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Edelbrock Carb Question

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Old 12-07-2018, 10:12 AM
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Edelbrock Carb Question

I have a 77 F150 351M, C6, both recently re-built. I hesitantly dropped an Edelbrock 1406 carb w/electric choke on it. Always seemed to run a little off, have an adjustable regulator set for 5psi, every once in a while it would miss, hesitate on acceleration, and surge at highway speeds. Also, the strangest is, I would activate the choke and the carb would flood itself out????? I lowered it to 3.5psi yesterday and it seems to have gotten rid of the miss, surge and hesitation on acceleration. To me sounds very low, does anyone have a suggestion on what the pressure should be? I will check after work today and see if the choke flooding is still an issue. But it seems to run much smoother
 
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Old 12-07-2018, 11:17 AM
mark-guiver
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The only thing I can think of is the Edelbrock carbs only require 6 psi or less or they will be over fueled. I had the same issue with mine due to the Carter mechanical pump putting out 9 PSI. That was stated in the specs and measured with a gauge. I installed a regulator and played with the pressure until it runs great now. Mine is set at a little over 4 and that seems to be what it likes. It will actually run on just gravity pressure as I had to do when the old fuel pump failed a couple of years ago. The diaphragm was degraded from the ethanol in the gas these days so now I use pure gas most of the time. If I have to use E-10 gas I put Lucas fuel treatment in with it. I buy the Lucas in a gallon bottle and add 6 oz's per tank.
Mark.
 
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Old 12-07-2018, 11:39 AM
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I guess that was the issue, I will see how it runs after I get off work. I just bought a bottle of the Lucas Ethanol treatment, not the gallon, for my snowblower and lawn equipment. I think I will put some in my older vehicles as well, probably makes sense. Thanks.
 
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Old 12-07-2018, 07:20 PM
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I've had a 1406 on a street rod, and I've had the 750 CFM version on my dent for 15+ years. They need about 5-5.5psi to run properly. I suggest getting a wide band sensor and gauge to take guess work out of tuning. They are pretty cheap on eBay now.

That said, I just purchased a summit carb to replace the edelbrock because I've had enough of the chokes on those things. They just don't work consistently. One day, they trip off too quickly. The next, it next it never trips. I've had 4 of these carbs, and they all were that way. It's frustrating.
 
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Old 12-08-2018, 09:23 AM
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Hesitation on accel, and surge at highway speeds sounds like lean condition. At normal acceleration and cruise you're probably making about 12-20" of vacuum. That's not enough vacuum drop to lift the metering rods on an out of the box Edelbrock carburetor. Try this... Repeat the same conditions that give you problems. Then accelerate a little harder to drop vacuum, and see if it gets past that hesitation. If that works, the easiest thing to try first is to change the metering rod step up springs to the next lighter springs. This will allow the rods to rise at a higher vacuum, giving you more fuel when it's needed. If that improves but doesn't fix it, look at changing rods to smaller diameter to allow more fuel flow. Those steps are easy. After that you'll need to pull the top of the carb to change primary jets. Edelbrock website has detailed tuning charts for your carburetor that will help you. One last thing, I tell everyone to install a Air Fuel Ratio gauge. Vacuum gauge too. It takes all the guess work out of tuning a carburetor.
 
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Old 12-08-2018, 09:13 PM
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I use a 1405 and manual choke. I bought the kit of various metering rod springs, etc . FPR set at 5.5 psi.
 
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Old 12-10-2018, 10:11 AM
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Thanks guys, it seems to be running fine for now but once it warms up a little I will try changing the springs and jets, my last resort will be to change the choke to manual, I have that setup on my Fairlane and that runs perfect.
 
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Old 12-10-2018, 11:37 AM
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In general, the Edelbrock carbs with manual chokes are set up rich out of the box because they are more intended for racing. The Edelbrock electric choke carbs are set up lean out of the box because the feeling is they will be used for cruising and daily driving.
Bucking and surging on the highway sounds like lean surge to me.
Edelbrock has VERY SPECIFIC instructions for leaning or richening the mixture. They are quite helpful and take the guesswork out of changing the mixture, showing increases or decreases in IIRC half steps. You have jet, metering rod and spring, three chances to mess up. So using the chart is the smart thing to do.

The carburetor only needs enough pressure for fuel to flow through the needle and seat and keep the float bowl full. It could most probably do it with 2.5psi. Carburetors are not fuel injection. All the carburetor needs is fuel flow to keep the fuel in the bowl up to the correct level. If the float can hold against more pressure, then the carb will work at that pressure. If the pressure pushes the needle down against the float, lowering the float, pressure is too high; Keeping the fuel level at the right height is important because it can change air/fuel ratio when the height of the fuel column changes.

R.
 
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Old 12-10-2018, 03:19 PM
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Originally Posted by njdevil77 View Post
Thanks guys, it seems to be running fine for now but once it warms up a little I will try changing the springs and jets, my last resort will be to change the choke to manual, I have that setup on my Fairlane and that runs perfect.
I didn't mention it before, but I wouldn't have an electric choke carburetor. E chokes can (and almost surely will) ruin your day. Manual chokes never get out of adjustment. And you have full control of it.
 


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