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I've been trying to tune my BC Rochester on my 63 Nova and have not been able to prevent an off idle stumble, hesitation and occational backfire. The accelerator pump is good and I've adjusted everything to factory specs to no avail. One other question, does anyone know if the automatic trans carb's throttle body has a hole or slit inside the vacuum port for the distributor/trans? My carb has a slit and I think it might need the hole to give the distributor/trans full port vacuum. Any help would be greatly appreciated.
 

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See if the butterfly linkage bushings are worn. If so, you are getting a vacuum leak and will not be able to adjust it right. Wiggle the shaft. There should be no play. If that is tight, check your distributer shaft and see if there is any play in it, if so, you need to fix that or you will never get it adjusted right either. I ran into the same trouble with my 62 and after fixing those two problems, it starts easy, no hesitation, and no backfiring.
 

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63' carb problem

Thank's for reply! I have a new distributer so I know this is not the problem! The butterflys don't feel that to lose. Any more suggestions??? Would be greatly appreciated. Can anyone tell me what is the differents between the automatic and standard transmission carb. Abel
 

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I had the same problem on mine a few years ago. What we found was the check ball in the off idle circuit was leaking fluid past it. Inside the carb you should find a check ball that is held down by a spring. In the transition between the idle and off idle circuit this area where the ball/spring is located will open and allow fuel in. If this well is empty, you will end up with a stumble off the line. I went through 5 rebuilt carbs before giving up and found a NOS piece.

you have the carb apart, put some solvent or fuel in this well and see if it trickles through, if so the seat may be bad.

Another thing to consider is the vacuum advance may be coming in too early.

Tim
 
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