Fuel Return With DCOE Carbs

[cygnusx1]

A finned fuel rail would soak up heat from the engine bay.

[josh817]

A finned fuel rail would soak up heat from the engine bay.

Run some pipe to it from the front to blow air over it... As in like, encase the rail in the pipe. Pipe being that ducting stuff that is wrapped with foil or whatever. Cut holes in the pipe where the barb fittings an poke out from.

[SHO-Z]

I have had my tripples for several years and have never installed them. This thread has me thinking of fabing up a water cooled heat shield bellow them. From my ebay search it looks like a radiator off of a MX bike would be the right size and price and a 12 volt bilge pump to circulate the water. Under the carbs install copper tubing soldered to sheet metal. Heck this will put of installing them again for a while. I would also have a return to the fuel tank on the fuel line with a restriction in it to cause back pressure in the line.

[cygnusx1]

The problem is that the fuel is heating up after it gets into the bowls. Once in the bowls, you have no way of cooling it off.

[bjhines]

The triples are sensitive to heat, most carbs are.

 

Header wrap the exhaust

Make a well fitting multi layered heat shield

use a cold air box(this makes a HUGE difference in consistency in any weather).

Use the stock fuel rail with the stock return restriction(make sure it is clean).

insulate the fuel rail from the hot manifold bolts(later years did this with nylon).

insulate(sleeve/cover) all the fuel lines and rail.

Use a typical carby fuel pump and no regulator.

 

If you want to regulate your system then use ANY fuel pump(EFI or CARBY), and use a return style regulator near the carbys. In this installation you will need to run new lines from the tank of EQUAL SIZE!!!!! for feed and return. DO NOT USE THE SMALLER RETURN LINE! or you will not get the regulation you require.

 

 

 

...

[MREDDLE]

^^OK this is progress... And On the lines I was thinking. I'm sure if I would run the copper vacume line but I like it. So Im looking at venting the under hood temps and containing the exhaust temps with-in the exhaust. This seems easy.

[Lazeum]

I'm not sure to understand clearly what are the options available regarding our fuel setup.

There're 2 types of fuel pressure regulators (FPR): returnless and one with return line.

 

This is all the setup I could come up with those FPR:

 

 

#1 is the setup I currently run. I also run a mech fuel pump between the FPR & the first carb with electrical fuel pump out of the car (R200 mustache bar was on the way). I works quite well with the disadvantages we talked about in the thread.

 

#2 is the same as #1 with the fuel line going back to the tank (with stock lines?). IMO, this sytem would not work since pressure at carbs will not be equal and will not meet 3 psi reqm't.

 

#3 I've moved the FPR after the carbs to keep the pressure up. I don't think it works since pressure on carbs will be the one the fuel pump can produce. Would that works with low pressure fuel pump such as Carter pump?

 

#4 The FPR is having a return line. however, I'm afraid with such a setup pressure with be high after carb pouring up fuel back to them making pressure too high for carbs

 

#5 would work quite well to me but what would be the benefit from #1? It might only help to relief some loads to the pump but would not help for vapor lock.

 

I think I could also have made a 6th version with no restrictor with or without return line based on #1 & #2 setups. What would finnaly work best?

 

I guess the important points are:

- feeding carbs with fuel at any circumptances

- to not overload the pump to keep it reliable and "quiet"

- to avoid head soak & vapor lock

 

 

With the new setup for 2010, I'm probably going to remove or open 100% the restrictor (to keep the gage on top of it to check pressure), plug the return line and use my low pressure Carter pump.

My Exh manifold is ceramic coated, no heat shield under carbs, no thermal protection on fuel hoses.

[Lazeum]

^^OK this is progress... And On the lines I was thinking. I'm sure if I would run the copper vacume line but I like it.

 

It is off topic but the Cannon manifold is having a hollow beam between runners. Would the copper line help to get vacuum more efficiently for brakes?

[josh817]

#3 I've moved the FPR after the carbs to keep the pressure up. I don't think it works since pressure on carbs will be the one the fuel pump can produce. Would that works with low pressure fuel pump such as Carter pump?

A regulator doesn't really do its job unless the gap between regulated pressure and pump pressure is substantial. For instance, If I get a pump that does 4 or 5psi and I want to regulate it to 3psi, it may not work the way you want it. A good Holley pump should put out over 10psi which you can then regulate.

[Lazeum]

That is new to me, adjusting the FPR has some effects on pressure gage readings however.

[josh817]

Yah it had some, but little, effects with me. I think I took out the regulator with my Facet pump, the clicky type and it started to flood even though that pump is 4psi. Put the reg. back in and I was alright. I heard that FPR ♥♥♥♥ from my dad and I believe him for the most part.

[Lazeum]

So basically you're telling us the FPR helped you even if you fuel pump was only rated to 4 psi vs. the regulator at around 3psi? Isn't it contradictory with what you told me on post #29?

[PanzerAce]

Fwiw, #2 is what I'm running basically, except with no regulator on my stock mech fuel pump and triple 44s. Only problem I have is cold starts I have to wait for all the bowls to fill before I can really drive, and *sometimes* I boil the fuel in my bowls on hot days (though I've since re-tuned the engine for a *slightly* higher idle, which seems to have removed that problem, though now I'll get a semi-run-away idle in super hot weather, it'll jump to ~1.5k sometimes in 110 degree heat)

[josh817]

So basically you're telling us the FPR helped you even if you fuel pump was only rated to 4 psi vs. the regulator at around 3psi? Isn't it contradictory with what you told me on post #29?

Yah I'm still not 100% sure. All I know is that those cheap generic Facet pumps that sell for like $25 are not the way to go. They also have pressure surges... A good rotary pump is what we should use...

[Lazeum]

A good rotary pump is what we should use...

 

You mean one like this that whines a lot?

I'll try to quiet it down (not to overload it, good damping with the rest of the body, etc...)

[srgunz]

A regulator doesn't really do its job unless the gap between regulated pressure and pump pressure is substantial. For instance, If I get a pump that does 4 or 5psi and I want to regulate it to 3psi, it may not work the way you want it. A good Holley pump should put out over 10psi which you can then regulate.

 

First of all I do run the factory installed return line for my mikunis. Note this line is smaller than the feed line so it is restricted in that respect.

I run a pump rated 4-5psi and installed a FPR. It ran terrible. I finally removed the requlator and it was perfect. I have measured the psi at each carb and it is just a tad less than 3.5psi. So even with the 4-5psi pump, it actually measures much less than that at the carbs. These were my findings. I do not run any insulation on my fuel lines. I do have the inspection lids louvered as that is my only ventilation from the engine compartment.

[bjhines]

EDIT::: Fuel pump works with the engine running

The factory return system was there to assist with clearing vapors from the lines as close to the carbys as possible. There was no regulation because the various pumps could never over-pressure the system.

 

In a modified system you can do a whole bunch of different things. A return style regulator should be placed as close to the carbys as possible. The return system would work like diagram 5. The lines need to be of equal size so there is no way a monster pump could over-pressurize the system.

[zcarnut]

The factory return system was there to assist with clearing vapors from the lines as close to the carbys as possible. The original electric pump was there to clear the vapors and quit working once the engine started up. The mechanical pump was the only operating pump while the engine was running….

 

Well on the 260Z both the mechanical fuel pump and the electric fuel pump work while the engine is running. During start-up (engine cranking) the electric pump is disabled, although I am puzzled by why the factory did this.

[Buzz]

It seem to me that once the fuel is in the carb it can't come back out into the fuel line,the float closes,why would you need a return? Just to circulate fuel threw the lines? Maybe for vapor lock.if you could flow fuel threw the carb and back out that would make sense for cooling the carbs.I had a return on my webers it didn't seem to make any difference. A heat shield make more sense! Just My 2 cents!!!!

[bjhines]

Z-carnut... If your sytem is not functioning properly then the failure mode is PUMP ON with KEY ON. The early cars had the power connector near the fues box just like the later cars. They often received the electric pump upgrade presale or under warranty until the factory began installing them on every car.

 

APOLOGIES TO ZCARNUT!!!!

EDIT::::This is not correct.::::

That is up for debate as to what various years and service recalls actually did. I traced the circuits on several cars and found that the pump only works when you first turn the key to the ON position, The START position temporarily disables the electric pump. The pump shuts off, and stays off, when the alternator spins fast enough to produce current(engine running).

EDIT:::: This is not correct. I have rechecked and found that the electric fuel pump operates just like the manual says::::

 

 

I have pics from the early 1973 model fitted with SUs, and air injection.

 

The various years had some significant differences on the passenger kick-panel related to wiper delay, auto-wiper with washer fluid button, Watertemp/AIR logic, subfreezing AIR lockout, and possibly a few others. BUT... The same basic operation of the fuel pump remained.

 

 

 

That is not to say you don't need more fuel with major changes. I would consider a more stable, fully regulated system with a full bypass regulator referenced to vacuum. Replumb equal sized lines for feed and return. Place the regulator close to the carbys. This is as stable as it gets and it does it without loading down the pump. You could go to extremes with a PWM controller for your pump too.