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Hello all this is my first post here. I recently bought a 81 Bronco with a 351M in it. It was missing pretty bad and would barely idle so I did a full tune up on it. Dist cap, rotor, plugs, wires, fuel filter, oil and filter change. I have also replaced the vacuum advance as the diaphragm was blown on it.

The issue I am having with it is a hesitation off idle parked or in gear accompanied by backfires from what I believe to be the exhaust, from the source of the sound. If I am already the slightest bit into the accelerator then the hesitation is not there and neither is the backfiring. I can continue accelerating most of the time up to higher speeds such as 60-70 mph without a backfire as long as im not too heavy into the pedal. It will backfire under load though; for instance trying to sustain 60 mph up a hill.

This is the first carb equipped vehicle I have owned so they are pretty foreign to me. The vehicle does have a 4 bbl intake manifold and a holley 4160 on it. So far I have checked the timing and set it to 10 BTDC. The timing mark isnt jumping around at idle and I was told that means the timing chain is more than likely ok. Checked that the mechanical and vacuum advances are working with a timing light (just visually made sure that the timing mark was moving when revved and when vacuum was applied to the vacuum advance at idle. I set the idle mixture screws with a vacuum gauge (the vacuum never changed much though so I basically screwed them in until the idle got rough then backed them off 1/2 a turn.) Other than that I'm not sure how or what to adjust on the carb. It doesn't have the sight glasses or holes for the floats so the only way to check them is to pull the whole cover off which I haven't done yet.

I purchased a Holley carb rebuild kit, but am having difficulty finding the time to pull the carb and let it sit in the dip overnight before I rebuild it. My days off are always split and I typically work late into the night before them. Will rebuilding the carb fix these symptoms or am I needing to change jets or something? Is there anything I can do or adjust to allieviate the symptoms until I can find the time to rebuild the carb?

Thank you for taking the time to read through this and offering any insight you may have.
 
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