Adding a Fuel Regulator with a 32/36

[JumboFett]

Hey y’all,

I’m just toying with the idea of adding a fuel regulator, mostly so I can utilize the excess fuel output as a return line since Webers don’t have any overflow outlets. Is that dumb?

 

Note: I’m sticking with the mechanical fuel pump because it ain’t broke. 
 

Thank you!

[Crashtd420]

5 hours ago, JumboFett said:

Hey y’all,

I’m just toying with the idea of adding a fuel regulator, mostly so I can utilize the excess fuel output as a return line since Webers don’t have any overflow outlets. Is that dumb?

 

Note: I’m sticking with the mechanical fuel pump because it ain’t broke. 
 

Thank you!

No need for a regulator especially with the stock pump..... 

I used a regulator for a while and I'm not a fan of the low pressure ones..

 

What I ended up doing is just using a tee fitting at the carburetor to create a fuel return... I then used a air bleed jet from my carburetor as a restrictor to control the return flow.. 

 

Or you can get the metal y return line from the L20b engine... has the restrictor built into the tubing.  

 

Some might disagree with the next statement but it seemed to work... 

I used a fuel pressure gauge after the tee at the carburetor to make sure the return orifice was a good size... I believe you can adjust the pressure slightly with the size of the return orifice..

 

Side note dont leave the gauge there... I had a bad experience with heat, it caused a failure in the gauge and started leaking fuel on the exhaust causing a fire while I was driving one day.... once set remove and dont think about it... 

[datzenmike]

 

This is the restriction on the L20B return line. It's only large enough to provide a small leak so that cooler fuel from the tank can displace heated fuel from between the pump and the carburetor back to the tank. The resistance allows the pump to push against it and build some pressure. If too large the fuel will simply take the easy way back to the tank and by pass the carburetor. It's not meant to regulate fuel pressure. Fuel pressure is set internally by the fuel pump at 3.0- 3.9 PSI.

[Stoffregen Motorsports]

Yeah, Weber DGVs don't need a regulator or a return if you're using the right pump.

[JumboFett]

53 minutes ago, Stoffregen Motorsports said:

Yeah, Weber DGVs don't need a regulator or a return if you're using the right pump.

Ya, I’m just using the stock OEM pump. If returning fuel isn’t a priority then I probably shouldn’t make more work for myself.

 

1 hour ago, datzenmike said:

 

This is the restriction on the L20B return line. It's only large enough to provide a small leak so that cooler fuel from the tank can displace heated fuel from between the pump and the carburetor back to the tank. The resistance allows the pump to push against it and build some pressure. If too large the fuel will simply take the easy way back to the tank and by pass the carburetor. It's not meant to regulate fuel pressure. Fuel pressure is set internally by the fuel pump at 3.0- 3.9 PSI.

 

I’ll look in my pile of old parts and bits to see if I still have that line. Again, if it’s not super beneficial to return the fuel I won’t worry about it, but just in case it is I’ll look for that line.

[JumboFett]

Thanks for the input, guys!

 

In related news, just in case I do have to upgrade to an electric pump in the future which one would you say is the most reliable, and what pump specs should I look for?

[datzenmike]

2 hours ago, Stoffregen Motorsports said:

Yeah, Weber DGVs don't need a regulator or a return if you're using the right pump.

 

If your vehicle had an L1618 it probably didn't have a return line but all L20Bs do, due to increased under hood temperatures and possible hard restarts from vapor lock in extreme weather. If you have provision for a return line USE it. It's there for a reason and all carburetor engines two liters and larger have it. EFI have a return for the fuel pressure regulator probably on top of keeping the available fuel cooler at the injectors. ZX cars had electric fans to blow cool air on the injectors so it is a problem

[Crashtd420]

1 hour ago, JumboFett said:

Thanks for the input, guys!

 

In related news, just in case I do have to upgrade to an electric pump in the future which one would you say is the most reliable, and what pump specs should I look for?

I have been running a Carter pump for a while, it works but I have never been 100% satisfied....

I believe the facet pump were  recommended by Charlie on here... 

Similar to what the factory uses on the 720s...

 

https://www.pegasusautoracing.com/group.asp?GroupID=FACET

[Stoffregen Motorsports]

Go to Pegasus Racing for the full list of Facet pumps.

 

I've used plenty of Carters, but they are prone to failure and they make a ton of noise.

[datzenmike]

They do make a slight chugging sound I could hear in my 620. The 720 uses rubber grommets for mounting and there is a metal shield around it because of it's exposed position ahead of the rear tire. My 620 was on an '82 720 frame so mounting was the same. Mounting inside the frame near the tank would be better. These make excellent anti theft devices. 

 

 

[JumboFett]

53 minutes ago, datzenmike said:

 

If your vehicle had an L1618 it probably didn't have a return line but all L20Bs do, due to increased under hood temperatures and possible hard restarts from vapor lock in extreme weather. If you have provision for a return line USE it. It's there for a reason and all carburetor engines two liters and larger have it. EFI have a return for the fuel pressure regulator probably on top of keeping the available fuel cooler at the injectors. ZX cars had electric fans to blow cool air on the injectors so it is a problem

Getting back to the fuel return question for a moment, I have this piece (see pics), and it seems to be a check valve of sorts. It was originally connected to my fuel return line, so maybe this is my solution??

[datzenmike]

It's not connected to a fuel return line. The line to the tank is the tank vent.

 

In operation..

 

When engine off any fumes push through the 'flow guide valve' which is what this is, and is sent to the engine crank case and stored. When engine starts intake vacuum draws the stored fumes into the PCV system and burns them. While running and the tank empties, filtered air is drawn back through the vent line to make up the volume removed. Needs a non vented gas cap to work.

[JumboFett]

4 minutes ago, datzenmike said:

It's not connected to a fuel return line. The line to the tank is the tank vent.

 

In operation..

 

When engine off any fumes push through the 'flow guide valve' which is what this is, and is sent to the engine crank case and stored. When engine starts intake vacuum draws the stored fumes into the PCV system and burns them. While running and the tank empties, filtered air is drawn back through the vent line to make up the volume removed. Needs a non vented gas cap to work.

I’ve heard that vent line could be used as a return line. Is that accurate?

[datzenmike]

It can't do both jobs as a return and a vent. If a return, then you would need a vented gas cap or as the tank empties from the fuel pump suction, the tank can implode. Ask me how I know this.

 

 

 

[JumboFett]

22 minutes ago, datzenmike said:

It can't do both jobs as a return and a vent. If a return, then you would need a vented gas cap or as the tank empties from the fuel pump suction, the tank can implode. Ask me how I know this.

 

 

 

Ha! Ok no problem. I can get a vented cap easy. Would that valve still be ok for a check valve, or should I just get a little fitting with a eyelet hole?

[datzenmike]

If using for a fuel return you can't use that flow guide valve. The return line only returns fuel from a fuel system that is return line capable. If you put the fuel lines from an L20B, that would work or like crash 420 did. Know what you are doing. 

[wayno]

You cannot use that line as a fuel return line as is, I believe it goes to a tank somewhere, it is in front of the fender well inside the box on a 521, you need to bypass that tank and run that fume return line straight to the tank.

 

What I did was put a tee in the vent line for the filler tube, that way the fuel went back into the tank that way, but the 620 likely has a hose connection on the tank you can use that the tank uses for the gas fume return, but you are deleting the gas fume assembly.

Edited February 9, 2023 by wayno

[datzenmike]

I think you're right. The early 620s at least had an expansion tank for fumes. My '78 had a flat bed so if there was a tank on the later ones it didn't have it.

[JumboFett]

4 hours ago, datzenmike said:

If using for a fuel return you can't use that flow guide valve. The return line only returns fuel from a fuel system that is return line capable. If you put the fuel lines from an L20B, that would work or like crash 420 did. Know what you are doing. 

Ok! Alternatively, if I manage under hood temperatures with header armor and heat-resistant fuel line sleeving, as well as a cold air intake, might the vapor lock issue be mitigated altogether?

[datzenmike]

Vapor lock is a unique set of circumstances where under hood temperatures rise to the point where gasoline boils in the line or carburetor. Usually after shut down in very hot temperatures. It may not happen at all.

 

Probably what you suggest should do the trick. Most L series have a small heat shield between intake and exhaust and other than the '75-'77 L20Bs the intakes have coolant flow through the runners. The carburetor to intake gasket is rather thick to prevent heat transfer.

[JumboFett]

On 2/9/2023 at 6:39 PM, datzenmike said:

Vapor lock is a unique set of circumstances where under hood temperatures rise to the point where gasoline boils in the line or carburetor. Usually after shut down in very hot temperatures. It may not happen at all.

 

Probably what you suggest should do the trick. Most L series have a small heat shield between intake and exhaust and other than the '75-'77 L20Bs the intakes have coolant flow through the runners. The carburetor to intake gasket is rather thick to prevent heat transfer.

Right on.

 

Re an unrelated matter, do I need to keep the pre-thermostat outlet port on the thermostat housing assembly open and flowing back to the coolant inlet or can I block it off and simply rely on the post-thermostat coolant outlet? 

[datzenmike]

Why would you want to or go to the trouble?? You think you know more about it than the Nissan engineers??? It's function is to prevent cold stagnant water from remaining around the thermostat. Without it the engine relies on convection to warm the thermostat and that is way too slow. Engine over heats while the thermostat hasn't begun to open. The old way had a 'jiggle valve', a small hole in the thermostat to induce some flow but it simply went into the radiator and displaced cold water back out into the engine slowing the warm up. The by pass tube is much better and circulates this partly warmed coolant directly back into the engine speeding the warm up. There's not much you can do to improve the L series. In many cases removing or altering things can harm mileage, performance and engine life.

[JumboFett]

47 minutes ago, datzenmike said:

Why would you want to or go to the trouble?? You think you know more about it than the Nissan engineers??? It's function is to prevent cold stagnant water from remaining around the thermostat. Without it the engine relies on convection to warm the thermostat and that is way too slow. Engine over heats while the thermostat hasn't begun to open. The old way had a 'jiggle valve', a small hole in the thermostat to induce some flow but it simply went into the radiator and displaced cold water back out into the engine slowing the warm up. The by pass tube is much better and circulates this partly warmed coolant directly back into the engine speeding the warm up. There's not much you can do to improve the L series. In many cases removing or altering things can harm mileage, performance and engine life.

I’m definitely not trying to outsmart the engineers of yore, I’m trying to avoid backtracking because I unknowingly blocked off the bypass inlet on the inlet water neck and I just wanna be certain I need to correct the oversight. 

[Stoffregen Motorsports]

So I had an issue a couple years ago with rising temps at idle on LS3 engines I use in my swaps. The temp would increase at idle only. Even 100 rpms over idle and you could see the temps come down rapidly. I spoke with GM engineers, GM techs, and a handful of tuners and mechanics. It got so bad on one LS3 that I almost pulled it for warranty.

 

Cut to the chase - it was a bad combination of heater valves and engine cooling paths. The GM requires that coolant circulate around the t-stat to prevent cavitating at the t-stat. Regular old heater valves that open and close do not provide this re-circulation, while modern 4-way heater valves do. The cavitation which occurred at the t-stat gave inaccurate temp readings to the t-stat itself and would cause it to stay closed longer. In a moment of inspiration, I disconnected the heater hoses and installed a short bypass hose. Problem cured. Side note - none of the experts were able to figure this out.

 

So long and short of it - I have been re-thinking all of those old tricks. Blocking off the bypass on a Datsun L motor used to be par for the course. It would be a neat experiment to see how the bypass affects the t-stat or overall engine temps in specific ranges.

 

This also has me thinking of heater delete. Old school race motors have a plug installed in the rear of the cylinder head, and at the inlet on the side of the timing cover. Would a bypass there help or hurt? It is commonly agreed upon that installing a bypass there would hurt the engine's coolant circulation path. Yet on BMC race engines, I always see the rear cylinder head heater port going to a header tank. Apples to oranges, maybe, but interesting nonetheless.

[JumboFett]

41 minutes ago, Stoffregen Motorsports said:

So I had an issue a couple years ago with rising temps at idle on LS3 engines I use in my swaps. The temp would increase at idle only. Even 100 rpms over idle and you could see the temps come down rapidly. I spoke with GM engineers, GM techs, and a handful of tuners and mechanics. It got so bad on one LS3 that I almost pulled it for warranty.

 

Cut to the chase - it was a bad combination of heater valves and engine cooling paths. The GM requires that coolant circulate around the t-stat to prevent cavitating at the t-stat. Regular old heater valves that open and close do not provide this re-circulation, while modern 4-way heater valves do. The cavitation which occurred at the t-stat gave inaccurate temp readings to the t-stat itself and would cause it to stay closed longer. In a moment of inspiration, I disconnected the heater hoses and installed a short bypass hose. Problem cured. Side note - none of the experts were able to figure this out.

 

So long and short of it - I have been re-thinking all of those old tricks. Blocking off the bypass on a Datsun L motor used to be par for the course. It would be a neat experiment to see how the bypass affects the t-stat or overall engine temps in specific ranges.

 

This also has me thinking of heater delete. Old school race motors have a plug installed in the rear of the cylinder head, and at the inlet on the side of the timing cover. Would a bypass there help or hurt? It is commonly agreed upon that installing a bypass there would hurt the engine's coolant circulation path. Yet on BMC race engines, I always see the rear cylinder head heater port going to a header tank. Apples to oranges, maybe, but interesting nonetheless.

Thank you! The plan is definitely to reintroduce the heater once I get the entire system reconditioned, but for now I’ve blocked off the port in the rear of the cylinder head and at the inlet neck. I’m going to reintroduce the bypass tube today as I continue to chip away at putting everything back together. Yesterday was dedicated to fitting a fat 3-core aluminum radiator; some slight core support cutting was necessary, but I kept it very minimal.