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Thread: 670 Street Avenger Problem

  1. #1

    Default 670 Street Avenger Problem

    I've had a couple of goes at trying to get this carburetor sorted. I'm at a loss as what the problem is. I have a pretty standard 400 SBC that's .030" over, it's nothing fancy with a 700R4 behind it. I've been running a 750 DP on it that I've been borrowing and I purchased the 670 because it was recommended. The engine was running nice with the 750 and then I put the Avenger on. It has trouble starting & it won't idle in gear. I've had to turn the idle mixture screws out almost 3 turns just to get it to idle in gear, but it's a rough idle with a bad miss. Pull it into gear and try to drive it away, and it still has a horrid miss. But mash the pedal and it gets past the miss & runs great. When cruising, it has the same miss at low rpm, but hit the throttle and it takes off again. I've tried tuning it, tuning with a vacuum gauge like I usually do, but it has me perplexed. I've removed the 670 & put the 750 back on, and it run fine. Any help would be great.

  2. #2

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    I've found the idle feed restrictors in my Holley 670 were way too lean.

  3. #3

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    Good to know. I've been chasing a possible vacuum leak, and it's driving me crazy. I've even changed the brake booster thinking it was the problem. So how did you fix it, if you don't mind me asking?

  4. #4
    Join Date
    Aug 2016
    Location
    Sacramento, CA
    Posts
    10

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    To find your leak, unplug all vacuum hoses paying attention where they go. Use blue tape and label them or take a lot of pictures. Then buy an assortment of black rubber plugs in a box at AutoZone or your local parts house and plug all the nipples on your carb, the big one in the back for the brake booster, the other big one for the PCV valve, even the smaller ported ones like for the distributor vacuum advance. You don't need it for testing at idle, plug them all off and see if you still have a leak. If so, remove the carb and check the base plate, they sometime crack around where the big nipples come in like in the back where the brake booster hose goes on. Also they plates can warp and not be perfectly flat, check them with a metal ruler/straight edge, check your intake manifold as well. If the carb is off buy a new bottom gasket (don't reuse your old one especially since you are hunting down a vacuum leak). Take your time and you'll find it, it can definitely be frustrating. In my case, spraying some carb cleaner or WD-40 to find the exhaust leak around the carb has never worked, although I knew I had a leak, just sharing that with you.

    Also, what distributor do you have and what is your initial timing advance set to and what is your total timing set to. And I can not say enough about spark plugs. Check them and then check them again, are they all gapped the same are they gapped right.

    And then there's the spark plug wires. Are they cracked, are they good, what resistance are they. Check each one with a multimeter and see if they are within specs. You will be surprised what a difference proper resistance spark plug wires make when they are healthy & happy. So worth the PIA of going through each one and testing each one at a time.

  5. #5

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    Yeah, I checked every possible place for a leak I could. I used carb cleaner all over it, and nothing changed in its idle. Doesn't matter what I did, I could not find the source of the vacuum leak, but that's just what it's like. If it's not a vacuum leak, I don't know what it is. It's definitely a problem with the carb, because I borrowed some others to try on it, and there was no sign of any leak what so ever. The engine ran great. Put the Avenger back on and it went like crap. So I decided to purchase a fuel injection system instead. I'm not even going to bother playing with the Avenger anymore. I've spent enough money and time trying to find out the problem and can't justify playing with this piece of garbage anymore.

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