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Thread: Need some carburetor help.

  1. #1

    Default Need some carburetor help.

    Iím fairly inexperienced with carburetors as far as diagnosis goes. So hereís whatís going on, the setup. My dadís got a 66 Mustang GT with a roller 302 in it. Thereís a Barry Grant Six Shooter setup on it. Iím 90% sure thatís what it is off the top of my head anyways.

    The problem, it runs great just driving around town, or cruising. But he does AutoX in it too. Itíll make a couple runs fine, then after everything is heat soaked it starts to cut power and stumble. It mostly happens in hard turns, but is better with higher RPM. Heís replaced and rerouted all of the fuel lines and fuel pump as well. It did get slightly better with just that, but the issue is still occurring regularly.

    The choke butterfly is locked open, so we know the choke isnít closing and causing it. It still feels like itís a heat issue. The car does have a ram air hood on it though, so I could be wrong...itís happened before. The fuel pressure and volume is also correct, that was verified. It comes off the line hard, and the timing and everything was dialed in on a dyno too.

    I think thatís all the information I can remember right now. I attached a couple pictures of the car to show the hood as mentioned, and also for the attention. Iím just hoping someone that knows about carburetors, maybe even these Barry Grantís can help shed some light. Thanks in advance for any and all help.

    Fuel line is 3/8" braided stainless, it's regulated to 7 psi (on the dyno, hasn't been checked while driving yet), carbs have sight holes to see fuel level, also has a return setup to bleed off excess pressure. The pump in and external electric vane type pump by the stock fuel tank. Line has been routed away from anything hot.

    The carbs are supposed to be baffled according to the information I've seen. They're basically Holley 2 barrel 250 cfm carburetors with the bowls on the rear of them which are set up to run off the center carb until the progressive linkage opens up the front and rear carbs.

    Since the upgrade of the fuel lines the issue has gotten better. It runs great in a straight line and even in a slalom, and cruising, but then bogs out coming out of a hard sweeping turn.

    The fuel is 75% 91 mixed with 25% 110 race gas.

    I think I got everything, let me know if I missed something though.

    I found a stock photo of the setup if anyone isn't familiar with it already. Apparently, these were very popular with SBC and rare for SBF so finding a picture was tough.

    Click image for larger version. 

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  2. #2
    Join Date
    Jan 2010
    Brisbane, Australia


    Does sound heat related. The primary carb uses fuel at a faster rate at part throttle. You have two secondary bowls absorbing heat from low use at part throttle. They also all face backwards, which is wrong really, especially all of the bowls, in comparison to 2x4 barrels where 2 face forward, and 2 face backwards. So if it goes hard normally, and then this starts happening, look at some heat shielding between the fuel bowls to manifold, more cold air flow over the carb bodies etc. Gary
    Regards, Gary

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