Replace Fuel Pump?

[Donvito]

I have been dealing with an intermittent fuel pump problem for the past year. I thought I had it fixed several times but it continues to appear. The problem happened four times on a 1,500 mile trip last week, twice at start up and twice while riding at about 75 mph on an interstate resulting in a stall.

 

Since I thought the problem was located in the ignition circuit, I had a jumper wire ready to attach to my terminal block which worked initially but even that wound up failing. When it wouldn't start one morning when the gas tank was low, I had to pour a couple of gallons of gas in and the pump began working again. It seems like the level in the tank has an effect on the fuel pump and it is more likely to fail when the level is low.

 

When I got home, I tested the pump by pumping into a gas can. The tank had about two gallons in it. I ran the pump it through the relay, through the ignition system but bypassing the relay and directly from the battery and the pump failed in all scenarios. So, I thought the problem may be a restricted fuel supply to the pump so I drained the tank, cleaned the petcock and replaced the fuel filter. After doing this, I ran it through a bunch of tests and the pump didn't fail.

 

While working on the tank, I tried to operate the pump with the petcock closed and this resulted in the same condition as when the pump fails. This condition is a drop in voltage to about 10 volts and the relay buzzes and vibrates. This is the same problem for the last year but I think I have it narrowed down to a bad pump or a restricted fuel supply.

 

So, has anyone experienced pump failure from restricted fuel supply resulting from a dirty fuel filter or dirty petcock screens? What should the pump do if it is operated with the petcock closed? Should the voltage drop?

 

I have read about similar failures in 2nd Gen. bike's fuel pumps but not very common in 1st Gen. Is there a way to test the fuel pump or should I rebuild it or replace it? Pumps for 1st Gen. are pretty scarce so will a pump for a 2nd Gen work?

 

I have searched many times for answers but I apologize if I missed one. Thanks for your help.

[Prairiehammer]

There has been one instance of one of the poppet valves in the First Gen fuel pump becoming misplaced or cocked, thus preventing it's proper operation. There are two of these valves. One is opened on the intake stroke of the pump armature while the other is closed. When the discharge stroke happens that first valve closes and the other opens. If one or the other fails to open or close properly, the pump does not 'pump'.

As in the Second Gen fuel pump, the points may be sticking and/or burnt, causing intermittent operation.

The 'roll-over valve' (check valve in the tank vent) may be malfunctioning (stuck closed) or the tank vent line may be otherwise obstructed, preventing proper venting of the fuel tank. As fuel is drawn out of the tank and air is prevented from entering the tank, a vacuum is formed, impeding the pump from getting fuel to pump to the carbs.

[flyday58]

While working on the tank, I tried to operate the pump with the petcock closed and this resulted in the same condition as when the pump fails. This condition is a drop in voltage to about 10 volts and the relay buzzes and vibrates. This is the same problem for the last year but I think I have it narrowed down to a bad pump or a restricted fuel supply.

 

So, has anyone experienced pump failure from restricted fuel supply resulting from a dirty fuel filter or dirty petcock screens? What should the pump do if it is operated with the petcock closed? Should the voltage drop?

Hey Vee, these are the exact symptoms I had when my points went bad on the fuel pump. Unfortunately the points I got off ebay, while they were exactly the same as my pump's, refused to work. The gap was not right and no matter how I bent the tangs to adjust them, it would fail after reassembly, although they worked great before reinstalling the plastic cover. I put my original points back in and it's been working ever since, go figure.

 

The points would stay together in the original scenario, resulting in the battery dropping to 10 volts. Since they weren't opening and closing, no fuel was being pumped. And after about three seconds the fuel relay cut power to the pump, so no fuel was ever gonna get through.

If you decide to try points, Dingy has this excellent tech article, with pics, explaining fuel pump ops and showing great views of the pump taken apart. I used it.

Fuel pump operation

[Patch]

 

"Since I thought the problem was located in the ignition circuit, I had a jumper wire ready to attach to my terminal block which worked initially but even that wound up failing. When it wouldn't start one morning when the gas tank was low, I had to pour a couple of gallons of gas in and the pump began working again. It seems like the level in the tank has an effect on the fuel pump and it is more likely to fail when the level is low. "

 

THIS sounds like the pump! Pumping systems work "in simple terms" by lifting or moving weight, when you add gas you add weight, this means you add pressure to the _in_ side of the pump. So Pairiehammer suggestion makes good sense.

 

"When I got home, I tested the pump by pumping into a gas can. The tank had about two gallons in it. I ran the pump it through the relay, through the ignition system but bypassing the relay and directly from the battery and the pump failed in all scenarios. So, I thought the problem may be a restricted fuel supply to the pump so I drained the tank, cleaned the petcock and replaced the fuel filter. After doing this, I ran it through a bunch of tests and the pump didn't fail.

 

While working on the tank, I tried to operate the pump with the petcock closed and this resulted in the same condition as when the pump fails."

 

AGAIN I would say the pump.

This condition is a drop in voltage to about 10 volts and the relay buzzes and vibrates. This is the same problem for the last year but I think I have it narrowed down to a bad pump or a restricted fuel supply.

 

This may be the result of a couple things, if the pressure builds the contacts want to switch to off, if the valve is jerky, the drop is quick and the contacts want to open. So for me what this means is, that both have a problem, likely the problem started with the pump and the relay has overheated! Inline with flyday description.

 

 

When you measure voltage for a circuit it is best know the voltage before, during and after test's, that is voltage in voltage through and out to ground.

 

I would clean the contacts with "contact cleaner" and use a fine emery cloth between the contacts, You don't want to remove good material, you want to remove the carbon causing the resistance/V loss, which is likely why the you are measuring 10 volts. You will likely see some improvement right away, providing the relay coils are OK? But I would either replace or service the pump, at the very least an inspection of the working parts.

 

Patch

[Karaboo]

Consider a point file for the contacts, if one is available.

[Donvito]

Thanks for all the great advice. I will open the pump and clean the points to see if that solves the problem. If not, I'll be looking for a new pump. Thanks again.