Running out of fuel street HEMI
#2136081
08/18/16 07:02 PM
08/18/16 07:02 PM
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Joined: Jul 2007
Posts: 36 MN
36viper
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OP
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Hi guys! I have always had an apparent fuel delivery problem in my '68 HEMI Charger. On hard acceleration from slow roll or stop, it begins to pop and loose power around 80mph.. It pulls really hard if one is just cruising around in 4th gear and steps on the throttle. Its also really strong up to 80 mph when accelerating hard. After experiencing the problem, I installed a high output fuel pump, but it still didn't cure the issue. The 426 HEMI has a moderate build and requires 50% race gas. Someone told me that I should put a fuel flow restrictor in the return line to the tank, that is designed to prevent vapor lock, that the carbs would get more fuel and wouldn't run low on sustained acceleration. He said I should drill a certain sized hole into a bolt, and insert in into the 3/8" line to reduce the amount of gas that's returning to the tank. I'm thinking of putting a vice grip on the return line, to see if it solves the problem, then I'll make a restrictor for the return line if the vice grip solves the problem. The fuel gauge just quit working, so I'll check the filter on the end of the pick-up line when I'm working on the sending unit. Maybe it's plugged, or maybe there is an air leak in the fuel line somewhere???
Thank you Moparts for the help!
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Re: Running out of fuel street HEMI
[Re: 36viper]
#2136088
08/18/16 07:12 PM
08/18/16 07:12 PM
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Joined: Jun 2003
Posts: 52,972 Romeo MI
MR_P_BODY
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Master
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Romeo MI
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Is it a mech pump or electric... what carbs.. what size needle/seat.. have you done a flow check(gals per minute).. do you still have the stock sock on the pick up... do the filters have enough flow... thats a start
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Re: Running out of fuel street HEMI
[Re: 469runner]
#2136308
08/19/16 12:01 AM
08/19/16 12:01 AM
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Joined: Jul 2007
Posts: 36 MN
36viper
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It's a new high output mechanical fuel pump. It didn't seem to help with the supply problem. I'll check the sock this week.
Thank you Moparts for the help!
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Re: Running out of fuel street HEMI
[Re: MR_P_BODY]
#2136310
08/19/16 12:04 AM
08/19/16 12:04 AM
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Joined: Jul 2007
Posts: 36 MN
36viper
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OP
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Factory carbs and jetting, new mechanical pump.
Thank you Moparts for the help!
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Re: Running out of fuel street HEMI
[Re: 36viper]
#2136314
08/19/16 12:10 AM
08/19/16 12:10 AM
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Joined: Sep 2015
Posts: 1,096 Australia
ozymaxwedge
super stock
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super stock
Joined: Sep 2015
Posts: 1,096
Australia
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From reg to carb you want 6-7 psi running, having a gauge set up so you can see it when the problems start will tell you. Is your fuel pressure dropping off ?
Last edited by ozymaxwedge; 08/19/16 12:12 AM.
1963 Plymouth Max Wedge 1971 Barracuda
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Re: Running out of fuel street HEMI
[Re: 36viper]
#2136323
08/19/16 12:23 AM
08/19/16 12:23 AM
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Joined: Jan 2003
Posts: 4,329 Morrow, OH
markz528
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master
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Posts: 4,329
Morrow, OH
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I struggled with a high output mechanical pump on my 440. I consider myself pretty competent and I gave up. Went electric.
Did a bunch of testing and tried a couple of pumps. All were Carter.
67 Coronet 500 9.610 @ 139.20 mph 67 Coronet 500 (street car) 14.82 @ 94 mph 69 GTX (clone) - build in progress......
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Re: Running out of fuel street HEMI
[Re: ozymaxwedge]
#2136344
08/19/16 12:45 AM
08/19/16 12:45 AM
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Joined: Aug 2003
Posts: 43,719 Bend,OR USA
Cab_Burge
I Win
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I Win
Joined: Aug 2003
Posts: 43,719
Bend,OR USA
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From reg to carb you want 6-7 psi running, having a gauge set up so you can see it when the problems start will tell you. Is your fuel pressure dropping off ?
To fix the problems you need to know first what they are I use to race two non original street Hemi cars in NHRA stock back in the early to mid 1970s. Both had 5/16 lines and pickups, both needed the Carter 3 valve race Hemi H.P. NASCAR type pumps to run with enough fuel supply Good luck, let us know what you find and do to fix that problem
Last edited by Cab_Burge; 08/19/16 12:47 AM.
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
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Re: Running out of fuel street HEMI
[Re: 36viper]
#2136481
08/19/16 10:17 AM
08/19/16 10:17 AM
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Joined: Jan 2003
Posts: 13,492 Marion, South Carolina [><]
an8sec70cuda
I Live Here
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I Live Here
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Posts: 13,492
Marion, South Carolina [><]
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Get rid of the sock filter in the tank.
Remove and measure the length of the fuel pump pushrod to make sure it isn't worn.
You should be able to eliminate the return line.
CHIP '70 hemicuda, 575" Hemi, 727, Dana 60 '69 road runner, 440-6, 4 speed, Dana 60 '71 Demon 340, no drivetrain, on blocks behind the barn '73 Chrysler New Yorker, 440, 727, 8.75 '90 Chevy 454SS Silverado, 476" BBC, TH400, 14 bolt '06 GMC 2500HD LBZ Duramax
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Re: Running out of fuel street HEMI
[Re: Thumperdart]
#2136746
08/19/16 06:07 PM
08/19/16 06:07 PM
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Joined: Nov 2003
Posts: 36,041 Lincoln Nebraska
RapidRobert
Circle Track
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Circle Track
Joined: Nov 2003
Posts: 36,041
Lincoln Nebraska
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X3, see what you have AT the carbs at the offending RPM/load with an accurate gauge on the cowl or plumbed inside (just for the test of course! or with an isolator for safety)
live every 24 hour block of time like it's your last day on earth
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Re: Running out of fuel street HEMI
[Re: cudaman1969]
#2136915
08/19/16 10:48 PM
08/19/16 10:48 PM
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Joined: Jun 2003
Posts: 52,972 Romeo MI
MR_P_BODY
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Master
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Romeo MI
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Wasn't the special OEM fuel filter used on the original cars suppose to be a vapor seperator? Not for liquid returns is what I remember I never heard of a return line to the tank, vapor can like Cab said, could be broke and just circling back to pump. Hemi cars came with 3/8 line. That stock pump "should" pump enough fuel for the carbs, cover the lines from heat to stop vapor lock. My two cents. The sock in the tank will separate water until its totally under water.. but its not 100%.. the return just has a orifice.. pretty sure back then it was .060 EDIT Yes they did have a return to the tank... any of the so called performance engines had a return.. any that had a 3/8 supply had a return
Last edited by MR_P_BODY; 08/19/16 10:54 PM.
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Re: Running out of fuel street HEMI
[Re: MR_P_BODY]
#2136986
08/20/16 12:37 AM
08/20/16 12:37 AM
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Joined: Jan 2004
Posts: 8,637 fredericksburg,va
cudaman1969
master
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master
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Posts: 8,637
fredericksburg,va
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U Wasn't the special OEM fuel filter used on the original cars suppose to be a vapor seperator? Not for liquid returns is what I remember I never heard of a return line to the tank, vapor can like Cab said, could be broke and just circling back to pump. Hemi cars came with 3/8 line. That stock pump "should" pump enough fuel for the carbs, cover the lines from heat to stop vapor lock. My two cents. The sock in the tank will separate water until its totally under water.. but its not 100%.. the return just has a orifice.. pretty sure back then it was .060 EDIT Yes they did have a return to the tank... any of the so called performance engines had a return.. any that had a 3/8 supply had a return Return line or vent line? How big a performance engine did it have to be? My a-body m-code 440 only has one 3/8 line, maybe because it started as a 383?
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Re: Running out of fuel street HEMI
[Re: cudaman1969]
#2137037
08/20/16 01:31 AM
08/20/16 01:31 AM
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Joined: Jun 2003
Posts: 52,972 Romeo MI
MR_P_BODY
Master
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Master
Joined: Jun 2003
Posts: 52,972
Romeo MI
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U Wasn't the special OEM fuel filter used on the original cars suppose to be a vapor seperator? Not for liquid returns is what I remember I never heard of a return line to the tank, vapor can like Cab said, could be broke and just circling back to pump. Hemi cars came with 3/8 line. That stock pump "should" pump enough fuel for the carbs, cover the lines from heat to stop vapor lock. My two cents. The sock in the tank will separate water until its totally under water.. but its not 100%.. the return just has a orifice.. pretty sure back then it was .060 EDIT Yes they did have a return to the tank... any of the so called performance engines had a return.. any that had a 3/8 supply had a return Return line or vent line? How big a performance engine did it have to be? My a-body m-code 440 only has one 3/8 line, maybe because it started as a 383? If t was factory and labeled HP it had 3/8 supply and a 1/4 return and a 1/4 vent... a 3 tube bundle clamped together in the 70s with the charcoal canister up front.. otherwise it had the vent in the frame rail on older years but still had the 3/8 and 1/4 going forward if it went into the fame rail it was likely a 3/16 vent
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