[Stripes]

The holley electric fuel guage reads 8psi on start up cold and rises to about 10 when the sensor warms up. During a vapor lock event the pressure does not drop or change any. I assume the vapor is still at the same pressure as the fuel, but the guage reading doesnt change. After I shut it off a bit, the engine has to turn over a few seconds longer as pressure builds back up and refills the carb.

[Stripes]

Jason, can you send a picture of your set up and which regulator and tank you used? Anyone know if there is such thing as a in tank fuel pump regulated internaly or within the tank to 6 to 8 psi?

I read those HOLLEY fuel pressure sending units for the electric fuel gauges are affected by heat and they show higher pressure as they heat up. Anyone else experience that?

I'm pretty desperate...for a solution. I hate to give up the carb, my other FB is FI, I was trying to stay more stock-ish looking with this one.

[shaker455]

What thermostat and whats the operating temp?
I've have not seen the entire exhaust system wrapped before and not sure your motive of doing so?
Maybe the pipes need to dissipate some of that heat...
Lets see what your engine bay looks like

[dataway]

Before you go too far ... think about this for a moment. If the carb is starved for fuel, the float valve is open, if there is vapor in the line between the pump and the carb it will vent very quickly and the fuel pressure will drop dramatically.

Fuel pumps make very poor air pumps, the float valve and bowl vents should pass the vapor far faster than a pump can maintain it and the fuel pressure should drop dramatically.

If not for the fact that you have changed carbs I would have pointed to an obstruction in the float valve or a plugged bowl vent.

Have you changed or altered the line between the pump and the carb at all?

[Stripes]

Great points. I removed the factory metal line and installed a temp rubber 3/8 hose and saw no change. I then built a metal 3/8 line connected from the RobbMC pump to the new fuel filter that raised the lines running directly off the fuel bowls to see if that would help. No change. I agree it seems like if the carb is running out of fuel, the fuel pressure should drop. When I get it hot next i'll take the carb temp also, and see if the rear bowl still has fuel in it. The Rochester did the exact same thing, hence the carb change searching for an answer. I suspected the crossover was super heating the carb boiling the fuel away, thus the e heads, and blocked heat cross over. 160 thermostat, runs 160-180F, cold case radiator, mechanical oe ac fan.

I wrapped the exhaust for 2 reasons. One, in the summer with the vent on the vent was HOT from the under-hood heat. And I had this issue, so I thought moving the heat out from under the car would heat the fuel lines less. Vent is much improved, dramatically!

I'll go grab a photo.

[dataway]

Not sure if you are running a stock air cleaner with all the bells and whistles ... but if you are, make sure the exhaust intake air preheater valve in the air cleaner is operating properly ... otherwise you'd be sucking hot air off the exhaust manifold ... which would be very hot after extended running. Not saying that would cause a fuel issue ... but just something to look at.

[JLMounce]

Originally Posted by Stripes

Jason, can you send a picture of your set up and which regulator and tank you used? Anyone know if there is such thing as a in tank fuel pump regulated internaly or within the tank to 6 to 8 psi?

I read those HOLLEY fuel pressure sending units for the electric fuel gauges are affected by heat and they show higher pressure as they heat up. Anyone else experience that?

I'm pretty desperate...for a solution. I hate to give up the carb, my other FB is FI, I was trying to stay more stock-ish looking with this one.

Since I went to EFI at the same time, I did not require a regulator as the EFI unit has a regulator on it's fuel rails.

That said, I would run one of these regulators.
https://www.summitracing.com/parts/h...SABEgKQFPD_BwE

And I would look at a retrofit in-tank pump setup such as this.
https://www.tanksinc.com/index.cfm/p...prod/prd84.htm

Here's a quick schematic on how that whole deal would look.



This is probably the most efficient way to put something like that together. It minimizes the amount of tubing you'll need. For the Feed from tank to regulator and from regulator to carb, you should use either high pressure NHRA approved hose or steel/stainless/aluminum, whatever you need if you need it to pass tech. The return line technically could be just typical fuel hose, but you're using such a small quantity that I'd opt to use high pressure fuel hose there as well.

From fuel heat soak standpoint, it may be better to put that regulator nearer to the engine and carb. That would minimize the amount of heat the fuel will absorb, but does also require nearly double the fuel line and adds some complexity to the install.

For the pump I'd use a tried and true Walbro 255 lph pump. More than enough head-room for your engine's power, with enough room to grow in the future. OE level reliability and it's quiet.

[Stripes]

Underhood

[694.1]

Coated manifolds really lower under hood temps. I am thinking something other than VL myself.
Sometimes coils get hot and crap out until cool...Pertronics???

[78w72]

Originally Posted by Stripes

Anyone know if there is such thing as a in tank fuel pump regulated internaly or within the tank to 6 to 8 psi?

I'm pretty desperate...for a solution. I hate to give up the carb, my other FB is FI, I was trying to stay more stock-ish looking with this one.

there are 2 maybe 3 companies offering an intank pump that is internally regulated. aeromotive phantom set ups are a non return line design & supports pretty high power on a carb. might need a regulator to drop down to carb psi but thats easy. you have to cut a hole in your tank & it inserts with a big foam cell for the baffle. theres some videos on their website or youtube. i think holley has a kit too.

[shaker455]

Thanks for posting pics
Do I see a second line coming out of your PCV line?
If so where does that go?
Are you using the Holley sintered filters inside the fuel bowl inlets or did you remove them?
Have you checked and adjusted the fuel bowl levels while engine is running?
How's that spreadbore jetted?
What's your AFR fully warm @ idle, cruise?
I see you said you have a laser gun for IR,
Drive it around to get it to that fully hot point then pull over somewhere & take readings on as much of those un- insulated fuel lines under the hood and the body of that fuel filter you have.
That fuel filter is right inline with all the heat coming off the fan.
I also take readings on the head and radiator hoses upper & lower, thermo gooseneck ,etc.
Let me know what you get

[Stripes]

Well, I'm out driving it. Within a few miles it started sputtering on acceleration, like it was running out of gas. I pulled into a parking lot, pulled the air cleaner, carb was 105f. Radiator 159f, carb, lines cool to touch. Got under the car, the fuel line was around 100 F. Checked the holley, front and rear bowls full. Fuel pressure guage showing 10 pounds and didn't vary. I cant see how its accurate with a stock robbmc pump, it should be about 7psi with the return line. ...

[Stripes]

The afr at idle is 12.7, part throttle cruise is 14.7. I have not gone full throttle long enough to know afr yet. At cruise, when it starts acting up, the af ratio rises to 17, 18, as high as 22. The other black tube is just insulation for the temp sending unit wire. Fuel filter was around 110F. U underhood was not hot. Could the hei pickup coil cause this? Removed the holley sitherned filters. Factory jetted 800 spreadbore. Carb was new in unopened box less than 100 miles ago. I did tune squirtets and accelerator cams, but is preceded any of this. Floats set to just below site plugs. I ran this carb and entire set up on a dyno and it made 500hp, 577tq. Of course, not on my fuel pump.

[shaker455]

If everything is low temp & cold to the touch as well as full bowls it is not a vapor lock issue.
Yes your HEI module could be on it's way out.
If you get a new one make sure to run the proper grease underneath.
You can disconnect the line to carb and crank the car over with line in a gallon water bottle to see how much it pumps after a few seconds.

[Stripes]

Ok, I have a complete new HEI that I will drop in and see if it will change anything. I'm doubtful, since I have changed the coil and module trying to resolve this prior.

[dataway]

Yep, after all you have done I would look elsewhere than the fuel system. Specially with the adequate fuel pressure readings.

I was going to say coil on the first page, but you have HEI .. which I know very little about ... but if you did have a coil ... it would also be classic bad coil behavior ... I've seen tired coils that you could set your watch by with how consistent they start misbehaving.

[shaker455]

Originally Posted by Stripes

Ok, I have a complete new HEI that I will drop in and see if it will change anything. I'm doubtful, since I have changed the coil and module trying to resolve this prior.

Are you running your HEI on a sole 12 volt source rather than the factory points wire?
FYI: 69' model year also has resister wire in the dash as well so check your running voltage

[Stripes]

After all of the above, and with everyones input, I jerked the HEI that had a new car, rotor, module and coil. I dropped in a complete HEI (new everything) only swapping my distributor composite distributor gear for my oil pump, and reset the timing to 12 degrees initial. No carb changes.

Yesterday the car would idle good but wouldn't exceed 20 mph after warm up. With the new distributor, it now runs perfectly. No surging, die-ing out, or lack of fuel feel.

While I will drive it tonight some 40 miles to really test it throughly, it appears that something in the old distributor was bad. And since I had changed the module, cap, rotor and coil; I assume it was the pickup coil. I've never experienced a problem as difficult to track down as this, since it randomly ran really bad, and ran fine at other times.

[dataway]

Excellent! Hope it turns out to be the solution.

Over the years racing motorcycles I have been amazed how utterly consistent ignition components can be when they start to fail. Start the engine up, start a stop watch and the symptoms would appear within seconds of the last time you went from cold to hot.

[steve25]

Just let it be known that you can have good fuel pressure showing up on a gauge but with no where near the volume offlow needed!