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There are 3 problems on the Street Avengers that cause the stumbles and hesitations:
1. Lean Jetting. The S/A carbs are jetted very lean on the primary side, and extremely lean on the secondary side. Bump primary jetting up about 3 jet sizes and then make the secondary jets 8 sizes larger than the resulting primaries. To save a few bucks on jets, take the jets out of the secondary side and install them in the primary, and then just buy a pair of jets for the secondary side. This gets the carb jetted about right and will do wonders for throttle response and power.
2. Accel pump lever not touching pump cam. I see this constantly on the S/A carbs, and it's really lousy assembly work at the factory: The accel pump lever that connects between the pump cam and the accel pump arm does not ride on the pump cam at idle. The lever is riding on top of the throttle shaft spring and is not touching the pump cam. Only after you rotate the throttle a bit (with no accel pump action) will the pump cam touch the lever and produce a pump shot. To fix this, remove the lever and bend the lever a little more right where you see the "kick-up" bend in the lever where it's supposed to ride on the cam. By giving the lever more of a bend, the lever will not hit the shaft spring and will ride on the pump cam right where it should. This will produce an instant pump shot off idle, and will solve most of the hesitation/stumble issues associated with these carbs. Keep in mind that you will need to re-adjust the accel pump lash adjustment after you bend the arm.
3. Inadequate secondary idle speed setting. On most S/A carbs, the secondary throttle (idle speed) is fully closed. This causes the primary idle speed setting to get cranked up too far in order to achieve a reasonable idle speed, thus exposing too much of the primary transition slot. This, in turn, will cause an off-idle stumble due to lack of transition fuel enrichment as the throttle is opened. The primary and secondary throttles should be open the same amounts at idle - they should be balanced and see equal airflow.

Forget about swapping pump cams and accel pump nozzles - that's not the issue, and it won't solve your problems. Fix the pump lever geometry instead...
so in other words the the name of the game her is product control. holley failed with these.
 

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There are 3 problems on the Street Avengers that cause the stumbles and hesitations:
1. Lean Jetting. The S/A carbs are jetted very lean on the primary side, and extremely lean on the secondary side. Bump primary jetting up about 3 jet sizes and then make the secondary jets 8 sizes larger than the resulting primaries. To save a few bucks on jets, take the jets out of the secondary side and install them in the primary, and then just buy a pair of jets for the secondary side. This gets the carb jetted about right and will do wonders for throttle response and power.
2. Accel pump lever not touching pump cam. I see this constantly on the S/A carbs, and it's really lousy assembly work at the factory: The accel pump lever that connects between the pump cam and the accel pump arm does not ride on the pump cam at idle. The lever is riding on top of the throttle shaft spring and is not touching the pump cam. Only after you rotate the throttle a bit (with no accel pump action) will the pump cam touch the lever and produce a pump shot. To fix this, remove the lever and bend the lever a little more right where you see the "kick-up" bend in the lever where it's supposed to ride on the cam. By giving the lever more of a bend, the lever will not hit the shaft spring and will ride on the pump cam right where it should. This will produce an instant pump shot off idle, and will solve most of the hesitation/stumble issues associated with these carbs. Keep in mind that you will need to re-adjust the accel pump lash adjustment after you bend the arm.
3. Inadequate secondary idle speed setting. On most S/A carbs, the secondary throttle (idle speed) is fully closed. This causes the primary idle speed setting to get cranked up too far in order to achieve a reasonable idle speed, thus exposing too much of the primary transition slot. This, in turn, will cause an off-idle stumble due to lack of transition fuel enrichment as the throttle is opened. The primary and secondary throttles should be open the same amounts at idle - they should be balanced and see equal airflow.

Forget about swapping pump cams and accel pump nozzles - that's not the issue, and it won't solve your problems. Fix the pump lever geometry instead...
so in other words the the name of the game her is product control. holley failed with these.
Great post! I wish you had made it about 6 years ago, it would have saved me a lot of time. I had to learn all these things the hard way on a 670SA I ran on a 4V cleveland.
 

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The best fix is to throw it away, I could have bolted a canned ham to my intake and got better performance out of it. I finally bit the bullet, bought a 4100 off ebay, rebuilt it, and now I have got a solid performing, reliable carb. The street avengers are emissions carbs, way too lean, particularly on the outdated idle circuit and the idle circuit is non adjustable without drilling. To top this off their tech support acts like they have never heard of any problems with them, but if you google these carbs there are numerous forums that address these problems over several years, in fact, since their conception.
 

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