View Full Version : fuel system
05-04-2010, 06:38 AM
just wondering what most of you guys run for a fuel system with a blower.ive been tinkering with pumps and currently i have a walbro 255 feeding another 255 inline and a aeromotive regulator and cant get this thing under control.im running a demon carb 650 73 jets up front and no secondary jets at all and still lean.i run a vortech v1 and a 2.95 pulley on my mild sbc and it shouldnt need more than 500hp at the crank at 7psi of fuel to the carb.im getting really frustrated but want to keep away from using pumps like a1000 that recquire controllers to keep from burning out as i want this to be a street car.ive seen people running three bosch 441 and three walbros so maybe thats the route ill go.maybe a sump on the stock tank.one intank pump and two feeding off the sump.idk anymore
05-04-2010, 03:22 PM
you want a serious and honest answer?
get a better carb!
I need more info on the carb (part number, etc), the fuel delivery side is more than enough (you are running a fuel return line from the regulator right?). Is this a vacuum secondary or mechanical secondary carb (i'm guessing vacuum secondary here saying you said there is no metering block in the rear only a metering plate, and that's not a good choice for forced induction at all).
05-04-2010, 09:10 PM
i use to run a holley 750 hp and it was great except it wasnt pressure sealed for blow through so gas leaked out,only had squirters upfront,no 4 corner idle, and no boost reffrenced powervalve/
i later acquired a demon 650 sealed carb specifically for blow through,mech secondary,boost reffrenced power valve,4 corner idle,and had front and rear squirters.i chose the smaller size because its on a heavy suburban and the forced air would overcome the extra 100cfm anyway.plus ive read the demon 650 flows nearly asmuch as a holley 750.
this fuel problem is starting to get old.im going to run two walbro 255s intank feeding another 255inline as a pusher pump all -6 feed lines and -8 return all the way back and seeing where that leaves me.
05-04-2010, 09:41 PM
why the hell are you adding a 100 fuel pumps to this thing? Adding another fuel pump is not going to do **** for you right now. You have enough fuel pump already to support 500+hp to the wheels, which i doubt you're even close.
Instead of guessing, and jumping into spending money, why dont you tell me alittle about your setup?
I'm taking its blow through not draw through, any carb can be pressure sealed, if you were pissing gas out of the carbs something is wrong. take a pic of the supercharger setup (i'm taking this is something like a pro-charger or vortec charger?) What is your fuel pressure out of boost, what is your fuel pressure in boost? What kind of fuel regulator do you have, and do you have a return running to the tank? A demon mechanical secondary carb should have a metering block in the back not a metering plate, meaning you have jets back there. What make of demon is it other than '650' because they make about 50 different kinds of Demon 650 carbs.
How can I help you if you wont help me by giving out detailed information?
05-05-2010, 06:24 AM
the intank pump is a couple of years old so im just going to tackle this thing once so i can narrow that out.at idle im able to put afr's where ever i want them but soon as boost starts to climb i go from 11 slowly back to the 14 range and it stays there.while 14 is an ideal range for a clean idle id like to be in the 11's under boost to be on the safe side.for some reason fuel isnt keeping up with carb when boost comes in.
i run a demon 650 blow through the carb is called just like that and it does have jets outback but i removed them completely to help get more fuel to this thing.i bought a jetbox and tried rejetting but even removing the secondary jets completely improved afr's only to a couple more rpm so that is why i feel as i dont have enough pump.no secondary jets introduced a bit more fuel and helped but after a certain rpm the afr just goes coasting like it cant keep up.
the blower is a vortech v1 centrifugal blower i run a 2.95 pulley its air to air intercooler and i run a carb hat over the carb not a pressure sealed box.the truck had a walbro 255 intank 13301 aeromotive bypass regulator and all stock feed and return lines.i then adding an inline 255 and instead of making it better it made it a bit leaner.if the intank pump is the same as the inline and im using the inline as a pusher pump afr should have improved under boost instead it decreased slightly.that is why i am thinking its time for a new pump setup.
05-05-2010, 10:23 AM
Do you have a fuel pressure gauge........... since your running a carb you dont need the pressure us EFI guys do. 1 good 255 will be pleanty for your application. I think you may have a float issue also do you have a true WB installed
05-05-2010, 10:48 AM
a single walbro 255 maxes out at about 600whp on a lt1 f-body. you have more pump than you'll ever need already.
05-05-2010, 01:02 PM
I went with a mech. pump to get away from the electric pumps. Lots of people run the 255 and have nothing but good things to say about it, so i dont think pumps are your problem. If you are running stock fuel lines, could you have enough pressure, but not enough volume? Stock fuel lines are not very big, also where is your regulator mounted, before the carb or after a fuel log? These guys got me pointed in the right direction when i was having the same issue, there are lots of people on here that can help. Here is a link that has a diaghram of how i set mine up. 3A is the best way.
05-05-2010, 05:34 PM
i do have a gauge right on the fuel log and i run a aem wideband.
tanks already down so im already working on changing the lines out and the regulator is a aeromotive mounted in the engine bay right before the carb.
im starting to see why few people go blow through carb.its a whole nother headache but it seems everythings hard the first time around.hopefully ill figure this thing out.
05-09-2010, 02:44 PM
So did the fuel pump make a difference?
You need a fuel pressure gauge that you can read while driving for starters. Blow through carb is pretty damn easy to do, you just have to have the knowledge on how a carb works and what different things will do to it. Most people think tuning a carb is done simply by changing jets. little do they know there is much more details than that.
As Fast95 learn't, you have to feed the carb with fuel first through a log, then to a regulator, then return. feeding the reg then the carb is not the proper way to do it, and its a guaranteed way to starve the engine of fuel. You should have a base pressure of no more than 8psi (i recommend 7psi). now with a fuel pressure gauge using a boost referenced fuel pressure reg, you should see an increase of fuel pressure 1psi for every 1psi of boost. so at 10psi of boost you should have 17psi of fuel pressure. The fuel pressure should never ever drop off during a run, if it does its a good indication of ether a regulator issue, pump issue, or line issue. The Regulator should be referenced from the carb hat, and not the intake manifold.
For the love of god, do not be a retard, install some damn jets in the rear metering block. I would start off with #75 jets in the primaries, and #85 jets in the secondaries and tune from there. If you still find you are lean, then you can try jetting up and see if that makes a difference, if not you have to figure out why. this is where the fuel pressure gauge comes in handy, if the pressure stays solid then I would start by seeing what size needle and seat is in the carb. it should be a minimum of .120 for a forced induction application, .130 is recommended and when you get into BIG power (800+) then a .150 is needed. If that still doesnt make a difference, you should be verifying the primary power valve is opening, this can be done by plugging it and noting any differences in AFR. The BT Demons come with a powervalve reference port on the throttle plate on the primary side in the center i believe, you may need to reference that. If the power valve is opening, and fuel delivery is good but AFR is still not the greatest. Then there are a few other tricks we can try other than jetting the hell out of it. you should be able to get great fuel economy out of boost, and still supply enough fuel under boost that it wont starve the engine.
One thing i would HIGHLY recommend doing, is vent tube extensions. Buy about 2ft of rubber/plastic fuel line 5/16" in size, cut two pieces 8" in length, you want to slide them onto the carb's vent tubes, and run them in the hat (zip tie them together) and point them in the direction of air flow coming in to the hat and see how that is.
do abit of leg work then come back on here and give me a few detailed updates of what did what, etc. if we need to then we can start tuning via other methods or even try a few more things.
Powered by vBulletin® Version 4.2.0 Copyright © 2013 vBulletin Solutions, Inc. All rights reserved.
SEO by vBSEO