Popping sound at idle ... help
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Popping sound at idle ... help

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    Senior Member Franger's Avatar
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    Default Popping sound at idle ... help

    Hate posting this cheesy video again but I really need help. In the video right when the red stripe (at the bottom of the video) gets to the line between the gear looking thing (quality icon) and the clock looking thing (watch later icon) until the end you can hear what I'm trying to fix, a slight popping sound. I've set the valves to cam specs twice and checked three different times after running, each time all is good.

    My thoughts are carb adjustments but I'm just not sure what carb adjustment (if any) would cause that annoying popping.

    The accelerator pumps levers/arms have no gap/clearance. I have always thought they were supposed to have .015" clearance at WTO throttle but they are tight to the diaphragm at idle position.

    Would a vacuum leak cause popping at idle?

    I have Autolite 24 plugs in the motor, would a hotter plug be better? Would NGK 8 be a better choice ?

    Would appreciate thoughts and info, Thanks guys

    Last edited by Franger; 04-09-2012 at 11:19 PM.

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    Senior Member rocket98's Avatar
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    I really couldn't hear anything. Could you have a lasch cap come off? I will let the more informed comment.
    They older we get the faster we were

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    Cantard 71hallett's Avatar
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    You have a float level to high? Almost sounds like fuel drops. Bad/leaking power valve?
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    S&S
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    Acc pumps should be tight at idle, they should respond to the slightest movement of the throttle. The way to check them, is to manually hold butterflies wide open (in the throat of the carb) first, not with throttle linkage. Then check that there is clearance of .015 at pump arms. Your just checking to make sure they aren't hitting bottom and binding up at WOT.

    As far as the slight popping, I had a single carb TR that used to sound like that at idle. I always thought the same thing, that it had to be an idle circuit/air bleed adjustment. Mine ran good so I never paid much attention to it. I'd say run it, unless it's missing when you get on the gas. Most people won't even notice it. If they do, they need to get their own toy to tune on.
    Last edited by S&S; 04-10-2012 at 07:44 AM.

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    Senior Member Franger's Avatar
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    Quote Originally Posted by 71hallett View Post
    You have a float level to high? Almost sounds like fuel drops. Bad/leaking power valve?
    Have checked floats 4 or 5 times to make sure they're good, each time they were.

    Forgot to include.... carbs are Holley750cfm (6109's) ... bought them from a guy who races. He had them worked on by a popular carb guy to get rid of the starting line stumble.

    Question..... could the carb adjustments made to get rid of the stumble coming off the line be too lean a setting causing the popping? It does it every time when I've run the motor, just like in the video, after the motor is rev'd a few times and left to idle ... the popping happens. It runs fine at rpm's of 1,000 and up ......

    What I gotta do offer to send fresh ALASKA Salmon or Halibut to whoever solves this? Done ... C'mon

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    Canoe Jockey Michael Thomas's Avatar
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    just send me the fish....and I'll keep my mouth shut! Do your 6109's have power valves....I use those carbs and they have no power valve provisions. The metering plates arent drilled for them
    "If you can't dazzle them with brilliance...Baffle them with bullshit"

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    Senior Member Franger's Avatar
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    Quote Originally Posted by Michael Thomas View Post
    just send me the fish....and I'll keep my mouth shut! Do your 6109's have power valves....I use those carbs and they have no power valve provisions. The metering plates arent drilled for them
    No power valves

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    Canoe Jockey Michael Thomas's Avatar
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    Just wondering, how long is your boating season...Here in the northern great lakes region we run them june - sept..the season is kinda short. but gives us time to fix them for the next year.
    "If you can't dazzle them with brilliance...Baffle them with bullshit"

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    Canoe Jockey Michael Thomas's Avatar
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    what do the plugs look like....are your fuels "winter blend" there?
    "If you can't dazzle them with brilliance...Baffle them with bullshit"

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    Senior Member Franger's Avatar
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    Quote Originally Posted by Michael Thomas View Post
    what do the plugs look like....are your fuels "winter blend" there?
    Gonna check plugs later today, running Sunoco 110

    Ice is gone by mid May and we still have temps good enough to run into usually mid Oct

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    Senior Member Hullshot's Avatar
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    Quote Originally Posted by Franger View Post
    Gonna check plugs later today, running Sunoco 110

    Ice is gone by mid May and we still have temps good enough to run into usually mid Oct
    Take the scoop off and let engine idle and make it do its popping thing and look down at the venturi's and see if there are fuel droplets coming off of them, any of them, and then see if it corrisponds to the noise or popping you hear. Does that carb have adjustible air bleeds?

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    The "popping" you're hearing is unburnt fuel firing in the headers. After a "rev up", when you slam the butterflies shut you're leaving excessive fuel in the intake and depriving it of air... There are many sq inches of horizontal surfaces in a T/R to trap liquid fuel, and after whacking the throttle you've filled the T/R with hopefully vaporized fuel that goes back to liquid when you take away the air flow. That liquid fuel is drawn into the cylinders, along with your idle A/F mixture. Liquid fuel is hard to fire, but will "pop" off the second it hits the hot header tube... From the looks of the surrounding area with snow on the ground, you're also dealing with a cold intake, another contributing factor to the fuel returning to the liquid state.... Nothing to really worry about, and on a hot day at the lake/river you may not even notice it....
    Ray
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    Senior Member Franger's Avatar
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    Don, Good idea, I'll check next time I fire it up

    Ray, Wadda ya talking about "cold intake"? ... heck it was 41 degrees that day ... J/K great info thanks a bunch, makes perfect sense

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    Senior Member bp298's Avatar
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    Quote Originally Posted by Franger View Post
    Question..... could the carb adjustments made to get rid of the stumble coming off the line be too lean a setting causing the popping? It does it every time when I've run the motor, just like in the video, after the motor is rev'd a few times and left to idle ... the popping happens. It runs fine at rpm's of 1,000 and up ......
    generally, or frequently, or usually.... a stumble off the line is caused by a leaning condition. to address that, the transition circuit has to be fattened up. or people will install larger squirters. i.e., nobody would intentionally lean the thing out to address a stumble. if the squirters are oversized in an effort to correct the stumble, that would only add to what moneypit was saying. no biggy. just run the thing...

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