Stem by Alex Ford
Fuel Pump Gravity Feed by Dave Wolf
Rear Brake Switch by Dave Wolf
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Fuel Pump Gravity Feed by Dave Wolf

So today it finally caught up. God gave me a warning and enough time to order a new pump, but I didn't do it.  On Highway 18 today sputter, stall. Sputter, sputter, etc. I pulled over, and cycled the key about 20 times. It started up, and I rode about 1/4 mile before it died again.  I took off gas cap (I did the vent mod) but still nothing. With every key turn, I got a single "click" out of the fuel pump. Or, it could have been a relay.
I was in the middle of trying to start it again when the people who took me in were driving by and stopped. I got a ride back to where I live, (just in time), and made about 15-20 calls to automotive and motorcycle shops to try to get a 1 PSI fuel pump. *Nobody* has that. The best I could find online is a 1-2 PSI pump.
At 2 PSI you are doubling the effective pressure against the needle valves in the carburetors. So, I said, "let me get my tools and I will try the gravity feed."
So, I did, and on the side of the road, I did some bike surgery.  I cut the fuel pump out of the circuit, and disconnected it electrically, and finally just removed it.  I put the fuel pump in my backpack, and will take it apart and share what I find here.  Anyway, all I had to do was remove a bunch of gratuitously long fuel lines, and turn this "T":

The "T" was previously facing the back of the bike. Its purpose is to split the flow of fuel to each carburetor. I loosened the clamps one at a time and rotated it towards the front of the bike.  This was because the fuel supply changed, and I wanted as short of a run as possible. This is literally the hardest thing I had to do.
I cut a small 2" section of fuel line and attached the fuel filter directly to the petcock. I had to cut the fuel line going to the "T" because it was far too long. At that point, I simply connected what was left of the fuel line going to the "T", turned the gas on, put everything back together and took off.
I have a little over 100 miles (I get 15-160 miles to reserve) on this gravity feed, and I can tell you guys, it works great.  Now, there's a section of the line that looks like it goes up higher than the bottom of the fuel tank, and that worries me a little.  Tomorrow, I am going to take the air box out and do a little more surgery to ensure the run goes straight DOWN. But so far it's great.
Let me share with you my experiences:
1. The bike vibrates a lot less. I synced the carbs less than 500 miles ago. At 70 MPH the rearview mirror is actually almost usable. Previously it was only useful for making out basic shapes.
2. The mysterious and insanely annoying BLUBLUBLUBLUBLUBLUB sound when at a stop or trying to sync the carbs at 1,000 rpm with a hot engine has gone away. Now it idles at a very wonderfully smooth and pleasing rate in traffic.
3. I have to wonder, all of those times my motorcycle had difficult (not in the cold, I know the cold affects the way it starts) starting, if it was the fuel pump intermittently working.
So I couldn't wait, and took the fuel pump apart now.
Here is what I discovered (and the problem!):
The fuel pump is surprisingly easy to take apart. The tabs securing the pump half are easily bent back. However, you will not have to mess with this half of the pump. (but if you do, be careful not to dent the pump housing! The only way you would want to break into this part is it the pump will not shut off and you feel confident enough to service a one-way valve!)
The other half is secured with just a single screw! This screw is also the ground connection screw.
This is when I discovered the problem, friends. Had I of known this, I would not have had to go to gravity feed on the side of the road. As some of you may know, I frequently ride off road, partly because I have to, mostly because I want to.
There is a lot of dust where I live, so much so that I literally have stopped washing my bike, by the time I get to the end of my road the bike is LITERALLY filthy again.  Anyway....
The cause of this frustration?  A simple case of dirty points. The pump body houses a coil, that when energized with direct current, induces an electromagnetic field, like a solenoid. This field draws the plunger, one end of which is connected to a diaphragm, in, until on the other side, a lever opens a set of points, or "contacts." I say points because many of you will know I mean.
When the pressure is sufficient so that the diaphragm no longer is able to move, (In other words, when both carb bowls are full, and the needle valves shut off the flow of fuel) the points remain open, and the pump shuts itself off.
What happens when the fuel level gets low in the bowls? The drop in pressure allows the diaphragm to relax, which causes the plunger to retract, and closes the points, which causes a surge of electricity, which draws the diaphragm back in, which increases the fuel pressure again, until the float valves are closed again.
Of course, this may happen 10, 20, 30 times before the pressure is high enough. This is the "clicking" sound you hear when you first turn the key on.  This occurs over and over for as long as the motorcycle is running.  Where am I going with this? Let me explain:
Because of my dusty environment, my points got dirty. Just like points in older vehicles, when dirt gets in there it no longer can make an electrical connection.
So...If the points are unable to fully close because of dirt contamination, the coil inside is not energized again and the pump fails to create pressure.  Please see this picture: I apologize for the quality, my digital camera finally died, all I have is my cell phone.

The fuel pump is assembled and designed very well. I am actually impressed with how solid this pump is.  OK, so what do you do? Whether or not you are having fuel pump problems, I think it would be wise to do the following. It will take you a half an hour and will increase the reliability of your fuel pump exponentially.
Take the left hand side cover off.  Remove the fuel pump rubber from the clips so that it hangs loose. Disconnect the electrical to the fuel pump.
On the side where the wires are connected, (Don't mess with the tabbed side. It is not necessary) remove the single ground screw. Remove the cover.
Look at the pump housing. A mechanical assembly is seen, don't be intimidated. It's really actually very simple. You don't have to adjust anything.  Please note! The tabbed cover is removed in this picture, but it is not necessary OR recommended! We are only dealing with the side of the pump where the electrical is concerned.


Use a rag to thoroughly clean the inside of the cap of all dust.  Using a Q-tip, get the hard to reach areas of the mechanical workings. You want to make sure there isn't any dust or debris that can re-enter the points and cause a fuel pump failure.
Get out some very fine sandpaper, maybe 1,000 grit. Remember, these points are not "User replaceable" so you want to remove as little material as possible. Grab a can of brake cleaner.
Cut some small strips of sandpaper, say 1/4" thick by 4" long, and fold them in half, so that each side includes the abrasive portion of the sandpaper. Open the points with your finger, and let some brake cleaner hit the points, while open. (Watch your eyes!) Then, close the wet points on the sandpaper, and pull the sandpaper out. You shouldn't have to do this more than two or three times.
Get a brand new, clean rag, and after spraying the open points one more time, close them on the rag and pull the rag through. This is necessary because it will clean any debris the sandpaper removed. Do this as many times as it takes to pull out a clean rag, usually 3-5 times. Blow on the open points with compressed air, or give a final spray of brake cleaner to cleanse the points of any fabric debris.
To ensure the points are closing as they should, connect a continuity tester across each point, and measure them when they are together. With an audible continuity tester, you should hear the tone when the points are closed, and silence when they are open.


The tips of the points, where they make contact, actually have a rough, corrugated surface. I assume this is to overcome any debris that may find its way into them? I could be wrong. The individual points are best cleaned with a wire brush. This is ONLY POSSIBLE if the entire assembly has been taken apart in my picture pointing out the dirt.


Do you feel comfortable doing this?? If not, stick to the sandpaper. Your ability to ride the motorcycle depends on whether or not you can get it back together-remember that! There is nearly zero chance of this happening if you just use the sandpaper, but you will not completely "Clean" the contacts, and their grooves.
This is an important step! Before you put it back together, take a small dab of RTV silicone, and either put it around where the cap mates to the body, or after putting the cap back on, use it around the area where the cap seats on the body, after you have cleaned these areas.
Why do this? To seal the cap from dust and moisture. My points were obviously so dirty that they were not closing at all, so the pump never had a chance to energize and activate the diaphragm.
Honestly, whether you ride in the city or like me, in the dirt, I would say this is a worthwhile modification. The pump is designed to be "Serviceable", to a point. Better to do this now, than on the side of the road somewhere!
I am going to complete the gravity feed, because it runs fine with it. But, had I of known this when I was on the side of the road, I would honestly still be using the pump. Either way, it's win-win!

Last Updated on Friday, 05 March 2010 12:54
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