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Ok guys, your thoughts on fuel systems ** UPDATE**
#1457352
06/23/13 11:55 PM
06/23/13 11:55 PM
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Joined: Oct 2003
Posts: 11,686
W. Kentucky
justinp61
OP
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OP
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W. Kentucky
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I've been chasing some carb issues and posted some questions and have got a lot of good advise  . I've also been reading other peoples posts on carb tuning and fuel systems. All this has got me thinking, dangerous I know  . Here's what I have, pump gas 408 Dart, has ran in the high 6.50s in great conditions. Bigs 950Hp, The pump is a Holley billet 12-150 150 gph pump behind a stock tank with a sump. The lines are 8an out of the tank to the pump, 8an to 1/2" aluminum to the front to a big port Holley big port regulator (6.5 psi) with a single 8an line to dual 8a carb line kit. One of the problems I'm having is at the end of a run it only has about 3 psi fuel pressure. Looking at my LM-2 logs it's getting more lean as the run progresses, not popping lean just steadily leaning out. Also I noticed no real differences in the mph when making jet changes. Is my problem the 8an from the tank to the pump? the pump only has 3/8 npt inlet and outlet. Is it the pump? Or something else? Thanks, Justin
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Re: Ok guys, your thoughts on fuel systems
[Re: justinp61]
#1457353
06/24/13 12:17 AM
06/24/13 12:17 AM
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Joined: Dec 2005
Posts: 11,721
Fulton County, PA
CMcAllister
Mr. Helpful
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Mr. Helpful
Joined: Dec 2005
Posts: 11,721
Fulton County, PA
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The -8 stuff from the pump to the carb is probably sufficient IF you can keep it full and pressurized. I would want at least a -10 from the tank to the pump. -12 is even better. If there is only one outlet on the tank, it needs to be at least 1/2 NPT. 2 3/8NPT bungs could be used with 2 lines to a 3/8x3/8x1/2 tee, then a -10 to the pump. Best choice would be a hole in the tank with a -10 or -12 AN tank fitting. The pump needs to be stepped up. Lots of opinions on which to use but there is no such thing as too big. Main line volume and pressure need to be increased. Make certain the aluminum line to hose connections are done correctly.
If the results don't match the theory, change the theory.
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Re: Ok guys, your thoughts on fuel systems
[Re: justinp61]
#1457356
06/24/13 02:15 AM
06/24/13 02:15 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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What the others are saying about the larger size from the tank to the pump is true.. remember pumps dont really suck fuel in... the pump creates the negative pressure so atmospheric pressure pushes the fuel in (just like the cyl is doing for the air/fuel in the engine)... now do you have a filter before the pump and what size micron is it.. you dont want a fine filter there(just a tree stopper) and the filter should be able to flow what the pump does(most people run way to small of filters flow wise).... have you done a flow check on your pump... next thing would be to make sure it has the proper voltage... also if you run 2 lines into the pump use a Y fitting and not a T EDIT Make sure you have a good vent thats not partly plugged on the tank 
Last edited by MR_P_BODY; 06/24/13 02:19 AM.
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Re: Ok guys, your thoughts on fuel systems
[Re: Cab_Burge]
#1457358
06/24/13 08:49 AM
06/24/13 08:49 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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Quote:
What size nedles and seats in your carb? If there .110 or smaller try a set of Holley .120 Vitons on pump gas 
I agree on the needle/seats BUT he is dropping pressure
which is read before that point... so in my opinion
its a flow/volume issue(at this time but could change
to a needle/seat issue later once he gets the flow)
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Re: Ok guys, your thoughts on fuel systems
[Re: MR_P_BODY]
#1457359
06/24/13 10:23 AM
06/24/13 10:23 AM
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Joined: Oct 2003
Posts: 11,686
W. Kentucky
justinp61
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OP
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Thanks guys. The needles and seats are .110, but they shouldn't affect the pressure drop in the line. I understand they could affect flow to the carb. There is no filter before the pump, went through that a few years ago  . I upgraded the vent to 3/8" when I installed the 1/2" line and bigger pump. I'll check to make sure nothing has got in it. This is the carb fuel line http://www.summitracing.com/parts/rus-641153/overview/.I can install a 10an line but I don't know if I can get a 3/8" npt to a 12an fitting.
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Re: Ok guys, your thoughts on fuel systems
[Re: justinp61]
#1457360
06/24/13 11:30 AM
06/24/13 11:30 AM
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Joined: Oct 2003
Posts: 7,506
Az
Crizila
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master
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Posts: 7,506
Az
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Is this a dead head system? Here is what I did to solve my -8 sump problem. Magnafuel sells the "Y" fitting. Make sure the tubing has no kinks or other restrictions. What is the post filter micron? Avoid any right angle fittings if you can.
Fastest 300
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Re: Ok guys, your thoughts on fuel systems
[Re: justinp61]
#1457364
06/24/13 12:34 PM
06/24/13 12:34 PM
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Joined: Jul 2004
Posts: 19,318
State of confusion
Thumperdart
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State of confusion
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Have you done the 1-gallon fuel flow test yet?
72 Dart 470 n/a BB stroker street car `THUMPER`...Check me out on FB Dominic Thumper for videos and lots of carb pics......760-900-3895.....
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Re: Ok guys, your thoughts on fuel systems
[Re: justinp61]
#1457365
06/24/13 12:44 PM
06/24/13 12:44 PM
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Joined: Apr 2005
Posts: 12,271
Overpriced Housing Central
RobX4406
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Quote:
Yes it's a dead head system. The filter is a Aeromotive 40 micron, I removed the filter element and it still only had 3 psi crossing the line. I'll do a flow test this afternoon and see what I have.
I never run anything smaller than a 100 micron for a pre filter. IMO 40 is too fine and may cause the pump to cavitate.
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Re: Ok guys, your thoughts on fuel systems
[Re: RobX4406]
#1457366
06/24/13 01:25 PM
06/24/13 01:25 PM
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Joined: Oct 2003
Posts: 11,686
W. Kentucky
justinp61
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OP
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Quote:
Quote:
Yes it's a dead head system. The filter is a Aeromotive 40 micron, I removed the filter element and it still only had 3 psi crossing the line. I'll do a flow test this afternoon and see what I have.
I never run anything smaller than a 100 micron for a pre filter. IMO 40 is too fine and may cause the pump to cavitate.
The filter is at the carb, there is no pre pump filter.
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Re: Ok guys, your thoughts on fuel systems
[Re: Thumperdart]
#1457369
06/24/13 02:17 PM
06/24/13 02:17 PM
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Joined: Oct 2003
Posts: 11,686
W. Kentucky
justinp61
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OP
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W. Kentucky
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Quote:
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Yes it's a dead head system. The filter is a Aeromotive 40 micron, I removed the filter element and it still only had 3 psi crossing the line. I'll do a flow test this afternoon and see what I have.
I never run anything smaller than a 100 micron for a pre filter. IMO 40 is too fine and may cause the pump to cavitate.
The filter is at the carb, there is no pre pump filter.
Again, did you flow the pump? 
Will do this afternoon when I have some help.
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Re: Ok guys, your thoughts on fuel systems
[Re: justinp61]
#1457370
06/24/13 03:15 PM
06/24/13 03:15 PM
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Joined: Aug 2003
Posts: 43,307
Bend,OR USA
Cab_Burge
I Win
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I Win
Joined: Aug 2003
Posts: 43,307
Bend,OR USA
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Quote:
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Yes it's a dead head system. The filter is a Aeromotive 40 micron, I removed the filter element and it still only had 3 psi crossing the line. I'll do a flow test this afternoon and see what I have.
I never run anything smaller than a 100 micron for a pre filter. IMO 40 is too fine and may cause the pump to cavitate.
The filter is at the carb, there is no pre pump filter.
Again, did you flow the pump?
Will do this afternoon when I have some help.
If you can flow it through the float bowls first do that and then through the hoses only I had a fuel delivery problem years ago and found out that some pumps will pump more volume through a restriction than they will without the restriction  the restriction can make some of the larger pumps work harder which ends up increasing the volume through the system with the restrictions  Test, test and tests some more
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
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