Vapor lock driving me crazy

[68charger440]

I have been fighting vapor lock for quite some time on the real hot days.  I can watch the fuel boil in the glass fuel filter and the sight glasses on the carb don't show any fuel once it happens, so I am very confident that it is vapor lock.  The temp gauge runs at 180 or so, so that is fine.
I have the valley pan with the blocked off heat crossover installed
I installed a 1" phenolic carb spacer
I have rerouted the fuel lines away from all heat sources
I am at roughly 5500 foot elevation, so the gas boils real easy up here.
I have the carter high volume mechanical fuel pump, but the stock one does it too.
I could install an electric fuel pump, but then the noise and vibration might make me shoot myself.
The motor is:
440 bored 40 over with a balanced 500 inch stroker kit installed
Stock fresh 906 heads. 
10.52 static compression.
edelbrock performer rpm intake
Edelbrock performer cam
Proform 850 dp
Stock converter
3.91 sure grip
18 initial timing 34 total
3" exhaust all the way back from the headers with an X pipe in the middle
MSD ignition
I have heard that the fuel vapor separator may help, but that there used to be some that were made incorrectly.  Has that been corrected, and if so who has the good ones, or are they all good now?
Does anyone know of anything else to try to fix this?
Thx
Jim

[cdr]

you will need a fuel return set up  this is the regulator i used on mine, it is for a mechanical fuel pump. mount it up right before the line splits to the front & rear carb bowls & then run a return line to the tank off the regulator

http://www.summitracing.com/parts/qft-30-899/overview/

[68charger440]

So I can't use the vapor seperator with my mechanical fuel pump without a regulator?

[cdr]

So I can't use the vapor seperator with my mechanical fuel pump without a regulator?

you can try it, but there is a lot of line up to the carb exposed to a lot of heat.   mine works very well & i have been in over108 deg, my car is 512ci & ac. runs cool & no vapor lock.

[firefighter3931]

Hey Jim,

The return regulator that Charlie posted is the best option. Keep the fuel circulating to prevent vapor lock. Not a fan of those vapor seperators 

The fuel they sell at the pumps these days is terrible for carbureted applications. It's formulated for high pressure fuel injection and doesn't tolerate low pressure and heat very well 


Ron

[68charger440]

Sorry to be thick headed, but help me to understand...
1. I have always heard that an electric fuel pump will eliminate vapor lock because it pushes instead of pulls the fuel, and I guess that pushes the vapor out through the carb. Is that correct?
2. Does vapor lock on our old cars occur at the fuel pump, at that is why the pump can't pull the fuel? So if that same mechanical pump were in the back of the car, then it would act just like the electric pump and you would never get vapor lock unless the fuel somehow boiled to vapor in the back of the car?
3. If point 2 is true then wouldn't the regulator be too far downstream at the carb, since the vapor lock itself would begin at the pump before the regulator, and in that case the mechanical pump would still not be able to pull the fuel since it is trying to pull vapor still?

I probably didn't do a very good job of expressing my confusion as to how this would work.

[68charger440]

...and if all of the above is true then wouldn't the vapor seperator keep a cool flow of gas going through the mechanical fuel pump thereby keeping the pump from ever vapor locking to begin with, and then it would be able to push the vapor further down toward the carb out through the carb just like the electric fuel pump?

[cdr]

the heat in the fuel system ads up, from back to front it gets hotter & hotter, bleed off the hottest boiling fuel & it cools as it goes to the back. a electric pump will not help much if any on boiling fuel,, a return as close to the carb is what works.

[firefighter3931]

As noted above by CDR the main issue is lack of circulation. An electric pump can cause the same issues if it is run as a dead head system. Stock...these cars were basicly dead-head design fuel systems with no return line to the tank...only a simple vapor separator which is not as effective as a bypass regulator which keeps the fuel moving front to back. This circulation cools the fuel temps down and helps to suppress vapors and fuel boiling.

The basics of fuel ; Gasoline has a boiling point and flashpoint where it will ignite. As it gets warmer it produces more vapor which converts it from liquid to a gaseous state (vapor) and that is what causes the problem. Keep in mind that the fuel that these fuel delivery systems were built around are completely different from the current fuel formulations we have at the pumps today. The current fuels are more heat sensitive due to the additive packages and ethanol.

The "old" gas could sit static in the fuel line for a longer period before turning into vapor so having the fuel system cycle the fuel front to back was not a requirement for reliable performance. Today's fuel is formulated for todays engines which run high pressure fuel injection with return fuel systems....vapor lock is a non issue with new cars for this reason. 

Mechanical fuel pumps are attached to a hot engine so running fuel through a mechanical pump only aggravates the problem. Having the fuel circulate will reduce the fuel temps and prevent the problem from occurring in the first place.

Circulation is the key 



Ron

[c00nhunterjoe]

Dont forget cavitation. Not really an issue on stockers but when people convert to electric and stick a 140 gph pump on the stock 5/16 lines......  it never ends well and they cant figure out why they still have issues.

[six-tee-nine]

And for the guys without a return line, should we fab something or are there parts available to convert?

[Tom Q]

Come on now, figure out what is broke. Engage the brain.

How hot is it under the hood? Measure the temp and get back to us.
Go to the home store and get a barbecue thermometer and mount it in front of the carb.

Insulate the fuel line [rubber hose cut down the middle] that runs along the frame rail. Be sure to be using metal lines from the fuel filter to the carb. Use a metal fuel filter. Is your fuel pump weak or fp pushrod too short?
Use the  Carter street pump

BTW 180 is too low of a min operating temp, 195 for today's fuel. But you guys seem to know more than me so just keep thinking 1970's

[1974dodgecharger]

Come on now, figure out what is broke. Engage the brain.

How hot is it under the hood? Measure the temp and get back to us.
Go to the home store and get a barbecue thermometer and mount it in front of the carb.

Insulate the fuel line [rubber hose cut down the middle] that runs along the frame rail. Be sure to be using metal lines from the fuel filter to the carb. Use a metal fuel filter. Is your fuel pump weak or fp pushrod too short?
Use the  Carter street pump

BTW 180 is too low of a min operating temp, 195 for today's fuel. But you guys seem to know more than me so just keep thinking 1970's

do you go in every thread and repeat the same thing over 

[cdr]

And for the guys without a return line, should we fab something or are there parts available to convert?

when i replaced my factory line from the tank to the pump I bought two 3/8 prebent lines & ran them next to each other.

[303 Mopar]

And for the guys without a return line, should we fab something or are there parts available to convert?

when i replaced my factory line from the tank to the pump I bought two 3/8 prebent lines & ran them next to each other.

  You will also need a new sending unit with a return.  Call Dave at Roseville and he will hook you up with the line and sending unit.  (http://www.rosevillemoparts.com/product_info.php/p/fuel-tank-sending-unit-68-70-b-body-3-8-with-return/products_id/8426)

I left my 5/16" line in and made that my return while installing a new 3/8" main line.  The pre-bent lines fit nice, and I just drilled a second hole in the frame rail.

[myk]

Come on now, figure out what is broke. Engage the brain.

How hot is it under the hood? Measure the temp and get back to us.
Go to the home store and get a barbecue thermometer and mount it in front of the carb.

Insulate the fuel line [rubber hose cut down the middle] that runs along the frame rail. Be sure to be using metal lines from the fuel filter to the carb. Use a metal fuel filter. Is your fuel pump weak or fp pushrod too short?
Use the  Carter street pump

BTW 180 is too low of a min operating temp, 195 for today's fuel. But you guys seem to know more than me so just keep thinking 1970's

He can't figure it out, that's why he's here, and we're here to help.  Sorry that we're not all ASE Master Certified Techs with a degree in snobbery like you are....

[68charger440]

Well, I guess I have some plumbing work to do.   I sure will miss the clean look of a single fuel line going into the chrome fuel line feeding the carb.  
I guess where my thinking was wrong above it that maybe the vapor separator doesn't keep a constant flow of cool fuel running through the pump.
The logic in my brain still thinks that if the pump is cooled down then it would not vapor lock and be able to push the vapor out through the lines above it through the carb, but you guys haven't steered me wrong yet, so I'll go with it.
Jim 

[68charger440]

I left my 5/16" line in and made that my return while installing a new 3/8" main line.
[/quote]

I think that is what I will do too.
At what point should I consider 1/2" fuel line?  Is 600 hp roughly the cutoff point for that upgrade?

[firefighter3931]

Lots of guys run 3/8 line pushing in excess of 600hp so you're good to go Jim. A 3/8 supply line is fine for your application 

On a side note ; My old 446 making 535hp/540tq used the 120gph carter street pump with a single supply line and no return....dead head system. I used a metal fuel filter on the discharge side of the pump with braided fuel line up to the carb. I insulated the braided line with a chunk of conduit that was thermally protected and had no issues with vapor lock. Was it as good as a return system....definitely not, but it worked for me. We don't get as hot up here in the great white north so that probably helped a bit as well but I did drive it on several 100* days testing the cooling and fuel systems and never had a problem. 

This might be worth a shot before re-plumbing the fuel system 

This is the insulating conduit I used from DEI :

http://www.summitracing.com/parts/dei-010414/overview/




Ron

[68charger440]

Lots of guys run 3/8 line pushing in excess of 600hp so you're good to go Jim. A 3/8 supply line is fine for your application 

On a side note ; My old 446 making 535hp/540tq used the 120gph carter street pump with a single supply line and no return....dead head system. I used a metal fuel filter on the discharge side of the pump with braided fuel line up to the carb. I insulated the braided line with a chunk of conduit that was thermally protected and had no issues with vapor lock. Was it as good as a return system....definitely not, but it worked for me. We don't get as hot up here in the great white north so that probably helped a bit as well but I did drive it on several 100* days testing the cooling and fuel systems and never had a problem. 

This might be worth a shot before re-plumbing the fuel system 

This is the insulating conduit I used from DEI :

http://www.summitracing.com/parts/dei-010414/overview/




Ron

I think I will give that a try before replumbing.
I found this Holley regulator in my  garage. It has no signs of ever being used, but I can't for the life of me remember where I got it. Besides the blue caps it has blue paint on the adjuster threads.  Can anyone tell me if this is the right one for a carb application? Fittings are 3/8.

[cdr]

if no # on it  ?? I doubt it's one for a return , one for a return are made different inside.the one you need has a screw in jet.

[68charger440]

if no # on it  ?? I doubt it's one for a return , one for a return are made different inside.the one you need has a screw in jet.

Scratch the 3/8 fittings it is larger, probably 1/2. 
Anyway, the screw in jet?  Is that different from the hex key pressure adjuster on top?  Where is that located?

[68charger440]

There are no numbers on it.  Here is a better pic.

[68charger440]

Here are a couple more good pics. The second one is looking in from the bottom.

[six-tee-nine]

Thanks for all the tips... just to make sure I do it right the first time when I buy fuel lines and acommodating parts in the near future.