4104 fuel line question?

[5B Steve]

  Hello,

  I have a question, Larry P's' 4104 (1960) isn't getting any fuel. Put a temporary fuel line from the tank to the filter.

  Engine will run when both filter's are full. Is there a way you can drop a line from the pump to a bucket of fuel

  and see if there is a problem, and what size line would it take ID wise?

   Steve 5B.......

 

[luvrbus]

Drop the 3/8 in fuel line from the primary filter to the bucket doesn't the 4104 have a fuel strainer also ?

[Len Silva]

I wouldn't do it directly from the pump unless you use an external filter.  Connect a 3/8" line from the primary filter intake (after the check valve) and drop it in the bucket. Also connect a line from the return on the engine and drop it into the bucket as well.

Once you get the engine running, watch for air bubbles in the return, it should be completely clear.

After you have established that the engine runs well with no air in the return, connect the supply back to the tank but leave the return in the bucket.  If you continue to get bubbles, you have a suction leak in the supply.

[gus]

About what Len says except I would pump from the end of the disconnected tank supply line so the whole supply system is checked at once.

This is a little more work but it checks the whole system. If the supply line has a hole anywhere before the pump a small electric pump here will cause fuel to leak from the line.

The check valve at the primary filter may be stuck closed, or stuck open. If it is closed no fuel will flow. If open it will suck air and prime will be lost when the engine is off and thus no flow when connected for normal operation.

Also, as Len says, don't bypass the filters- that may cause injector clogging!



It the supply line has a leak anywhere before the pump it will suck air and empty the primary filter. A leak after the pump and before the secondary will cause fuel to spurt out.

[5B Steve]

  Good evening,

   Here is what we found out, Last fall I installed a temporary fuel line from the elbow on top of the tank to the

   first filter, on the outside of the bus. Filled both filters and it would run for about 20-30 minutes, however under

a load  it would suck them dry. Thought it was the pump, not to be, so today I removed the line on the top of the

tank and put it in a clear bottle to see if the pump would suck the fuel. Worked fine, and you could hear the fuel

return to the tank. So here is what I did, took the line shoved it down the neck of the tank and it ran fine till I got

the bus to where I needed it to be.  Question is, is it possible that on the inside of the tank below the elbow

something has failed in the tank or is there a tube or line that has disconnected?

Steve 5B......

   

[Len Silva]

That is quite possible, even likely.

Pulling the tank is a pain but may be necessary.  Depending on the level of finish in your conversion, you may be able to cut a hole in the floor above the tank and lift out the entire assembly where the lines drop into the tank. That would be the time to add a fuel gauge sender as well.  That would be the easiest if it's possible for you.

[Scott Crosby]

I had a problem this week there my GM bus was running out of fuel with 40-60 gallons still in the tank.  We think the problem was the pickup tube in the tank.  We swapped it to another tube that was mounted in my tank.  It's running good, but there is still 75 gallons in the tank.  I'll know later today after a 400 mile run. 

Suspected hole and crack in the pick up tube near the top 1/3 of the tank.

[gus]

What you have done is eliminate all of the fuel supply system as the problem except the pickup tube in the tank!

Before you do anything else blow into the tank supply feed tube with shop air where the supply line connects to the tank top.

This will clear out any gunk blocking the tank pickup tube.