Tiny air bubbles on pressure side of fuel pump

[cruzit]

I, recently sold my fj40 to my father in law, which apparently included lifetime warranty on my dime. My problem is according to him that it was hard to start a couple of times. It fires right up after it has been sitting overnight or longer. He said after a short drive he goes to start it within a couple hours and it is hard starting (only happened twice). I ran it (driving and idle) for 1.5 hours and shut it off. Two hours later it fired right up. This is a fresh restoration. New ignition and fuel system. I have never had any problems but who knows. I noticed tiny bubbles in the clear fuel filter between fuel pump and carb, the clear fuel filter before the fuel pump has no bubbles. I disassembled the fuel pump and it looks like it is in perfect shape, all new fuel lines and hose clamps. And no fuel leaking from the fuel pump. There is some bleed down on the fuel line( when I start it it has to pump fuel back up to the carb, does it within few seconds) is this normal? Please help I don't want to spend $ on fuel pump if this is not the problem but it seems if it had a punctured diaphragm it would be leaking. I'm at a loss. Thanks for any input. Appreciate it. Jason. 10-73 FJ40.

 

[DougAustinTx]

I can't really speak to the hard starting, but the only way I can think of for air bubbles to be downstream of the pump, would be if it was sucking air on the suction side. I read where you feel confident in the lines leading up to the pump, but the air has to be coming from somewhere and it isn't going to seep into the line on the pressure side. I would look for an obstruction in the pickup tube in the gas tank to see if the suction line was under so much vacuum that it is letting air in. The only way I can think of to test it would be to blow into the fuel line at the pump end and see if there is something blocking the fuel pickup tube.


If you are seeing small bubbles in the outlet line of the pump, the bubbles should be larger on the vacuum side of the pump (but you say you don't see any bubbles on the inlet side), maybe you are correct that the bubbles are being created inside the pump, but that seems pretty hard to believe, unless the crankcase is pressurized and the diaphragm is ruptured and letting air get into the line that way. I would expect pressurized fuel to be leaking into the crankcase rather than the other way around..... Now that I have mused my way through that whole thing, I realize I haven't helped you much. Sorry. I will finish by saying that a few bubbles in the fuel delivery system would not make the truck hard to start. You can always put a fuel pressure gauge in the line just before the carb and see how the pressures are holding. My '79 has about 3.5 pounds of pressure at idle.

 

[Howard705]

Tiny air bubbles would bleed out in the bowl-it's not under pressure in the bowl. Check the level in the sight glass. You can pull the line and pump off the engine and it will start if the carb is ok. It will run a few minutes. People with modern vehicles consider having to partially hold the throttle or give at a pump or two to be hard starting-I consider it gettng used to the settings of the carb-etc.

 

[Fast Eddy]

People with modern vehicles consider having to partially hold the throttle or give at a pump or two to be hard starting-I consider it gettng used to ... (an old carbureted vehicle)

This ^^^.

The fuel in the lines and in the fuel bowl is probably boiling a bit after shut down. Adding a carb cooling fan may help. It will be worse when the weather warms up.

For the sake of your sanity and your relationship with the father of your spouse, show him this thread.

 

[kruisinkid]

what is the status of your starter motor? is it the old tired stock one?

 

[Pin_Head]

If it isn't leaking fuel to the outside, it isn't a problem.

Hot restarts require proper technique to avoid flooding:

Hold the pedal all the way down but do not pump.
Hit key. When it starts, let up on the pedal.

If you don't have an insulator between the manifold and carb base, fuel may be boiling out of the carb after you shut it off. Take a peek inside for fuel.

 

[cruzit]

Thank you to all you guys for your thoughtful ideas with my fuel problem. The battery and starter are new, seem to work excellent, it does have a carb spacer, perhaps the starting technique will help with the starting problem....and thanks for the advise...I will send him a copy if this thread. Any other ideas are appreciated. I'll keep plugging away.

 

[cruzit]

I can't really speak to the hard starting, but the only way I can think of for air bubbles to be downstream of the pump, would be if it was sucking air on the suction side. I read where you feel confident in the lines leading up to the pump, but the air has to be coming from somewhere and it isn't going to seep into the line on the pressure side. I would look for an obstruction in the pickup tube in the gas tank to see if the suction line was under so much vacuum that it is letting air in. The only way I can think of to test it would be to blow into the fuel line at the pump end and see if there is something blocking the fuel pickup tube. If you are seeing small bubbles in the outlet line of the pump, the bubbles should be larger on the vacuum side of the pump (but you say you don't see any bubbles on the inlet side), maybe you are correct that the bubbles are being created inside the pump, but that seems pretty hard to believe, unless the crankcase is pressurized and the diaphragm is ruptured and letting air get into the line that way. I would expect pressurized fuel to be leaking into the crankcase rather than the other way around..... Now that I have mused my way through that whole thing, I realize I haven't helped you much. Sorry. I will finish by saying that a few bubbles in the fuel delivery system would not make the truck hard to start. You can always put a fuel pressure gauge in the line just before the carb and see how the pressures are holding. My '79 has about 3.5 pounds of pressure at idle.

Impressive engine bay! Nice.