Fuel System Not Holding Prime - Help!

Really scratching my head trying to figure out why my fuel system isn't holding prime once I get it running. I'm working on my '66 Cj5 w/ dauntless v6 and have been trying to locate the source of this problem for quite a while.

So far I have had the carburetor totally rebuilt with all new seals and gaskets, and I've replaced all my fuel lines. If I pour a half shot of gas into the carb I can get it going, and it'll sit there and run all day long, but when I turn it off the fuel falls right back through my glass filter between the pump and the carb and then I can't get it cranked again. There is no gas leaking out onto the ground anywhere. Any ideas? Any help here is greatly appreciated.

 

just a guess . try it with gas cap loose or off

 

I'm not familiar with the V6, but the check-valves in the fuel pump itself should prevent what you describe. And it should prime itself if they are working.

Also be sure that a bad pump diaphragm has not been leaking fuel into the oil pan.

Rebuild or replace the pump.

 

Had that problem, gas was leaking from the fuel line, where the vinyl line attached to the metal line. Gas was spraying on the hot engine block and it evaporated and no leak showed up. I think Focker had this problem too. He did a thread on it.

 

Cheap fuel pumps will not hold a prime. Had this problem with my chevy. I put a good one on it and no more problem.

 

I run an electric pump in line with the mechanical. Electric pump has a switch to cut off once cranked and prime picks up

 

Makes me think your fuel pump diaphragm is weak but not torn since you dont mentions gas in the oil.

 

X2 on the pair of check valves in the fuel pump. It could be as simple as a piece of crud caught in the seat.
-Donny

 

Think you have more than one problem. Fuel draining back out of fuel line is due to defective fuel pump. No fuel in carb is something else. The carb inlet is at the top of the bowl and cannot siphon fuel out of the bowl.

 

I haven't checked the oil but will today. That sounds serious, would it just take a simple oil change to get it out? What kind of damage could that create?

 

1-carb should hold enough fuel to start back up ,at least 2-3 days after shutoff.
2- I had the no fuel in line problem once, small cracks in fuel line that would
let air suck in, but would not let any fuel leak out, because it was a suction line,
no pressure to push out fuel.
3- agree with others,about bad pumps,some don't hold a prime?

 

Eventually? Low oil pressure and a wrecked engine.

 

Update: I dropped the oil out and there's definitely gas in it. I'm ordering a new fuel pump now and I'd like to get some input, these two pumps look to be identical but there's a big price difference. Is there a quality difference?

New Replacement Fuel Pump (single action) Fits 65-66 CJ-5, Jeepster with V6-225 engine

vs

Spectra Premium Fuel Pump A1083MP


One more question, will fresh oil be good enough or should I run some fresh oil through it, dump it, and then put more fresh oil in it?

 

Rockauto has 3 different brands in 20-25 range. Unless Kaiser-Willys has some secret American made source, they just reselling the same stuff.

 

this

 

Now that you have a pump coming you can just drain the oil and replace the filter. Should be fine to just do that no need to drain again if you leave the filler cap off and the drain plug off while you wait on the fuel pump shipment - should all evaporate pretty quickly leaving those openings.

 

Don't wanna hijack this post but I'm having a similar situation. Mine also has a electronic pump as well as the one on the block. Don't start for a few days and the jeep doesn't want to start .... replaced all the fuel filters.

 

Chrisg it would be better for you to start your own post. It sometimes gets confusing when repair suggestions are acted on by the wrong poster.

 

Thanks walt... just reading this and will do..

Chris