Farmer Posted January 22, 2011 Report Share Posted January 22, 2011 Should I run a fuel return line while running a weber carb? Larry Quote Link to comment
izzo Posted January 22, 2011 Report Share Posted January 22, 2011 Nah, dont need it. Remember, weber only needs about 3 to 3.5lbs of pressure. Quote Link to comment
datsunaholic Posted January 22, 2011 Report Share Posted January 22, 2011 They run a hell of a lot better with one. The low pressure requirement makes it more important. Since your truck already HAS one, just leave it hooked up. This is even more true when using an electric fuel pump- stock or aftermarket. I've had a couple trucks where prior owners removed the original fuel rail to "clean it up", putting a hose from the pump to the carb (which looks worse than just keeping the stock lines) and capping off the return (well, one did. The other left it wide open). Both trucks had serious flooding issues- the fuel pressure at even idle far exceeded the spring pressure on the float valve, and fuel poured in the carb throat. The one with electric flooded just turning on the key. I acquired a stock fuel rail from the junkyard (which has a built-in return system that consists solely of an orificed return) and the flooding problems were no more. To add to it, using the return keeps fuel flowing constantly, keeping it filtered, and it lets the pump run freely without getting backpressure which can make them heat up or wear out faster. And it means no need for add-on fuel pressure regulators. Quote Link to comment
izzo Posted January 22, 2011 Report Share Posted January 22, 2011 Good info, never ran a return line and never had those issues. If i ever do, i know why :D My wagon had an electric pump on it. It T'd and went to the carb, and to the return line. It ran two filters, seemed to work great. Quote Link to comment
Farmer Posted January 22, 2011 Author Report Share Posted January 22, 2011 I took my oem fuel rail off long time ago, but of course never ran engine until now. Had the Dual su's on but went with a single weber for break in period. I guess I have to figure out something. Thanks, Larry Quote Link to comment
HRH Posted January 22, 2011 Report Share Posted January 22, 2011 A Weber 32/36 isn't that critical for backflow, but if you run a 38/38 or bigger, you'll definitely need a return line. They're a bit more fussy. Also, running an electric pump will also necessitate a return even if they're close to original pressure. Best carb application is still the Nikki diaphragm style mechanical pumps. They're hard to find though. Quote Link to comment
VintageRice Posted January 25, 2011 Report Share Posted January 25, 2011 I just rebuilt a Weber 32/36 and am installing it on my L18 for the first time. It came off a L20b and had a inlet but the other side was just plugged with a brass fitting. I was wondering if it needed a return line, and it made sense to me that it WOULD need one since a 510 came factory with it. Anywhoo, I plan on running a return. Seems like the fuel pump would just be building up pressure if it was blocked. That pressure has to relieve somwhere..... One question. Does it matter which side you use for a inlet and/or a return? Or are they switchable per your application? Quote Link to comment
banzai510(hainz) Posted January 25, 2011 Report Share Posted January 25, 2011 Im running a 38/38 on my 521 now and seems fine. I wouldnt worry about it. Quote Link to comment
VintageRice Posted January 26, 2011 Report Share Posted January 26, 2011 Went to napa tried to find the fitting for my return line. They didnt have anything with those threads. Said the heck with it, went home, connected a few lines and tried to fire it off. It ran great for a few seconds then totally flooded. Aparently I'm not a very good ca rebuilder. It was dripping fuel into the intake below the butterflies. I'm going to do a search and then maybe start a new thread on this. I don't want to hyjack this thread to bad ;) Quote Link to comment
izzo Posted January 26, 2011 Report Share Posted January 26, 2011 Strange, ive never ran a return line except when using an electric pump, never had it flood like that. i can run my L16 for very long periods of time in my driveway and it doesn't effect it at all. Same with my l20, and other cars... Quote Link to comment
VintageRice Posted January 26, 2011 Report Share Posted January 26, 2011 Well, I talked with my personal mechanic tonight. He said holleys and edelbrocks work fine on v8's that have fuel pumps putting out way more pressure than 3.5lbs and the needle and seat hold back the pressure all day long on those. Sooo now I'm convinced that no return line is fine and I just need to re-adjust my floats. Will post the results. :D Quote Link to comment
Charlie69 Posted January 26, 2011 Report Share Posted January 26, 2011 Presuure regulator at 3.5 lbs pressure and you are fine on a Weber 32/36 Quote Link to comment
VintageRice Posted January 27, 2011 Report Share Posted January 27, 2011 How much pressure does a l20b fuel pump put out? Quote Link to comment
Z-train Posted January 27, 2011 Report Share Posted January 27, 2011 If return lines aren't needed,then why did those"idiot factory engineers"design one for 78 & later trucks?You don't need a pressure reg-just make sure the return"orifice" is properly sized and is restriction free. VR-i'm getting 3.5 to 4 with the above mentioned return line with w factory mechanical pump. And yes,you can use either side for a feed.I have my FP guage in the un-used side. Quote Link to comment
Sealik Posted February 1, 2011 Report Share Posted February 1, 2011 (edited) Should I run a fuel return line while running a weber carb? Larry Yes.....use the return line,.... and set the reg at 2.5lb Try 3lb if you like....and see if there's an improvement. Probably not. That's if you got a reg of course... :) Edited February 1, 2011 by Sealik Quote Link to comment
Farmer Posted February 13, 2011 Author Report Share Posted February 13, 2011 Seems to be working fine with out return. Thanks for all the inputs Larry Quote Link to comment
datzenmike Posted February 13, 2011 Report Share Posted February 13, 2011 The L20B motors tend to run hot. The under hood temps soar and will heat soak the carb and fuel rail causing the gas to boil causing vapor lock and hard re-starts. To prevent this Nissan installed a return line to allow cooler fuel to be constantly circulated past the carb. The return line has a pin hole restriction so the pump can push against it and build some pressure. Without the small orifice fuel would just by pass the carb and return to the tank. The L series pumps are self regulated to put out 3-3.9 PSI so if you feel that a Weber can only handle 3 or less then a regulator is in order. Another advantage of this is, that the contents of the fuel tank are constantly circulated through the fuel filter to collect any solids that would normally form or collect in the tank. Return orifice Quote Link to comment
VintageRice Posted February 13, 2011 Report Share Posted February 13, 2011 Datzen mike. Your Sr. are a supergenius ! Quote Link to comment
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