Ford 7200 variable venturi carb swap on 81 LTD Wagon

Discussion in 'Domestics' started by CHUCK06, Mar 12, 2013.

  1. CHUCK06

    CHUCK06 Full Member

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    I have a 1981 Ford LTD station wagon, 302 engine, A/C. A/T. It has a 7200 VV carb. I found a said to be PRO rebuilt 7200 vv carb on ebay and was the only bidder, That carb is on it's way, but who knows if It will work. From what I know, these carbs are not easy to rebuild, finicky and commonly are replaced with a regular motorcraft 2bbl carb. I bought the recommended replacement, Its here now and I'm hoping someone who has done this swap may be able to fortify me with a little knowledge. And yes, the carb that is on the wagon has issues so the replacement is necessary. Thanks for any direction.
     
  2. CHUCK06

    CHUCK06 Full Member

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    The carb I ordered is supposed to be the Ford service replacement. motocraft 2150? I think......I bought it from National Carburetor, the part number is ND-2735.
     
  3. opelgt

    opelgt Hero Member

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    Swapping a carb out is fairly easy since it is the same type of carb. Not sure what kind of " knowledge" you are looking for. Just disconnect the fuel line, the vacuum lines and the linkage. Remove the four nuts holding the base and remove. Be sure to replace the base gasket with a new one and install the replacement carb.
     
  4. CHUCK06

    CHUCK06 Full Member

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    Swapped the carb yesterday, I was just worried, I scanned a lot of forums and there was a great deal of hype and confusion among others who did this swap, about swapping for the duraspark II ignition system and such. The carb is on, the choke works perfect. The kickdown hook up is a little different, so I need to figure that out. And though it starts and runs smooth. There is a dead spot and will stall if you are too light on the pedal. Too lean or rich?
     
  5. al daniels

    al daniels wrench

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    does your distributor have a vacuum advance unit or is the timing electronically controlled?
     
  6. CHUCK06

    CHUCK06 Full Member

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    It has a vacuum advance. So I guess its the EECII and Duraspark II setup. The carb that I replaced the vv 7200 with is a aftermarket motorcraft 2150. It is running great and started right up this morning without pumping the gas. Just that dead zone is the only issue. I guess i will fog the engine this evening and check again for vacuum leaks. My grandfather had a 50 ford with a 302 from a 79 bronco, his car was always like mine is now, with that dead zone. It stalls out on take off unless you gently accelerate for a second, let off then hit it again being sure to go pass
    the dead spot.
     
  7. NickD

    NickD wrench

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    Had a 302 CID Ford similar to yours, distributor was strictly vacuum, no centrifugal advance, and initial timing had to be set with the vacuum line disconnected as I recall. Vacuum line went to the venturi vacuum, vacuum would increase near linear with engine speed. You should have a venturi port on your new carb. The size of that venturi port did make the difference in the amount of advance.

    [​IMG]

    Wow, carbs are expensive now, see this one doesn't even have the choke cover, memory is bad, don't recall if its manifold heater or electric.

    [​IMG]

    What I recall is that the choke had to be set as rich as possible, but still wide open when the engine reached operating temperture. If set any leaner, engine would kill when you hit the gas until completely warmed.
     
  8. CHUCK06

    CHUCK06 Full Member

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    The carb i put on, has electric choke. I drove the car for over 45 minutes and still had the dead spot. I hooked the vacuum line for the advance at the same location as it was on the vvc 7200. I will let you know what I find out tonight.
     
  9. NickD

    NickD wrench

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    Can also be accelerator pump issues, holding the choke opened, and manually operating the throttle can you see a healthy spray of gas in the venturis?

    Can't see on the photo above, some have different holes so you can get more spray.
     
  10. CHUCK06

    CHUCK06 Full Member

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    The photo looks like a variable venturi carb, that is what was originally on it. The carb i installed is a brand new motorcraft 2150. Its different than the the carb in the photo. When the other carb was on it, it would not cold start without priming and with gas and holding the slide closed for a few minutes, then let the car warm up for another 10 to 15 before driving and would stumble at cruising speed.
     
  11. billr

    billr wrench

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    Does this have an EGR valve? Maybe try disabling that temporarily, see what difference that makes.
     
  12. al daniels

    al daniels wrench

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    try hooking your vacuum advance to manifold vacuum rather than venturi vacuum.if this helps you might have to retard your base timing to avoid detonation.
     
  13. CHUCK06

    CHUCK06 Full Member

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    Yes it has a EGR valve, seems to be working fine, I have not tried driving with it disconnected but i will try that tomorrow. If I'm under the hood and hold the throttle at the dead spot and close the choke a little, it picks up, so It seems to be lean, but only at that spot, which also happens to be the same throttle position at cruising speed. Exhaust smells rich though. smells pretty gassy at the breather tube, Maybe some positive crank case pressure,,,,,dun dun dunnn. I sure hope not. Also I will hook up manifold vacuum to the advance and see what that does, The linkage on this new carb is not compatible with my overdrive kick down, is there a kit for this or do I need to get creative.
     
  14. NickD

    NickD wrench

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    Come on, so when you hit the gas, and need spark advance it will retard? Does the vacuum advance work smoothly or is the distributor a pile of rust?

    EGR certainly cannot be overlooked, in these earlier models, no sensors were used, just a thermal switch and again to the venture vacuum to crack it open at about 1700-1900 engine RPM. While the EPA states its to reduce NOx's emissions. It does, its prime purpose is to reduce combustion chamber temperature. Unleaded gas burns at around 500-700 degrees hotter than leaded gas did. First sign of a failed EGR system is burnt out exhaust valves.

    Did you ever do a compression check on this thing? Always the first step.

    Slightly off topic, aviation never did use leaded gas, low RPM high torque engines, for the high performance engines, water injection was employed. Considered too difficult for the average car driver, so was blessed with the EGR valve. It does effectively reduce the CID displacement of our engines by about 30%. Some playing around with using ceramics for key engine components, but that never got off the ground. Earlier exhaust valve closing is far more reliable, but also more expensive for a consumer grade vehicle. Our vehicles are consumer grade, by the way.

    If everything is right, this engine will run fine, question is, what is the problem? Again would start off with a compression check, also like to use a real accurate oil pressure gauge, just to know the engine is okay.
     
  15. al daniels

    al daniels wrench

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    nick,with the vacuum advance hooked to venturi vacuum it does nothing when you step on it.not until the vacuum comes up does it do any advance.also take into account that the vacuum advance as it is traditionally used is only for fuel economy and has little or nothing to do with performance. older chevies had a valve that fed manifold vacuum to the vacuum advance until you stepped on it and then changed to venturi,giving a better accel. off the line. this isnt just some crackpot idea ive come up with,it actually has some basis in fact. at any rate it is quick to try it and see.
     

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