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fuel pressure

Printed From: TheAMCForum.com
Category: The Garage
Forum Name: AMC V8 Engine Repair and Modifications
Forum Description: AMC-made V8 engine mechanical, ignition and fuel from basic repair to high-perf modifications
URL: https://theamcforum.com/forum/forum_posts.asp?TID=98530
Printed Date: Mar/29/2024 at 6:20am
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Topic: fuel pressure
Posted By: 401fanatic
Subject: fuel pressure
Date Posted: Feb/11/2019 at 12:26pm
Fresh 401 modified and about 5 hrs on it now. When it sits for a while I loose fuel pressure prime. It cranks a very long time before I see fuel in my sight glass at the carbs.  New carter street strip mechanical pump. Once I get fuel to the carbs it runs great. Why am I loosing prime all the way back to the tank?

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74 javelin 401 t-10 3.91 twin grip.
74 javelin 401 998 3.54 twin grip.                            



Replies:
Posted By: Trader
Date Posted: Feb/11/2019 at 12:36pm
It's more likely your fuel is evaporating in the carburetor, and without knowing your pump, fuel vapor pressure is building in the fuel line to the carburetor and possibly the line under the car (depending on exhaust pipe run), pushing fuel back to the tank.
Your tell on this is the empty sight glass.
Start it up from cold and run for 2 minutes and shut down, hood open. If the sight glass still has fuel, it's a temperature problem. If the sight glass goes empty then you have a fuel pump problem.


Posted By: 401fanatic
Date Posted: Feb/11/2019 at 12:55pm
It would be a temp problem then. I’ll lol into it a little closer. Thx.

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74 javelin 401 t-10 3.91 twin grip.
74 javelin 401 998 3.54 twin grip.                            


Posted By: PHAT69AMX
Date Posted: Feb/11/2019 at 1:21pm
Today's Gasoline?... Pass Side Exh Heat Riser in place?... Blocked off Intake Heat Crossover?
Modern aftermarket import offshore Fuel Pump?... Fuel Pressure Gauge?...  Regulator?...
What Carburetor?...  Cast Iron Intake?...  1" Phenolic Carb Spacer?...


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Link to a http://www.youtube.com/watch?v=MySiKQsmWxU" rel="nofollow - Short YouTube Burnout Video



Posted By: 401fanatic
Date Posted: Feb/11/2019 at 1:40pm
new carter street strip mechanical pump. New carter 500 cfm carbs calibrated for duel quad applications. 93 octane pump gas. Headers. Cross over blocked. Offy aluminum duel quad intake. No Spacers. Generic fuel pressure guage. 

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74 javelin 401 t-10 3.91 twin grip.
74 javelin 401 998 3.54 twin grip.                            


Posted By: 401fanatic
Date Posted: Feb/11/2019 at 1:41pm
no regulator. 6 psi. 

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74 javelin 401 t-10 3.91 twin grip.
74 javelin 401 998 3.54 twin grip.                            


Posted By: 401fanatic
Date Posted: Feb/11/2019 at 1:48pm
Edelbrock carbs. My bad. 

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74 javelin 401 t-10 3.91 twin grip.
74 javelin 401 998 3.54 twin grip.                            


Posted By: Trader
Date Posted: Feb/11/2019 at 2:02pm
Running hose and not metal lines can be more beneficial to fuel evaporation. Not as pretty.
Re-routing the fuel lines to the fender wells, or with two carbs, run tight against the carburetors and then away from the heads at the front of the engine.  Run the lines on a down slope. Shield from exhaust pipes and hot surfaces. 


Posted By: PHAT69AMX
Date Posted: Feb/11/2019 at 2:05pm
Agree with Trader, need to do something to determine if Heat or Pump related.
Confidence with modern aftermarket parts is dubious, and modern fuel formulation.
Does Indiana go with different "Winter Formula" fuel ?


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Link to a http://www.youtube.com/watch?v=MySiKQsmWxU" rel="nofollow - Short YouTube Burnout Video



Posted By: 401fanatic
Date Posted: Feb/11/2019 at 2:19pm
I’m shooting from the hip and assuming it is heat related. Pump seems fine and at least 6 psi. Winter formula in southern Indiana is something I’ll have to check into. I don’t know.  Worst case I could go with a electric pump and prime before starting but I’ve never really cared for electric pump wine noise.

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74 javelin 401 t-10 3.91 twin grip.
74 javelin 401 998 3.54 twin grip.                            


Posted By: wheelz
Date Posted: Feb/11/2019 at 3:02pm
I run the dual quad Edelbrock AVS 500 carbs on a ram and have no issues. I/2 hard line to a fuel cell in the trunk and use the Robb MC mechanical pump with Startlite hose to the carbs. You may have a volume problem with the carter not keeping up or the floats could be off. When I received my carbs I remember checking the floats and one was way off. If not are you running steel lines? May need an insulating spacer(s) to keep fuel from cooking off


Posted By: 401fanatic
Date Posted: Feb/11/2019 at 3:26pm
ya. I’m gunna have to dig a little deeper. Thanks to all who responded. 

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74 javelin 401 t-10 3.91 twin grip.
74 javelin 401 998 3.54 twin grip.                            


Posted By: Rebel Machine
Date Posted: Feb/11/2019 at 8:13pm
I'd bet you're boiling the fuel in the carbs after shutting it off. My Machine did this. After shutting it off it would be around five minutes and I'd see fuel dripping out of the carb's boosters going down the venturi.

Is there fuel in your oil?

-Steve-



Posted By: 401fanatic
Date Posted: Feb/12/2019 at 6:46pm
I’ll have to double check the oil.

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74 javelin 401 t-10 3.91 twin grip.
74 javelin 401 998 3.54 twin grip.                            


Posted By: one bad rambler
Date Posted: Feb/12/2019 at 8:00pm
Originally posted by 401fanatic 401fanatic wrote:

ya. I’m gunna have to dig a little deeper. Thanks to all who responded. 
How long are we talking about....More than a week?

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68 AMX 390 4 Speed,68 American,64 American 2 Door Wagon Altered Wheelbase,78 Concord Build 360,727,8.8


Posted By: 401fanatic
Date Posted: Feb/13/2019 at 6:44am
yes more than a week. Is there a diaphragm in the pump that may be bad letting the fuel drain back to the pump ?

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74 javelin 401 t-10 3.91 twin grip.
74 javelin 401 998 3.54 twin grip.                            


Posted By: PHAT69AMX
Date Posted: Feb/13/2019 at 12:13pm
Yes, Diaphragm and Flapper Check Valves.
Mentioned Regulator since other folks having problems after getting new pumps
checked and found they were getting too MUCH pressure, like 12 psi or more,
from a "standard" replacement mechanical pump.  Plus a Regulator may be
"cheap insurance' against possible over pressure and isolate needles and Seats from pulses.
A dude who does a bunch of carbs for folk and has a home-made "engine-dyno" with load,
and does a bunch of youtube videos for his carb customers claims modern gas "likes" only 3-3.5 psi.
Modern fuel, even more so winter blend, boils / vaporizes much easier.




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Link to a http://www.youtube.com/watch?v=MySiKQsmWxU" rel="nofollow - Short YouTube Burnout Video



Posted By: Ramzilla
Date Posted: Feb/21/2019 at 3:59pm
I will be running a STR-11 crossram on my SC Rambler. It still has the original stock fuel line looks like 5/16 inch. Car has been sitting a long time many years. Lines are not rusted nor it underneath of car. Working on brakes and suspension. But already have my STR-11. I would like to leave the original fuel line in place. And add another set of lines alongside the original lines maybe another set of 5/16 inch. Tie both lines together at the tank and run two fuel pumps about 50GPH per pump. Or just run one 100GPH pump tied to both lines. I know some will think I am crazy with these post. And I am no where near this project yet. But like to prepare for it. Want to make sure I get enough fuel to Carbs and only want to do it once. Give me your suggestions please. Ramzilla


Posted By: PHAT69AMX
Date Posted: Feb/21/2019 at 6:20pm
With today's gasoline formulation, might consider a re-circulating Fuel System
with a By-Pass Regulator and a Return Line to the Tank rather than
the usual, like stock, "dead head" type of Fuel System and Pressure Regulator ?
By-Pass Regulators help keep cooler fuel to the carbs and can be easier on the pump(s).
Maybe run that new Fuel Line in 3/8 or 1/2 and have it be the "feed"
and then use the stock 5/16 Line as the By-Pass Return Line ?


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Link to a http://www.youtube.com/watch?v=MySiKQsmWxU" rel="nofollow - Short YouTube Burnout Video



Posted By: Greyhounds_AMX
Date Posted: Feb/22/2019 at 5:56am
Fuel tank is vented properly?

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1968 AMX 390 w/T5


Posted By: Ramzilla
Date Posted: Feb/22/2019 at 7:40am
Good idea about return line. Only thing is that means I have to drop tank to hook up extra lines. Looks like a lot of undercoating around tank and straps. I looked inside with camera tank looks clean because of that I did not think I would need to drop and clean inside. No fuel inside since 1979. I did search about Bypass Regulators. Summit has one that has one inlet two outlets one return and one for gauge. What pressure electric pump would I need to push fuel back out the return line? Carbs only need about 5 to 6 lbs. Not sure exactly how extra pressure pump I need to use for returns. Also I saw post about Vent line so tank does not build up pressure. WOW a lot to think about. Thanks for input. Ramzilla     


Posted By: wheelz
Date Posted: Feb/22/2019 at 8:28am
You dont need electric pumps unless running fuel injection imo. I am running a fuel cell in the trunk to a Fram canister filter mounted to rear frame then 1/2 aluminum hardline to a Robbmc 550 mechanical pump. It feeds both carbs without issues or regulators or return lines


Posted By: PHAT69AMX
Date Posted: Feb/22/2019 at 12:43pm
On the Holley web page they have a rather lengthy Carbureted Fuel System Bypass Regulator write up...

https://www.holley.com/blog/post/selecting_the_correct_regulator_for_your_car/" rel="nofollow - https://www.holley.com/blog/post/selecting_the_correct_regulator_for_your_car/


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Link to a http://www.youtube.com/watch?v=MySiKQsmWxU" rel="nofollow - Short YouTube Burnout Video



Posted By: bobsterfl
Date Posted: Feb/22/2019 at 5:53pm
Lots of great info here.  For what it's worth, I knew that my Javelin would be sitting for long periods of time, so I installed an electric Carter pump near the tank so I would not have to crank the engine too long.  The pump is wired to an "ignition on" source, so I simply turn the key to on for 15-20 seconds to allow fuel to fill the carb, pump the gas twice, and off we go!  I also installed a Mallory pre-luber oil pump for the same reason.  It also comes on with "key on" but has a self timer that shuts off after some number of seconds, and , yes, I can see the oil pressure come up on the gauge.  So, for cold starts, I have both the oil system and the fuel system primed and ready to go.  I don't believe Mallory makes this oil pump any longer, but there are some remote oil pumps on the market for turbo applications that might work.

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Bobsterfl
1970 BBO Javelin
390 - Torqueflight


Posted By: Ramzilla
Date Posted: Jun/19/2019 at 6:25pm
When you get a chance let me know the routing of the oil lines on that pre-luber. And do you need to have check valves installed and where. I have a remote oil filter adapter that I plan on using so it would be easier to plum lines to pre-luber. Thanks in advance.


Posted By: bobsterfl
Date Posted: Jun/24/2019 at 7:38pm
Looks like my reply didn't post so I'll try again.

I drilled a hole in the oil pan (rear of pan near the bottom) and soldered in a pipe fitting.  Then ran hard line along the passenger side pan rail terminated with a short piece of braided hose to the Mallory pump.  I believe the kit had some kind of check valve built in to prevent backflow.  Coming out of the pump another piece of braided hose to the oil pressure port on the block behind the oil filter.  I will try to take a couple of pictures and update this post in the next few days.


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Bobsterfl
1970 BBO Javelin
390 - Torqueflight


Posted By: Ramzilla
Date Posted: Jun/24/2019 at 8:26pm
Thanks looking forward to pictures.


Posted By: Boris Badanov
Date Posted: Jun/25/2019 at 7:48am
Originally posted by 401fanatic 401fanatic wrote:

Fresh 401 modified and about 5 hrs on it now. When it sits for a while I loose fuel pressure prime. It cranks a very long time before I see fuel in my sight glass at the carbs.  New carter street strip mechanical pump. Once I get fuel to the carbs it runs great. Why am I loosing prime all the way back to the tank?


Question, which intake are you using.


My feeling is a HOT (over heated) intake heat stove is to blame.


This issue also makes for other problems on a hot day.


On a summer only engine I always recommend the exhaust cross over be blocked.

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Gremlin Dreams


Posted By: 401fanatic
Date Posted: Jun/25/2019 at 2:56pm
offy duel quad intake. Cross over is blocked. My starter isn’t working and I made the mistake of putting the cheap stainless headers on it which I will not reuse. Saving up for some Doug’s headers. Issue is not corrected yet. Working 6 days a week leaves no time for car. If I have to I’ll put an electric fuel pump on it. I’d just rather not have to. 

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74 javelin 401 t-10 3.91 twin grip.
74 javelin 401 998 3.54 twin grip.                            


Posted By: 990V8
Date Posted: Jun/30/2019 at 1:18pm
Have an electric pump on the 215 in my Land Rover. The ticktick type.
Edelbrock 500 carb on phenolic spacer.
Every time I switch on I hear it ticktick as it refills the carb.
 
On the 327 in my Ambo, I have an electric rotary. Hear it whine as it refills the Holley, then it settles down. Phenolic spacer, crossover closed, but it still does it.
Seems this evaporation thing is just the way it is nowadays.
 
Had an electric rotary on the Rolls-Royce as well. Didn't hear it, so I guarantee if you mount it on rubber bobbins, when the car is running you won't hear it.
 
Ivor


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63 Canadian Ambo 990 V8 327
Lightweight V8 SIII
Shopping Trolley



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