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HuD 91gt

Hard line between mech fuel pump and SU

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Hello,

I spent a good thirty minutes searching the catalogs at jegs and summit trying to figure out a way to run a straight hard line (my stock fuel "rail" isn't all that pretty right now) from the mechanical pump to the SU's.

Two ways to go about this,

A) find an original mech fuel pump and take out the "flared" outlets and swap them with a brake fitting or AN. The same would have to be done with the SU's. Possible?

B) the aftermarket pumps available these days are not rebuildable, thiey only have the "flared" outlet to accept a rubber line. Is there some sort of adaptor on the market to attach to this to run to a hard line? This is all clearly cosmetic so I don't want it to be too big of a hassle but someone must have come across this in the past.

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I haven't seen the fitting you're looking for but another hose barb, the desired size could be attached to the f. pump using a short piece of flexible fuel line. I imagine it wouldn't have to be 1 1/2"-2" long & use two hose clamps.

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Yeah, that seems to be all I can think of as well. No real way tk completely get rod of the rubber lines. Banjo bolts for the SU's don't seem to be an issue though.

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The outlet hose barb on my rebuilt OEM mechanical fuel pump turned out to be BSPT/BSPP, 1/8" thread. 1/8" NPT would not thread in at all. Got the BSPT to NPT adapter from McMaster-Carr, also an NPT Tee for the hose barb to the fuel line and my AN (with NPT adapters) hose to the F.P. gauge. A little complicated but it works.

 

SU fittings are metric. Should be standard metric banjo bolts available with threaded (maybe AN) inlets. Seen them on a few Z cars.

 

I can imagine a setup that would make it difficult to remove the float bowl lids. I had to remove and replace the lids many times to adjust the floats the way I like.

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You make a very good point about the removal of the float lids. I didn't even think of that. What brand is your fuel pump?

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It's a Kyosan, got it (rebuilt) at Autozone a few years ago. Now they only have the stamped metal ones. Seems like there must be some around on the shelves of some warehouses. I ordered one from Napa that they said was OEM type, picture in their catalog was old style, but it wasn't.  The part numbers are the same so can't tell from that. Called Rock Auto to ask about it, they said they had old style as shown in their online catalog, but couldn't open the box and look before sending it, so I declined. Couple days later the picture was gone from their catalog, guess they were heads-up enough to go check and revise it.

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Well, after input from the forum, I think datsun designs the rubber lines for a reason. Easy removal, vibrations etc.

I have cancelled that idea, but have purchased all the parts to make a new stock su fuel line. The one thing I did not take into consideration is the smaller return line. Is this thinner diameter return line, causing the path of least resistance to be to the carbs, thus filling the fuel bowls? If I run the same diameter line back to the frame rail (where it will then get smaller), will my carbs be getting fuel or will the fuel automatically take the return back to the tank because it offers little resistance?

Anyone understand how the return works?

Edited by HuD 91gt

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I should clarify, I purchased 5/16" fuel line and was going to use this for the entire "rail", back to the stock hard lines (which run back to the tank), where they would then differ in size.

Or is there some sort of spring loaded valve which makes the fuel run to the carbs and blocks the return line until the float valves close?

Edited by HuD 91gt

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The very end of the return line has a smaller hole in it which will reduce flow and increase pressure to the required amount ay the carbs.  Look at the end of the stock line and you will see the smaller hole.  It has been said many times not to make any changes to that end, ie: reaming it out to increase flow which will reduce back pressure to the carbs.  Hope this helps.

 

Bonzi Lon

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Thanks Bonzi.  I wish I had known this earlier. Oops.  I have a feeling i'm opening a can of (hard tuning) worms with this little project.  Maybe i'll experiment anyhow since I have all the parts. I purchased 5/16" line, but it sure looks a lot larger then whats on the car now.   Z forums may have led me astray.  Although, with the little hole controlling the flow, the fuel line size shouldn't matter?  

Bruce, thanks for letting me know. I probably should just purchase one, but it's more fun to make your own.

Edited by HuD 91gt

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The fuel line from the tank can be oversized. It won't hurt a thing. 

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