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Thread: Rich idle out of gear, perfect in gear? Do I need a higher stall converter?

  1. #1

    Default Rich idle out of gear, perfect in gear? Do I need a higher stall converter?

    I'm working on a K5 Blazer has 375 HP 420 ft/lb 383 with Performer RPM intake, 9.5:1, 2¼" dual exhaust. It has a Summit HEI distributor that is been recurved. Idles with 14° in or out of gear, gets 32°-34° by 3000, as I don't have a tape on it just the digital advance like to check it. Carburetor is a Quick Fuel Off Road 680 vacuum secondary.

    Here's the problem I'm having with it. I can get it to idle lean out of gear without it being to lean in gear. If I get it to idle at 13-13.5 AFR (13-13.5 is where it is at highest vacuum) out of gear, when I put it in gear it drops right down to 14.8-15.5 and tries to stall out. When it's right in gear at 13-13.5 in gear, it's 10.8-11 out of gear or anytime it is on compression like cruising down a hill. Only gets like 10-11 MPG. I thought it might be timing, but if I hook the vacuum advance can to manifold vacuum to give it an extra 10° at idle, it wants to idle at 1250 out of gear to get the 600-650 in gear. Idle timing stays the same at 14° in or out of gear.

    I thought about changing the IFR air bleeds, but the fuel curve is almost perfect. With secondaries wired shut on just the primaries, it cruises at 13.4-13.8 AFR and drops to 12.6 on the power valve at WOT. Then with the secondaries hooked up, it runs starts at 12.8 AFR when they start to open and walks right down to 12.5-12.6 at WOT though 5500.

    Is there something else I'm missing or do we just need a high stall converter to take load off of it? The converter in it, is the stock converter that was behind the worn out 350 that was in it before. That's why I'm thinking converter, and if so, how high of a stall should I go?

  2. #2


    By the sound of it, it's not that radical of a engine, so it should behave OK with good street manners. Something you said that's troubling is that it drops 600 RPM to just put it in gear. Something is going on there I would be trying to find. Unless you have some 2.50 rear end gear, there's something wrong. Vacuum leak possibly. Fuel pressure low. Fuel level in bowl to low, something is off.

    So what's going on here is the huge change in RPM to go in and out of gear. If you hook up your vacuum gauge in and out of gear you going to see a pretty good change of vacuum. The vacuum signal the carb is receiving is changing (going lower) as you put it in drive, and therefor not pulling as much fuel. This is what's causing your lean situation at idle in & out of gear. Your adjusting the carb while in park, and then putting it in drive and seeing the problem.
    Primarily you gotta figure out what the huge drop in RPM is caused by. That's the main problem. Once you can get that down to more of 200-300 RPM drop then you can zero in on your idle and transfer circuits.

    When you watch video or read about adjusting the idle circuit. It's advised to do it with car in drive and car blocked with emergency brake on. Here are some things you can do to try and help the situation with out digging into the carburetor to much.
    1. Raise the fuel level in primary bowl to about 3/4 up the glass. Allows fuel to flow a little easier with a same amount of vacuum. (Not so much it flows out of booster.)
    2. Raise the fuel pressure up into the 7-8 psi range if not already there.
    3. Restrict the Idle Air Bleeds a little and that should get fuel flowing sooner as well (this either requires buying an air bleed kit or drilling out your own blanks).
    Just depends on how far you want to go.
    4. You could try to open up your IFRs .001"-.002" but this will require delicate drilling and precise drill bits.
    Last edited by 69cam; 01-11-2018 at 10:53 AM.

  3. #3


    I didn't even think of it, might have to check the power brake booster. Make sure it's not leaking with the brakes applied or leaking worse with the brakes applied, as we had it in gear with the with a friend holding the brakes not blocked with the parking brake on. It didn't seem to mess up with just the brakes applied before putting it in gear. Will have to check it though.

    I tried different fuel bowl setting with no change. I wanted to raise the IFR up a little to help it but idle screws are at 3/4 of a turn I figured I would run out of adjustment or make them to sensitive if I gave them more fuel. I guess I will try going a little smaller with the idle bleeds and see if that helps it out.

    You're right on the vacuum dropping. It does drop about 5 inches or so, but the converter is pulling pretty good on it. Thanks for the advice, guess we'll have to do a little experimenting this weekend.

  4. #4


    If you're only 3/4 turn out on idle mixture screws, then don't open the IFRs. It will make them adjust to under 3/4 of turn and get sensitive quickly.

    Instead of buying air bleeds to figure out how far you need to adjust, you can restrict your current air bleeds to simulate a smaller IAB. Couple ways of restricting IABs, but let be SUPER CAREFUL ABOUT NOT LETTING WHATEVER YOU PUT IN THERE GET INGESTED IN TO THE ENGINE.

    That being said, you can use different gauges of electrical wire to restrict the idle air bleed. Strip a 1 inch section of 14, 16, 18 gauge wire, and use 1 strip of wire from each one as a test. I would unscrew the air bleed a thread or two, wrap the copper wire around it, tighten it, and then poke the other end in the air bleed. These will be certain it doesn't let go into the engine and restrict the air bleed. EVERYTIME YOU MESS WITH THE IABs you will need to readjust the idle mixture screw for best vacuum. it will change.

    I had a guy once tell me, SWING FOR THE FENCE on changing bleeds. Basically meaning make a pretty big change initially to get a baseline of exactly what it's gonna do. Don't be scared to start with the 14 gauge wire. Start it, and if it's super lean back out the idle mixture screws. If those can't correct it, then go smaller wire size and try again. Once you find a restriction that's good you can determine what size of air bleed you need from there. Restricting the air bleed will just make the idle circuit flow sooner or later. It does not change the amount of fuel allowed to flow. That's done with idle mixture screws.
    Last edited by 69cam; 01-11-2018 at 01:34 PM.

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