Fuel pressure and vapor breaker

[Sonny]

I added a vapor breaker fuel filter to my 440 and my fuel pressure dropped from 6 to 2. Car seems to run fine, although the carb float level is now at the bottom of the site glass. Is 2 psi (at idle, can’t see the gauge while driving) a problem and is that normal with a vapor breaker? I’m running a stock mechanical pump.

 

[steve340]

2 psi is to low. I would check the rate of return back to the tank it sounds like it will be to much from what you have written in your post.
You may need to close the return orifice.

 

[Sonny]

2 psi is to low. I would check the rate of return back to the tank it sounds like it will be to much from what you have written in your post.
You may need to close the return orifice.

Thought about adding a 1/4” ball valve and “regulating” the vapor line flow to the tank as well.

 

[steve340]

That would work but it is another place for a fuel leak to occur.
I would put a clamp on a flexible part of the return line not as a fix but a test to see if the fuel pressure jumps up.

 

[PurpleBeeper]

steve340 has a good idea & I think he's right. "Something" I heard about the factory-style vapor separators was to have the return orifice .020" (? or something like that ?).

I've been planning to put in a return line similar to what you're doing with the fuel filters with the extra little nipple. My plan (un-tested) was to run a 1/4" return hard line & somewhere in the flexible hose section:
a. cut the rubber 1/4" hose
b. take a piece of 1/4" rod stock & drill a .020" (?) hole through it lengthwise
c. put that rod w/hole inside the hose where I made the cut
d. clamp both sides of where I put that rod w/hole in

As I said, that's my plan, though I haven't done it yet. Maybe something like that would help you? Steve340's idea to "test" if it would work by restricting the return line is a good one to see if the idea is good before you start modifying stuff.

 

[steve340]

The standard orifice is 0.060"
This does seem rather big. That is give or take 1.5 mm hole.
The standard vapour separator is not a filter at all it is really a sort of air bleed.

 

[lewtot184]

the aftermarket vapor seperators have too large of a return orifice. I clean the paint off the return nipple and soft solder it up; then re-drill to around .030". these are filters as well as vapor return. too large of a return orifice will definitely bleed off too much pressure.

 

[Sonny]

The standard orifice is 0.060"
This does seem rather big. That is give or take 1.5 mm hole.
The standard vapour separator is not a filter at all it is really a sort of air bleed.

I think I’ll order a mopar standard vapor breaker and see if it operates better.

 

[Sonny]

That would work but it is another place for a fuel leak to occur.
I would put a clamp on a flexible part of the return line not as a fix but a test to see if the fuel pressure jumps up.

I tried that with vice grips and it increased the pressure.

 

[Sonny]

Here is a replacement VB on eBay. The 1/4” hole is reduced to a 0.060” hole. Mystery solved!

 

[Sonny]

the aftermarket vapor seperators have too large of a return orifice. I clean the paint off the return nipple and soft solder it up; then re-drill to around .030". these are filters as well as vapor return. too large of a return orifice will definitely bleed off too much pressure.

You were correct!! Thanks!

 

[lewtot184]

those vapor seperators were used with HP440's and hemi's. both had high pressure pumps (8-9psi) vs the non HP big blocks (3-5psi). the .060" return or larger doesn't work well with 3-5psi pumps. they will drive fine with 6psi pumps but are a power loss. reducing the size of the return with 6-7lb pumps has worked well for me.

 

[Sonny]

For those of you that use the separator, do you also use an additional filter? Box says the separator has a screen in it but not sure it’s enough?

I’m swapping to a 3/8” supply line, high perf pump, and adding the stock separator.

 

[lewtot184]

For those of you that use the separator, do you also use an additional filter? Box says the separator has a screen in it but not sure it’s enough?

I’m swapping to a 3/8” supply line, high perf pump, and adding the stock separator.

you don't need a filter between the separator and the carb. the separator is a filter. don't put a filter on the suction side of the pump either.

 

[Sonny]

One last question. I took this pic from an episode of graveyard carz last week of the separator. Does someone sell that 5/16” fuel pump output hard line? My spectra hp fuel pump has the same orientation, but the threads are 1/8” npt and there is an inverted flare on the inside.

 

[lewtot184]

View attachment 732984 One last question. I took this pic from an episode of graveyard carz last week of the separator. Does someone sell that 5/16” fuel pump output hard line? My spectra hp fuel pump has the same orientation, but the threads are 1/8” npt and there is an inverted flare on the inside.

you can get those fittings at any parts store that sells brass fittings. 5/16" female inverted flare with 1/8" male pipe threads.

 

[Sonny]

you can get those fittings at any parts store that sells brass fittings. 5/16" female inverted flare with 1/8" male pipe threads.

When I look into the hole, the flare (pointed part) points into the pump (away from the fitting) like in needs a male flare adapter to go in there first.?

 

[steve340]

Post a pic of your pump. Stock they normally use a parallel thread and a double flare on the pipe.
By the way NPT is a tapered thread that is designed to lock and seal on the threads alone.
I have seen it on aftermarket pumps and in that case you would use an adaptor fitting to convert to a pipe/nut style fitting.
They should be easy to get. That steel tubing is called Bundy tubing.

 

[Sonny]

Post a pic of your pump. Stock they normally use a parallel thread and a double flare on the pipe.
By the way NPT is a tapered thread that is designed to lock and seal on the threads alone.
I have seen it on aftermarket pumps and in that case you would use an adaptor fitting to convert to a pipe/nut style fitting.
They should be easy to get. That steel tubing is called Bundy tubing.

 

[steve340]

It is a bit hard to see. It looks too fine a thread and no taper to be NPT but not sure. I cannot identify that thread but I suggest you do. Once you identify the thread you have something to work with.
I think that taper at the bottom of the threads may not be a seat but is from the drill used when the fitting was threaded/manufactured.
That pump would need the adaptor fitting in my opinion.