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Old 09-24-2011, 12:41 AM   #1
janderson
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Default lean problem

just ran my car. read plugs. dead lean, stumbling. aeromotive a1000 pump and a4 regulator. my question is about fuel pressure. the guage at the carb is bouncing from 6-9psi when its running. I thought it should be more consistant than that. I have tried 9-15 psi at regulator at pump. Pressure it pretty consistant coming from pump. any help would be appreciated.
Thanks Jason
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Old 09-24-2011, 01:02 AM   #2
trmnatr
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Default Re: lean problem

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Originally Posted by janderson View Post
just ran my car. read plugs. dead lean, stumbling. aeromotive a1000 pump and a4 regulator. my question is about fuel pressure. the guage at the carb is bouncing from 6-9psi when its running. I thought it should be more consistant than that. I have tried 9-15 psi at regulator at pump. Pressure it pretty consistant coming from pump. any help would be appreciated.
Thanks Jason
There are a few things. Your fuel pressure should only be 6.5psi in a FLOWING STATE

Here are a couple things I would consider doing, to help get the pressure set correctly

1) Index the needle and seats. Remove the needle and seat using the 5/8" hex only, then your gonna want to mark the center line of the needle and seat on both sides of the needle and seat on the 5/8" nut like the picture below



Then when you adjust your float levels, you make sure that mark (on either side) is aiming at the center of the fuel line coming into that fuel bowl. The reason is there is a large window in the fuel bowl, and if it is not lined up to the window in the needle and seat, some fuel enters the annular groove in the fuel bowl so it can travel around the needle and seat to the window, when it does this it can cause foaming in the float bowl, so indexing them are simple, easy and helps in the long run.

Your float levels can be on the high side in the back as fuel runs away from the jets, in the front the fuel level can be a hair on the low side as fuel runs too the jets

2) Now when you set your fuel pressure, you will want your fuel bowls LOW on fuel, use a buddy in the car to do this. Have him cut the fuel pump off, hold the engine at 2500rpm, and when the bowls are low, have him turn the pump on so you can set the fuel pressure at 2500rpm with fuel flowing past the needle and seat filling the bowls up for a more "accurate" pressure setting

As to your stumbling, is it foot brake? What is your engine/car set up?
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Old 09-24-2011, 01:14 AM   #3
janderson
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Default Re: lean problem

yeah its a footbrake car. 5k coen converter. 496 solid roller. gm square port heads. turbo 400, 3.90 gears. a2000 pump with a4 regulator. demon 850 carb. it ran 10.70 tonight. stumbled off the line a bit but really stumble on the 1-2 shift. and its hit or miss when it stumbles on the big end. 1.52-1.55 60 ft. plugs looked like they had been dipped in white chalk. no fuel ring to speak of. should the pressure be fluctuating that much at when running?
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Old 09-24-2011, 01:29 AM   #4
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Default Re: lean problem

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Originally Posted by janderson View Post
yeah its a footbrake car. 5k coen converter. 496 solid roller. gm square port heads. turbo 400, 3.90 gears. a2000 pump with a4 regulator. demon 850 carb. it ran 10.70 tonight. stumbled off the line a bit but really stumble on the 1-2 shift. and its hit or miss when it stumbles on the big end. 1.52-1.55 60 ft. plugs looked like they had been dipped in white chalk. no fuel ring to speak of. should the pressure be fluctuating that much at when running?
Have you rebuilt the carburetor? The Barry Grant base plate idle transfer slot holes can become blocked with some gaskets out there

On almost all 4150's I have been able to ET best (On ours, and other people I have helped with Barry Grant's) with 40-45 shooters

Another problem with a BG is the over ride spring becomes too weak, and when you work the throttle you will see the accelerator over ride adjustment nut lift off the arm, to fix this remove the spring and put 2 small washers UNDER on the bottom of the spring and re-install. Throttle wide open, diaphram bottomed out with a screw driver, minimum clearance should be .015"

With the gears, I'm thinking no matter where the power is 5800rpm should be a good shift point, Remember you will see the light at 5800rpm and by time you pull the gear its 6200rpm+

With both engines we ran, we had to set the shift light 400rpm early on one, and 500rpm early on the other

Pressure can fluctuate due to lope of the engine with a one wire alt that doesn't put out proper voltage at idle, thus 2500rpm suggestion
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Old 10-07-2011, 10:08 AM   #5
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Default Re: lean problem

I think I got the problem solved... A2000 pump has to have aeromotive filter to work right. Trick flow filter was restricting it causing pump to cavitate. Changed filter and pressure is rock solid. Going to run it tonight. It should pick up pretty good. Thanks Jason
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