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Help Needed, KR Convertible on the Dyno, CARB Issues

Discussion in '1965-1970 Shelby Mustang GT350 & GT500' started by mherman2, Aug 29, 2008.

  1. mherman2

    mherman2 Well-Known Member

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    I just had the correct "AB" carb rebuilt by Pony Carburetors and the C6 transmission rebuilt here in San Diego and the correct torque converter put on and an original water pump, and correct smog pump (minus guts). All correct pulley's etc... it is brand new looking and all correct under the hood for an AC car.

    The rebuilt is .30 over and only has 200 miles on it at this point. I put the full rebuilt specs below at the bottom of this.


    We put the KR on the Dyno and immediately sensed a fuel delivery issue. It was going lean on the top end at 4500 rpm's+. We checked the nozzle sizes. Pony Carbs put 66's on the back and 70's on the front and a 29 up front. ????????

    This is the correct AB carb for a KR auto. Why would someone like Pony use such small nozzle sizes for a rebuilt/replated carb for a 428??? What was factory spec for nozzle sizes on these carbs???

    After replacing the nozzle sizes at JBA (J Bittle) here in SD with something larger, we ran it again and picked up some more horsepower but we are still below well where my 428 PI is at on my 67 GT500. Both engines were rebuilt by the same shop. I understand we need some more break in miles on the 68 but it is obvious there is a fuel delivery issue. It's not the pump (newly rebuilt Carter X). It's not the timing (36). We are only getting 222 HP at the rear wheels which when multiplied by .75 gives you 296HP at the fly wheel. The secondary's are kicking in when the should. Mike Mulcahy mentioned about checking the float levels in the rear??? ( I am not familiar, still learning).

    Specs on rebuilt below:

    # L2303NF .030 Forged TRW Pistons (stock replacement)
    # 160308 SIG ERSON HYDRAULIC CAMSHAFT KIT (cam, springs, retainers, locks) .510 lift intake & exhaust/280 Duration (.295 @ Cam, intake opens 34 btdc/closes 66 abdc, exhaust opnes 74 bbdc/closes26 atdc) Cam timing at .050 Intake 2 btdc/closes 32 abdc max lift 105 atdc 214 duration, Exhaust opens 42 bbdc/closes 8- atdc max lift 115 btdc 214 duration
    # ALL FEL-PRO GASKETS
    # Melling H57HV Oil Pump
    # F6212 Ferrea Stainless Intake Valves
    # F6215 Ferrea Stainless Exhaust Valves
    # 9-1108 Cloyes Timing Set
    # Pioneer Brass Freeze Plugs
    # Motorsport Oil Pump Drive, Windage Tray
    # Clevite Cam, Rod, Main Bearings
    # Factory AMK Bolt Kit
    # Customer supplied Factory Holley Carburetor
     
    Last edited by a moderator: Mar 7, 2010
  2. Seaweed

    Seaweed Well-Known Member

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    Have a 68-Pi, 7-8 years ago sent the carb. Holly 4150 to Pony carbs. Did a nice job, but had to up the jets sizes quite a bit. 73's & up if i can remember, the car runs awsome. At the time on the dyno it would lean out & remembering him saying , can't let the car go out of here in that condition.--S.
     
  3. patty.dilabio

    patty.dilabio Well-Known Member

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    Hi to Mike and all: I have a possible solution,or at least something else to check.Drain the tank of fuel.Remove the sender assembly.Replace the filter that slides on the pickup tube.Still available from Ford,and often overlooked as a solution for fuel flow problems.The stuff that it collects slows down flow--the fuel pump cannot draw adequate fuel through a restricted filter,and cannot supply a thirsty carb under load.Many people just dont look here first,and if you haven't I would.Hope this helps!:)
     
  4. Bob Gaines

    Bob Gaines Well-Known Member

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    I second this possiblity. I had a friend with a similar issue recently and that was the problem. The solution in his case was a new tank and a new fuel sender sock .
     
  5. mherman2

    mherman2 Well-Known Member

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    Thanks guys, we are looking today and I will let you know.

    BTW, I got my 67 GT500 dyno tuned as well at JBA here in San Diego. We have about 275hp at the rear wheels which equates to about 366hp at the fly wheel (275/.75=366 ). All completely stock.

    It was running way rich at 10.5, moved it up to 12.5 and found 45 more hp.
    Mike
     
    Last edited by a moderator: Mar 7, 2010

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