bianchini

Simplifying fuel delivery and return

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Hi all, 

 

I have been doing some reading on the fuel system and I am still a little confused on the "best" configuration for the fuel delivery and fuel return. Since we can modify 2002s much more with products and emissions equipment now no longer required, I wanted to figure out what is a cleaner/ simpler setup... 

 

Current configuration: 

-74 2002

-M10

-32/36 Manual choke carb

-stock fuel configuration WITH return line (photo attached of setup) 

-no smog equipment (all removed)

-daily driver

 

Questions: 

- can I plug the return line? 

- if yes, what are the benefits? what would be a drawback?

- what does the small hose that leads back to the base of the carb do? Vacuum?

- should I add in a fuel check valve? If yes, benefits/drawbacks?

- anything else to consider changing? 

 

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Edited by bianchini
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The little return valve is for operability, not emissions per se.  

The vacuum hose operates the valve, nothing goes thru it.

Strip it off and there may be hot shutdown boil over in the carb with subsequent hard hot re-starting.

If you strip it off, plug the line or it may barf gasoline with a full tank of gas on a hot day.

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I can't really define what's best, but, you can plug the return line. Many people just plug one end with a bolt and some hose clamps. I pulled the entire hard line out from my car and capped it at the tank. After doing this, some experience hard re-starts when the car is warm (warm summer day). I haven't.

 

I have a 74, with 32/36 with electric choke. No return line. I removed all of the smog junk and tried to simplify the engine bay as much as possible. 

 

The base of the carb does have a vacuum port so you can just put a plug on it. It works fine.

 

Others like to keep it stock. I think it really depends on personal preference.

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9 minutes ago, thinksound_mike said:

I can't really define what's best, but, you can plug the return line. Many people just plug one end with a bolt and some hose clamps. I pulled the entire hard line out from my car and capped it at the tank. After doing this, some experience hard re-starts when the car is warm (warm summer day). I haven't.

 

I have a 74, with 32/36 with electric choke. No return line. I removed all of the smog junk and tried to simplify the engine bay as much as possible. 

 

The base of the carb does have a vacuum port so you can just put a plug on it. It works fine.

 

Others like to keep it stock. I think it really depends on personal preference.

 

Interesting stuff Mike. Thanks for the detail. mine doesnt have any stock equipment anymore and I too am trying to simplify the engine bay, which is why I am asking. 

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15 minutes ago, jimk said:

The little return valve is for operability, not emissions per se.  

The vacuum hose operates the valve, nothing goes thru it.

Strip it off and there may be hot shutdown boil over in the carb with subsequent hard hot re-starting.

If you strip it off, plug the line or it may barf gasoline with a full tank of gas on a hot day.

Jimk - when you mean strip it off, you are referring to the vacuum line AND the return line? 

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I've done 4 square lights using the steel line as the feed and deleting everything else.  Never had any probs summer starting in either 115* Sacramento or NC and FL.  All with a 32/36, just make sure the tank is vented well under the trunk somewhere.

Basically, just the single feedline going to the carb and the ventline out of the filler neck.  Everything else plugged or removed.

Edited by 2002Targa

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Mechanical pump?

 

If the return valve (the little guy that restricts the return line) is WORKING, that's a really good setup-

at idle, it reduces fuel pressure, but under throttle, it lets the carb have full volume.

 

The problems I've had with Webers flooding at idle, or wearing out their needle seats, would

be reduced or eliminated by that valve.

On the other hand, the few I've seen or had were not functioning any more.  But I buy junkers... or

used to, back when there were junkers to buy.

 

t

 

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53 minutes ago, TobyB said:

Mechanical pump?

 

If the return valve (the little guy that restricts the return line) is WORKING, that's a really good setup-

at idle, it reduces fuel pressure, but under throttle, it lets the carb have full volume.

 

The problems I've had with Webers flooding at idle, or wearing out their needle seats, would

be reduced or eliminated by that valve.

On the other hand, the few I've seen or had were not functioning any more.  But I buy junkers... or

used to, back when there were junkers to buy.

 

t

 

 

Yes, stock mechanical pump. when I pulled the return hose off the valve last night, there was gas present within the tube. As in it wasn't bone dry... you are saying if that is an indicator that the valve still works, then keep the return line in place? 

 

 

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Easy to check if the fuel return valve is functioning.  Connect a fuel pressure gauge between the valve and the Weber.

At idle (high vacuum) the valve is open allowing some gas to flow back to the tank. This reduces mechanical fuel pump (stock) pressure to about 2 psi.

With no vacuum to the valve (WOT) the valve is closed and fuel pressure to the card increases to about 3.5 psi.

Good idea to have a check valve on the return line (flowing in the direction of the tank) to prevent gas from coming back during hot weather or parking downhill.

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3 hours ago, bianchini said:

imk - when you mean strip it off, you are referring to the vacuum line AND the return line? 

Any or all, but the return line if usable, is worth something to someone installing EFI

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Great info about how the return valve works. I always like to understand the “hows” 

 

But that leads me to ask IF this return valve/path was always in the 2002 design from day 1... or was it added to later models?

 

And if added later, why was it deemed necessary at a later date. All years idled and all years ran in hot weather. What’s the reason it was added later in years if that is indeed so? 

 

Free cookies for the best answer!

 

Merci’. Randy

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It took them a while to figure it out!  :)

 

"In 1976 they had finally perfected the 2002, so they stopped making them."  c.d.

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Cold gas is better gas.  The valve keeps it circulating, that's how I always viewed it.  I kept mine functioning until I went to side drafts 5 years after buying the car (with all its smog gear still in place.) When I de-smogged, that was the only bit I kept.   

 

Later, I used the return like to feed the side drafts via an electric pump, that progressively grew into a system of overkill. 

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