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650 Brawler, high idle unless idle screw completely off.

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  • 650 Brawler, high idle unless idle screw completely off.

    Guys, pulling my hair out here. New 650 Brawler, mechanical. I'm trying to work out gremlins in this thing.
    Engine: 302, Trick flow heads, comp cam Duration: 274°/282° Hydraulic Roller, Weiand Stealth dual plan intake.
    Timing: 18° initial, 38° all in.
    Engine builder had the carb set with 72 main jets in the rear and 67 in the primary. Engine runs great when nice & warm. Had the idle at 700. Idle mixture screws adds at about one turn out. Plugs are off white slight tan.

    I was trying to figure out a choke issue which lead me down a rabbit hole. Pulled the carb and realized the curb idle screw wasn’t even in contact with the leaver. So I researched and determined the primaries and secondaries were off. I set the primaries to show .020" of the transfer slot. I then backed off the secondaries screw until it was just resting and turned it in 1/4 turn which opened the secondaries slightly.

    Installed everything and the engine idles at 1,800 RPM. I’m thinking vacuum leak right? Well, I first used a hose and put one end to my ear and went around everything I could with the other. No hissing sounds that I could find. I then sprayed carb cleaner along intake seam and anywhere I could. No change in RPM. I then squirted some right into the car, and RPM dropped some. I then pulled the PCV and kept it connected to the carb and put my finger on it. Good vacuum pull. I then put the PCV back into the head cover, pulled the vent cover on the other side and put a piece of cardboard over to seal. No change in RPM. When I pulled the cardboard off there was a definite vacuum.

    I’m stumped. Engine idles at 1700 RPM unless I drop the curb idle screw right down until it’s not touching. Tonight I pulled the carb again. Reset both primaries and secondaries. I then installed the secondary idle screw from the top. This way, I can at least adjust the secondaries without having to pull the carb. Just need to shut the engine off first. I’m too tired to install. Will try again tomorrow. Am I missing something? Everything points to a vacuum leak, but I can’t seem to find it.
    Last edited by Dans68; 05-18-2021, 02:20 PM.

  • #2
    Does this have an automatic choke?
    Are you sure the fast idle cam is not in contact at warm idle?
    What RPM drop did blocking the PCV valve cause? Gary
    Regards, Gary


    • #3
      Absolutely positive the fast idle cam is off. If I pull the hose from the carb, the RPM drops and the car stalls. If I pull the PCV still connected to the line to the back of the carb and plug it, the RPM barely change, or just move up ever so slightly. I should have paid more attention to that test. Sorry.


      • #4
        I'd close both throttle shafts, and then open them 1/4 turn.
        Start the engine, trim the primary side if the engine is way too slow, to say 600, them trim the hot idle with the secondary.
        Some carbs have late transfer slots, so the ".020, or square" rule doesn't always apply. Gary
        Regards, Gary


        • #5
          Put the carb on last night with the secondaries completely closed. Primaries open to the Holley recommended setting of .020" open transfer slot. Once good and warm, the engine was idling at 1400 RPM. It took a full turn of the curb idle screw to get it down to 800 RPM. I suspect there's maybe .050" of the transfer slot remaining. So either I have a ghost of a vacuum leak, or something is up with the carb itself. Anything else I can check on the carb?


          • #6
            Well, the good news, no vacuum leak. I used a smoke machine and it stayed pressurized for five minutes at least and nothing. No leaks anywhere.
            Bad news, still idling high. I’m going reset the idle mixture screws to 1-1/4 turns out and adjust all over again using a vacuum gauge.
            Also wondering if my timing is too advanced? 18° initial. 38° all in. Advance vacuum is coming off timed port from carb.
            It doesn’t ping at anytime and starting has never been an issue, cold or hot. Maybe I have a blocked fuel port somewhere in the carb?


            • #7
              Originally posted by Dans68 View Post
              Also wondering if my timing is too advanced? 18° initial. 38° all in.
              18° idle timing is fine. 38° is fine if that's what makes the most power.
              May God's grace bless you in the Lord Jesus Christ.
              '92 Ford Mustang GT: 385"/6.3L SBF, Dart SHP 8.2 block, forged steel crankshaft & H-beam rods, forged pistons, Trick Flow Twisted Wedge 11R 205 CNC Comp Ported heads, 12:1 compression ratio, 232°-244° duration/.623" lift/114° LSA camshaft, TFS R-Series FTI Comp Ported intake, BBK 80mm throttle body, Holley Dominator MPFI & DIS, Holley 36-1 crank trigger, MSD 1x cam sync, PA PMGR starter, PA 200A 3G alternator, Optima 34/78 Red battery, 100HP progressive dry direct-port NOS, R134a A/C, Spal Dual 12" HP 3168 CFM fans, Frostbite 3-core aluminum radiator, Pypes dual 2.5" exhaust, off-road X-pipe, shorty headers, Earl's -6AN fuel system plumbing, Walbro 255 LPH in-tank pump & Pro-M -6AN hanger, S&W subframe connectors, BMR upper & lower torque box reinforcements, LenTech Strip Terminator wide-ratio Ford AOD, 10" 3000 RPM C6 billet converter, B&M Hammer shifter, Stifflers transmission crossmember & driveshaft safety loop, FPP aluminum driveshaft, FPP 3.31 gears, Cobra Trac-Lok differential, Moser 31 spline axles, '04 Cobra 4-disc brakes, '93 Cobra booster & M/C, 5-lug Bullitt wheels & 245/45R17 M/T Street Comp tires.


              • #8
                Did you figure this out yet?