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Holly 2X4
Can any one advise me on how to tune my holly 2X4 carbs?? (570 cfm BJ/BK vacume secondaries) see my gallery.
I just fired the motor on a test stand for the first time and they seem to pop & back fire any advise on how to adjust the screws on the sides and or the linkage will be very much helpfull!! Thanks, Mike |
Here is how I do it. Step #1 is, if you can, run each carb on a known, good running motor separately and adjust them so you can be sure nothing is wrong with each carb. (This way if one is bad, you don't have to figure out which one it is). Hook up a vacuum gauge to read Manifold Vacuum. Disconnecy throttle linkage from both carbs first. Adjust idle mixture screws on primary carb (Front) to reach smoothest idle and highest vacuum. Then adjust the idle speed screw to set idle. Now adjust idle mixture screws on rear carb the same way. I always go back and repeat the process at least twice on both carbs. I also back off on the idle speed screw a little on the carb I am not adjusting on at the time. With the popping, it does sound like you may have a vacuum leak. Be sure and check float levels several times during your adjusting because they could change during adjustments. After all of this , re-connect the throttle linkage to the primary carb and adjust linkage. Now re-connect linkage to the rear carb and adjust to leave about 1/8" in slot on rear carb. (Front opens- then rear starts opening after front travels 1/8".) Now all of this is just a starting point, because every engine is a little different. I hope this helps. If I can tell you more, email me. Later, David.
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