Unstable Idle

Discussion in 'Troubleshooting & Diagnosis' started by PBZ28, Jul 31, 2020.

  1. 80sz

    80sz Veteran Member

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    Vac advance isn’t absolutely needed. I don’t run it. 36 total in by 3000
     
  2. rocket dawg

    rocket dawg Veteran Member

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    The "avenger series" carbs in my opinion are "fussy" . Buddy bought the off road avenger for his SBC 350 powered Jeep. He absolutely hated it. It was a 670. He ended up with my 600 Holley off my 400. The avenger made his jeep a slug, no power, throttle response was non existent. Tuning was a nightmare. He worked on this carb for months and finally gave up. This was a few years back when these carbs were kinda new. The 600 made the Jeep fly, just bolt it on and go. In his opinion it was a huge waste of money and time. They have to a better carb now than when first introduced. He coudnt give it away. We both now run Sniper EFI . Hope ya get it figured out. There is a Holley forum that ya might want to join and see what they suggest.
     
  3. PBZ28

    PBZ28 Veteran Member

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    Update: After adjusting the carb, air idle screws and curb idle, it has been running pretty good without vacuum advance. Well today I thought I would hook back up ported vacuum and see what affect it would have. My logic was if I didn’t have the transfer slots to exposed it should keep the idle in drive the same. It didn’t change at all after a good warm up road test. Trying the full manifold vacuum again it was back to the same old surging at stops.
    A friend of mine has a Holley 750 model 0-80508S on his Nova and has suggested we try it on my engine. It is performing very well on his engine. What a nice friend! We are going to try it out over the weekend. Thanks to everyone on this forum for your help! Biker, we will also get a long hose to road test with a vacuum gauge in the car. Good idea! More to come as this gets sorted out. Thanks again everyone!!!
     
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  4. PBZ28

    PBZ28 Veteran Member

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    E46E00E4-8EE2-423C-B69D-B4CEA405879A.jpeg Update:
    When my friend with the Nova came by he wanted to check a few things before trying his carb on my Z. Timing was checked with and without vacuum. Ok there with 16 initial and 36 at 3100. With full vacuum advance had 28 initial and 48 at 3100. Next a vacuum gauge was connected to check the idle/air settings on the carb. We tweaked that a smidge but he didn’t like how the needle was moving between 12.5 and 13.5 and sometimes a little more variance than that. At that point he pulls out a propane cylinder connected to a rubber hose. Moving around the carb and manifold nothing until the spot at the number two intake. SOB Leak! Pic attached. I swear I saw gasket material there not long ago!
     
  5. biker

    biker Veteran Member

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    Well that is good news. Bad that you have work ahead, but good that you have a culprit.
     
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  6. PBZ28

    PBZ28 Veteran Member

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    Thanks Biker! Now the fun begins reset timing and carb just in time for winter!
     
  7. G72Zed

    G72Zed Veteran Member

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    Good to hear you found the issue. I would make sure the head and intake face are true and are at the correct angles for proper intake gasket crush.
     
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  8. PBZ28

    PBZ28 Veteran Member

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    Will do. I seem to remember an old Hot Rod article talking about having the right taper to get a good squish on the bottom of the gasket to avoid it sucking oil.
    I’m going to take my time to make sure it will be ready to rock and roll in the spring. Can’t thank you guys enough!!!
     
  9. PBZ28

    PBZ28 Veteran Member

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    A697E600-6531-467E-AEF6-E275F9AFCEED.jpeg Update Again!
    That huge intake leak was the root cause of my surging idle at stops. Whew what a relief! Since I was pulling the manifold anyway I thought it was the time for a new one. I do not race. It’s just a cruiser with some occasional quarter mile fun runs on a deserted black top road out in the boondocks. The old intake was very very close for hood clearance even with a inch and a half air cleaner drop base and not much room at all left above the carb ( SS 750 ) air horns, maybe one quarter of an inch. So out with a very high performing Performer RPM Air Gap and in with a low profile Weiand Street Warrior. Still happy with acceleration and have a nice lopey 850 rpm idle in park and a good lopey 750 rpm idle in drive.
    I do have one oddity. The same pcv valve is now rattling on idle in park. It’s a Napa valve #2057 embossed on the valve body and supposed to be for a 1969 302 Z28. Is it because the divider in the air gap was cut down and the divider in the street warrior is not? Thoughts? Engine is running very good though. I’m thinking maybe try the fixed orifice one with no insides or maybe the one Damon recommends a 1991 Camaro 3.1L V6 pcv??????? THANKS!!!!!!!!!
     
  10. Coadster32

    Coadster32 Veteran Member Lifetime Gold Member

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