Engine Need Some Help With Timing/carb Settings

Discussion in 'Classic Mustang Specific Tech' started by supeg, Aug 20, 2013.


  1. supeg

    supeg New Member

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    Hey guys. Have had my 1973 Mustang Mach 1 for approx 10 years. Last couple of years I have been really busy with my new family and have barely had any time to take it out at all. It seems to have issues with Timing and Carb (Runs real rich).

    I used to take my Mustang to Classic Car shops in the past for stuff like this but they have gone under. I am pretty mechanically inclined but more towards the newer stuff, but eager to learn.

    Here are the specs on the Car.

    1973 Mustang Mach 1
    351C Q code 4V .30 over bore
    Aftermarket Comp Cam
    Long Tube Headers
    3.0 inch exaust with Flowmasters
    Holly 750 Double Pumper
    4.11 Rear end
    Manual

    I have included some pictures at the bottom of this post showing some of the specs of the items in the vehicle.

    Basically I need help setting the Carb and the Timing. I have never done the timing and will be buying a timing light. Do I set it at Idle and what degree's do you guys think would work and how do I actually do it.

    The Car runs rich as well and would like some help with tuning the carb.

    I apprecate any and all help you guys could give me. Again, I have a young family and cannot really afford a shop so trying to learn and figure this stuff out on my own.

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  2. woodsnake

    woodsnake Active Member

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    As there are not a lot of electronic options like there are with an OBD II car, you will need a good timing light, and a vacuum gauge.
    Do you already have those, or can borrow them? I would start with a base line timing of 10 degree's initial advance, with the vacuum advance unplugged. You will need to use the vacuum gauge to adjust the air bleeds on the car, to get the highest number of inches of vacuum at idle. Then you can start to fine tune. I would think an idle speed around 950 RPM in park, 750 in gear, would be a good place to start....
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  3. brianj5600

    brianj5600 Active Member

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    What distributer are you using? Do you know how much mechanical advance in it? This site tells how to modify a duraspark mechanical advance. http://www.reincarnation-automotive.com/Duraspark_distributor_recurve_instructions_index.html I like a little more initial, 16-18 degrees and set mechanical to get desired total advance. I don't know what those motors like. I would guess 36-40 degrees with the open chambers? Definately don't take my word on the total number.

    A lot of rich idling Holleys are a result of the primary throttle blades being open too far. Over exposing the transfer slot will cause it to idle and cruise richer which is a problem when added to the larger than neccessary idle feed restricter used in a 750dp. You can tune around the IFR if you get the transfer slots right. Google "transfer slot picture". Get the primary throttle blades set right and use the secondaries to adjust idle. You can remove the secondary idle screw from the bottom and put it in from the top. I makes it easier to adjust, but you have to turn the engine off to adjust it.
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  4. rbohm

    rbohm Founding Member

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    since the 73 351c has open chamber heads, you want to limit the initial timing to 10-12 degrees btdc. you also want to get as close to 32-34 total timing as possible.

    in regards to your fuel mixture, get the idle speed and mixture right first, woodsnake i think hit the nail on the head with the idle speed suggestion. if you cant get the mixture properly leaned out at idle using normal methods of playing with the mixture screws and jetting, you can drill a small hole in the primary throttle plates, no more than about 1/8", to let more air in. that has the effect of leaning out the fuel mixture at idle, and smoothing out the idle speed at the same time.
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  5. supeg

    supeg New Member

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    Here are some more pics

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