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Unread 05-02-2013   #1 (permalink)
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Default Help - Carb Trouble - Can't Lower Idle RPM

Ok, I'm perplexed and out of ideas. I can't get the curb idle below 1200rpm.

I have a 4150-style quick fuel carb, 680 vacuum secondary HR-680-VS. I recently switched to a lokar throttle cable and pedal because my old set-up wasn't getting a full WOT. That is the only change I made. Here's what have....

-302 stock bottom end with trickflow twisted wedge heads, trickflow stage 2 cam, dual plane intake.
-primary jets 70, secondary jets 74, IAB 70/70, high speed bleed 28/28, primary nozzle 31, power valve 6.5, needle &seat 100

I have tried the following:
1) throttle linkage is at absolute zero, curb idle screw backed out and cable linkage has some slack
2) choke is not stuck on high idle
3) my secondary "stop screw" (little set screw that can adjust secondary opening) has not changed since before throttle linkage change.
4) I confirmed that my secondaries are not opening as the lever is not coming off if the stop screw
5) while my idle mix shouldn't have changed, I reset it to 14.7 afr (I have meter)
6) by the way, that my idle screws are only out 3/4 turn from bottom. May open IAB later, but trying not to change too many things.
7) checked for vacuum leaks with carb cleaner while running, disconnected and plugged brake power boost, no other accessories.
8) I tried moving idle mix screws all the way in (to see if power valve is blown) but it does stall as soon as I get 1/2 turn out

What am I missing? This gremlin is driving me nuts! Any one that can help I'd appreciate it.






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Unread 05-02-2013   #2 (permalink)
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Default

Oh...one more thing, even though I didn't touch the timing, I took some timing out and it did reduce the rpm, but only by 100-200 rpm. I'd rather keep my timing in as it gets me 34 deg in by 2500. I run an MSD 6AL.


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Unread 05-04-2013   #3 (permalink)
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Ok...I found the gremlin. I had two vacuum leaks. I re-checked my entire list from the beginning, this time pulling my vacuum port plugs off...and the one in the back had a big hole in it. I also pulled my PCV and the grommet to the valve cover and it had a slight leak. Once I replaced / fixed those two, the idle came back down.







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