lars

I keep running into Holley Street Avenger carb problems related to off-idle stumbles and part throttle hesitations. I've seen these issues on the Tuning for Beer Tours, and I just had yet another SA carb (the 4th one with these issues) sent to me with these problems, so I thought I'd share the issues and solutions with you.

There are 2 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.

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...

7t2vette

Been there, and done that! I still remember wondering why the hell we couldn't get rid of the stumble on my SA until we realized what was happening with the accel pump lever!

Clue

Would that be for all Street Avenger carbs? I have a 770 cfm on my BB

shmoky

I have the same as Clue. So have the same question also.

shmoky

Eddie 70

Good information here. I fattened my primaries up 2 and it helped some. Getting the timing just right has helped the most for me. I guess I need to see if I can adjust on the pump lever a touch too.

wiseman79

Bless you sir! I swapped from an edelbrock to avenger and have been monkeying with pump cams because I noticed what you mentioned about the pump cam not activating as you break idle, and resulted in a stumble. I've gotten used to stabbing the gas a little to get past the stumble point. You're the man. My jetting seems to be close however but may richen it up and see if performance improves.

vetteflsurfer

Lars your the man.

steve dalla

great timing, just broke in new motor (350 Afr195 roller) w/770 carb and had noticed the stumble! Lars is always on point. His articles are like GOLD.

lars

Yes. Especially the 770s - every single one I've seen has had the defective pump lever bend with the lever resting on the spring instead of the cam, and they're all lean jetted.

Clue

Thanks Lars
Do I have to disasemble the carb to change jet's? And what about changing the powervalve, do I have to disasemble carb to change it? I only have 8 inch of vacum so I should maybe change PV to a 5,5 unit if that excist.
Thanks

vetteflsurfer

To make sure I understand, I just looked it up and the 770's come jetted from the factory with a 72 jet on the primaries and a 75 on the secondaries, so your saying put the 75 jets on the primaries and put 83 jets on the secondaries so to have 8 jetting sizes larger on the primaries compared to the secondaries? Thanks.

Edit: Sorry I meant to say have 8 jetting sizes larger than on the primaries.

lars

Depends on what you mean by "disassemble the carb".... You don't have to take the entire carb apart - you just pull the float bowls and metering block - the jets and PV are in the metering block.

Yes, they make 5.5 PVs, and that may be a good choice given your 8" of vacuum.

Yes, put the 75 secondary jets in the primary side, and install a pair of 83s in the secondary. This makes the secondary side 8 sizes larger than the primary - not the other way around as you stated. I've also used 81s in the secondary side with good luck - you can try that if you want to run a touch leaner at WOT.

dgruenke

Thanks for the tip Lars. I have a 770 that I am planning on using for my build.

I am new at the jet changing. Is the jet size clearly marked on the jet so that you can tell if someone has changed them out in the past?

lars

Yes. It's stamped into the side of the jets.
Lars

vetteflsurfer

Sorry, I meant to say 8 sizes larger on the secondary side, just a little scatter brained today I guess. Thanks.

shmoky

Okay... If I need to get larger jets... where do I get them? I tried looking on the Holly site but couldn't find them. (I may just not be looking at the right place so direct me if you can)

Also can't find a dealer in Canada. Is there a refeence # I can use for a different brand maybe? (out of a skidoo??? )

shmoky

vetteguy75

Try Summit Racing ( www.summitracing.com ) or JEGS ( www.jegs.com ) . Just type Holley jets in the "search" section....That's where I got mine...

fugawi

ALL HAIL LARS!!!!

lars

Sorry, but you cannot use jets out of a Skidoo or a Chaparral (if you remember those...). Jets from Strombergs and 2GCs also will not work. Finally, you cannot use oriface plates out of swamp coolers or restrictors from Matco air blowguns. Holley jets are available under Holley part number 122-XX, where "XX" is the jet size. From Summit, the part number is HLY-122-XX. Summit ships internationally, or you can have it drop shipped to me, and I will forward the shipment to you as a "gift" for the customs people. Contact me for further info.

Lars

Matt Gruber

1st try the pump cam lever.
larger jets waste gas. if it is too lean it will surge at cruise. ask yourself, does it surge?