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Thread: Tuning questions on a Street Avenger.

  1. #1

    Default Tuning questions on a Street Avenger.

    Good evening guys. I am currently going through a 770 Street Avenger (0-80770) on top of a Pontiac 400. I've been screwing around with the tuning for a while now and I have it pretty well set up with a few minor issues listed below. Any input on how to address them further than what I have done is appreciated.

    1. For starters, the idle. It took forever to get a reasonable idle on the AFR gauge as I was running the idle mixture screws something like 4 turns out just to have it run. And it did make a difference, but it would idle around 17 to 18:1 on my AFR gauge. I ended up using small bailing wire to restrict the idle air bleeds temporarily which allowed it to idle at a comfortable 14.8:1 warm in gear and around 750 RPM. No amount of adjusting the primary and secondary throttle blades would get it any richer but that worked. it was actually a tip from a friend to try. I know the air bleeds can't be changed on a Street Avenger so a more permanent solution or suggestion is greatly appreciated.

    2. Cruising AFR is pig rich. again been told this is an air bleed issue. I'm talking like 11:1 running at 55 MPH. It seems to be un changeable via the primary jets which is fair. They only contribute a small amount it would seem from my reading. I'm also wondering if I'm in the power valve though. Car only makes like 11 inHg of vacuum in gear so I could see the stock 6.5 power valve also being the issue.

    3. It has an off idle stumble on light throttle. it spikes lean in the 18 range. Supplementing it with the accelerator pump in park it goes away. It has the stock red cam on it still. I'm thinking an accelerator pump cam that comes in sooner would be the fix for that. when you smack it hard it is alright though so I think the pump shot size is close enough it just needs to come in sooner. it also does this at cruise if you give it a little.

    4. I rejetted the mains down to a 69 and left the secondaries alone and that brought my WOT AFR to around 12.4:1. Rich but safe for now. So the jetting itself is pretty close now I feel. I think maybe a size or two out of the secondary would have it spot on.

    Thanks for any help. I appreciate the input. I've only really tuned EFI so while I understand and have run carbs on stock vehicles, modified is a whole new animal to me.

  2. #2


    I'd look at the idle fuel restrictors, sounds like you don't have enough idle fuel, which you compensate for by running AFR screws four turns out. That can also cause the hesitation. May also check your transfer slot adjustment. I'd also pull the power valve and see if it's good, if it's bad, it could be the cause of the rich cruise. Get a vacuum gauge and drive the car, I like to set the power valve size by what number I get on a decent acceleration, and drop go two sizes below that vacuum reading. You want the valve to kick in extra fuel under harder acceleration..

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