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Discussion Starter #1
OK, I'm starting from scratch. I have a Holley 670 Street Avenger with a 0.035 discharge nozzle and a primary jet of 67 with an orange in color cam. Standing next to the engine and revving it to WOT by hand, there is a stall....and then it catches up and revs (eyes are watering by now). Test driving the car....major hesitation/stumble in reverse and 1st, gotta keep up the revs to take off, surges/bucks shortly after shifting to 2nd. It should be noted, it did the same thing with a 0.031 nozzle and a 68 primary. 10" of vac at idle and installed a 4.5 PV. Pertronix/Flamethrower, initial timing at 16. Comp Thumper with a duration at .050 of 227/241, 350, mid 60's camel hump heads, not a very high comp shortblock (I think it's a crate shortblock with dish pistons), M20, 3:42's. Should I throw the carb in the trash and get a BG or Edlebrock "Just bolt-on and go"? Just kidding....help me adjust this beast!
 

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The stock #65 primary jets in my 670 Street Avenger were way to lean. I had to go all the way up to #73 primary jets to eliminate the stumble and surge.
 

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I have a 670 and had a similar situation also. I put on an Echlin VC1810 and adjusted the timing, adjusted the carb with a vacuum guage and 90% of problem solved. I do believe a 570 would be adequate for me. Perhaps not your problem but following John Hinkley's advice sure helped. When time allows I'll bump up the jets and see if that helps with the "out of box" claim.
 

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Discussion Starter #4
If I try a richer primary, do I have to change the secondary? Can anyone recommend a primary and secondary combination? Thank you Scott and Steve!
 

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Get yourself some #70’s, #72’s, and #74 jets as well as some gaskets. Start with the #74 primaries. If this fixes the stumble and surge drop down to #72’s. Keep reducing jet size until the lean symptoms return, then go back up two jet sizes.

The secondary jets won’t have any effect on either a stumble during a normal takeoff or a surge at part throttle. I would either “square jet” your carb with the same size jets both primary and secondary or go with slightly fatter secondary jets (one or two sizes bigger than the primaries).

Get the primaries right before you change the secondary jets.
 

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What about a bigger pump shot? If the car is stumbling and falling flat when the throttle is snapped open.....Plus, swapping out the cam for a bigger cam takes only a couple of minutes and you can see what you get immediately.

Holley makes a kit with a bunch of different cams.

alan
 

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Discussion Starter #8
I tried a 35 nozzle and it made it worse. I also bought a pump cam kit and installed the blue cam....no difference. I am now going to put the 31 nozzle back in and change the primaries to 73 from 68. I'm experiencing a right "off-idle" hesitation at low rpm's.
 
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