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Thread: Street Avenger 770 lean transfer, cruising RPM.

  1. #1
    dteeter Guest

    Default Street Avenger 770 lean transfer, cruising RPM.

    Ford 331 stroker, Edelbrock Air-Gap, RPM Performer 195 heads, 10.5 compression, .560" lift, 9 in of vacuum with a 3.5 PV, 14° initial, 35° total timing, no vacuum advance, 5 speed, Fox body, not sure on the gear ratio. AEM AFR gauge, and last but not least my worst nightmare, a 770 street avenger vacuum secondary. I know its to big of carb for the cubes, and I probably should have a 650 mechanical, but, I ended up with this one and have it dialed in except for the one critical spot where the car wants to cruise down the road.

    Symptom: Cruising speed lean condition, like no fuel lean. And no, it's not the accelerator pump or nozzle size issue. The transfer port is not delivering enough fuel for cruising speed.

    I can tune the secondary once I get the primary circuit figured out. I have the primary set right with the transfer port showing as a square beneath the throttle plates, idle speed is set with adjusting the secondary open to provide more air. I can dial in the idle circuit with the with the idle mixture screws perfectly. Accelerator pump is standard size with a pink cam, 32 nozzle, works great. The problem lies with the transfer circuit, just before the main boosters start. I'm running 69 jets in the primary, which is right where it needs to be in the mid range, 13.5 to 14 AFR. However, in 5th gear running on the main circuit I would be doing 100 MPH or so down the road. I've read hours of posts about the street avenger carbs have metering blocks that are lean and this makes sense. I've tried every trick in the book and then some to try to tune around this lean condition. I either need to drill out the metering block, tap in some air bleeds, or get a new metering block from Quick Fuel, which is the fix apparently? I'm posting this on here hoping that someone can help me determine which metering block I need or how I can drill out my existing one? I need to get more fuel to the transfer slot. Help will be greatly appreciated. Thanks.

  2. #2
    Join Date
    Nov 2014
    Ont. Canada


    You have two choices. Open up the idle restrictor, or make the idle air bleeds smaller. As a test, you can get a thin piece of wire and loop it around your squirter, then put the ends in the idle air bleeds.This will be the same as making the air bleed smaller. I've drilled out many air bleeds and used brass set screws drilled out to what I needed.

  3. #3
    dteeter Guest


    I have a regular 750 double pumper that I took off the primary metering block to compare to this SA 770. I noticed that the transfer/idle circuit inlet of the 770 had a brass restrictor and the 750 didn't. I decided drill out the restrictor enough to open it up. I started drilling, pulled out the drill bit and noticed that the size of the hole went from good sized to a pin hole deeper in, that was the problem with the transfer slot lean issue. After the drill out, the AFR went to 10.5 while cruising down the road where it used to be at 17 and the lean spot just before the main circuit would start to run was gone. I put in a good sized piece of wire into the drilled out hole. That took it from 10.5 to 12, so I added a couple of smaller wires and it was perfect at 13.5 to 14 cruising. However, the lean spot came back but at a higher rpm than before and a shorter duration just before the primary circuit takes over. I need some more tips to keep tweaking this thing. I didn't try leaning out the air bleed for the transfer slot as I have a lean condition? At this point, I don't know if its best to buy a new Quick Fuel's adjustable metering block, If so, which one? Or do I spend more money on a smaller carb, like a 650 or 670 mechanical rather than the vacuum secondary 770? If so, which one? The other issue is that now that we have it almost driveable on the primary, we started messing with the secondary. One a decent pull the secondary only opened about a 1/4 and was about an 11/11.5 on the AFR. Since the mid range circuit is running perfect for cruising, didn't want to mess with it, so I put a good sized wire in the PV ports, probably shut them down by 85%. This helped, brought the AFR up in the 12's where it should be at WOT, but the secondary is still opening about 1/4. The secondary spring is a yellow one, not sure if its the short or long one. Wondering if this 331 has enough to run this 770, if I'm expecting the secondary to fully open when I don't have enough cubes to do it? We don't have the tach working yet, but the rev limiter is set at 6800 and we have not hit that yet.

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