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  •  » Adjust A/F when adding power brakes?

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    6/26/2013 9:18 PM  #1

    malakabob
    Unregistered

    Adjust A/F when adding power brakes?

    So i have a 69 mustang with a edelbrock 1406 carb on a 302. i recently installed power disc all the way around, system bled fine, works fine, and certainly stops fine. my issue is that when my brake booster is not connected to my carb (i.e. i plug that vacuum port) the car starts up easily and idles as desired between 900-1000. when i rev the engine it responds great. now, when i connect my brake booster, which is brand new, to the carb the car is more difficult to start (usualy requires a little more gas to turn over). once it does start, it will idle briefly around 1200 then usually start to fall off unless i give it some more throtle. sometimes it will idle around 1200 to 1300 but then will either fall off oer randomly jump and hold an idle around 2k to 2.5k.

    Now, i know an irratic idle is typically the result of a vacuum leak. so i sprayed carb cleaner around the check valve on the booster, along the vacuum hose, and where the hose connects to the back of the carb but saw no changes in idle speed. i also tried swapping the vacuum hose from the carb to the boster but the irratic behavior remains.

    I suspected the brake booster's check valve may be bad, so i connected a vacuum pump to the booster, and it built and held a vacuum quite well. once the vacuum was built, i stepped on the brake pedal and watched the vacuum fall over the course of a few pumps.

    Based off the fact that when my booster isn't connected my engine works just fine i'm fairly confident the issue stems from adding the booster to the system (since it is the only thing changing from a motor running fine to one that doesn't). With the engine running (as tempermental as it may be), my brakes work just fine and my booster's check valve also seems to work based off my vacuum test, so i'm hesitant to say that the booster is actually bad. Since i've also checked and swapped the vacuum line for good measure, i'm pretty stumped on this one.

    Since i've never converted a car to power brakes before, i'm curious if i need to readjust the fuel air mixture when i add power brakes because of the increase in vacuum? it's really the only thing i can think of.

    Thanks for any help you can offer me

     

    6/26/2013 9:30 PM  #2

    darren
    I FYI 24-7

    Offline

    From: Wentzville Mo.
    Registered: 4/05/2013
    Posts: 460

    Re: Adjust A/F when adding power brakes?

    adding power brakes should not need a change in A/F ratio ever.
     

     

    6/26/2013 10:03 PM  #3

    steve s.
    FYI FORD Member

    Offline

    From: Nashville TN
    Registered: 5/10/2013
    Posts: 60

    Re: Adjust A/F when adding power brakes?

    i just added 4 whl power discs to my 69, also 302 with no issues. only thing i see different is my hose from the booster is connected to the vacuum "t" in the manifold & not the carb. my pcv is connected to the port on the back of the carb.

     

    6/27/2013 6:08 AM  #4

    MS
    Forum Originator

    Offline

    From: Canyon Lake, Texas
    Registered: 1/24/2013
    Posts: 11,734

    Re: Adjust A/F when adding power brakes?

    A non-leaking booster should not make any difference to the carb.  It sounds like you have done some pertty good troubleshooting with this.

    Where do you have the vacuum line connected?  There should be a vacuum port on the intake manifold that intersects two runners.  (some may only go to one runner)  Connect there, not at the carb.

    If you clamp the hose shut, does the carb go back to normal operation?

    Does your brake pedal allow the booster to come to full rest position, not holding it partially open?  What booster and pedal do you have?

    Try spraying the starting fluid under the dash at the rubber boot, where the foam rubber or felt filter is located around the booster input shaft.  If the booster was leaking internally, THAT is where it would be taking air in.

    Money you enjoy wasting is NOT wasted money... unless your wife finds out.
     

    6/27/2013 6:33 AM  #5

    malakabob
    Unregistered

    Re: Adjust A/F when adding power brakes?

    thanks all for the reply.

    Steve, the vacuum line is connected to the vacuum port at the lower rear of the carb, which edelbrock recommends to connect the brake booster connection.

    i'm fairly confident that port on the carb is below the throttle plate so i don't think it should make a difference if it is connected there or on the actual manifold, but i will add that to the list of things to check. just in case

    i have not tried to disconnect the hose from the booster and plug the end to see if it still acts funny, but i supposed that's one more thing i could try to verify the hose.

    My pedal is the longer, power brakes pedal. i had to replace it when i added the booster. and yes when the car is running the pedal is still able to return to the normal location. do you think the booster push rod could be adjusted improperly, and if so, would that even cause vacuum leak like symptoms?

    The booster itself is a stock style cardone reman. i thought about spraying the fluid under the dash like you suggested, but i will have to do that this evening since i don't get paid to work on cars.

       •Thread Starter
     

    6/28/2013 11:04 AM  #6

    MS
    Forum Originator

    Offline

    From: Canyon Lake, Texas
    Registered: 1/24/2013
    Posts: 11,734

    Re: Adjust A/F when adding power brakes?

    Don't disconnect anything to stop the vacuum from going through the hose.  Unless you used an A/C hose, you can usually just put some vise-grip pliers across the hose for a temporary blockage test.

    Money you enjoy wasting is NOT wasted money... unless your wife finds out.
     

     

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