Big Cam Bad Idle :( - Team Camaro Tech
Tech 2002 General Tech questions from 2002
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post #1 of 17 (permalink) Old May 19th, 02, 03:56 AM Thread Starter
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I am at the end of my rope..As some of you have been following along with my problem..

I have a SBC 355 10-7-1 comp,Lunati cam [email protected] duration with 511 lift,TH400 with a 2200 stall....Edelbrock 600 carb..Timing advanced at idle 19* with a total of 38 in by approx 3000rpm..With vacuum disconnected ..

The problem is I can't get it to idle..I will set idle around 1000-1200rpm It will idle fine for about one or two minutes then the idle will slowly drop and the car will stall...I am running a edelbrock 600 with blue metering springs(blue springs rated at 3" I am pulling 6-7" at idle..)..But I am still getting some occasional dribble from the primaries at idle and believe that maybe my problem..Do you guys think that the dribbling from the primaries is causing it to load up at idle and stall out...Edelbrock tech tells me the idle needs to come down below 900rpm So I can get back into the idle circuit..(I have the idle screw turned out so much I am basicly out of the idle circuit and opening the primaries)..

Also someone here recommended I drill a some small holes on my throttle plates..They stated that that would help me lower my Idle...How does this work and how do I do it

Thank again

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post #2 of 17 (permalink) Old May 19th, 02, 05:32 AM
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The idea behind drilling small holes in the butterflies is to give you a little more air to get the engine to idle without having to open the throttle blades so far and getting past the idle circuit. Often with a large cam by the time you get the blades open enough (enough airflow) to get it to idle you're past the idle circuit and into the cruise area or main circuit. The fuel dribbling is a very good indicator that you are there. The carb is thinking you're cruising down the road under light load but you're not.

There are a few other solutions before drilling holes if you were running a Holley; do you have access to one? Usually if I'm running that large of a cam I'm looking for the most performance I can get. The Edelbrocks are nice street carbs, but I don't use them on something like you have. The Holley's and Demons usually have the secondary butterfly adjustment plus most have four corner idle circuits. Between those two areas I bet you could get this thing to idle without drilling any holes.

Jody
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post #3 of 17 (permalink) Old May 19th, 02, 05:42 AM
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I had a similar problem on my car as well. I had a holley 850, but it didn't have a four corner idle circuit. Since this was too much carb in the first place, I bought a holley 750 w/ a four corner idle circuit. I was able to solve the problem with the secondary butterfly adjustment screw on the bottom of the carb. This allows the secondary butterflys to be opened just enough to allow more air flow. This, along w/ the four corner idle circuit took care of it. Now I can idle at about 850 rpm and have enough vacuum to work the power brakes.
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post #4 of 17 (permalink) Old May 19th, 02, 08:25 AM
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One thing I'd try is running the vacuum advance hooked directly to a manifold source instead of a ported source. This will give you some vacuum advance at idle which will help you get it to idle without having to advance your base timing too much (which may cause detonation and hard starting).

I have seen a few big cam engines that work well with the small hole drilled in the throttle blades - haven't done it myself though, so I can't help with the details.

Also, If its a hydraulic cam, you might try installing Rhoads lifters or the Crane equivalent. I've used the Crane's before when I was overcammed and they worked well. BigRed-L72 swears by the "big cam / Rhoads lifter setup" so maybe it could work for you too.

Good luck.

ps. Make sure if you run an electric fuel pump that it is regulated down to 6 - 7 psi max. I'm not 100% sure about the Edelbrocks, but the Holley WILL leak by at around 8 psi.

[This message has been edited by Eric68 (edited 05-19-2002).]
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post #5 of 17 (permalink) Old May 19th, 02, 09:22 AM Thread Starter
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Jody,68BB427 and eric68..Thanks for the info..Do you guys think a 750 Demon would work..I hear alot of good things about the demons...I have used holleys in the past with no complaints but was just running the idea through you guys...Would the demon have a 4 corner idle and secondary butterfly adjustmnet..If you guys are set with the holleys I will just order another holley...

Eric 68.. I am running a holley red pump with no regulator..I was told I don't need one with the holley red..That they are self regulated..Is this info correct or should I order a regulator with my new carb...Oh yeah..I am running manifold vacuum for my advance...Thanks again

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post #6 of 17 (permalink) Old May 19th, 02, 09:37 AM
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I am having a few issues at the same time and am waiting for a parts order but when it comes in, I will be playing with the secondary butterfly stop first, then the holes in the primaries if that does not do the trick for mt Holley. The UPS guys are running a bit slower than I would like lately.

-Mark.
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post #7 of 17 (permalink) Old May 19th, 02, 11:41 AM
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I don't know too much about small blocks in regards to appropriate carb size, nor do I know too much about Demon carbs. I know, a big help, huh. Here is a link to the demon site, it looks like they do offer carbs w/ four corner circuits. As far as the secondary butterfly adjustment, I didn't find it. If your considering the demon, I'd call their tech line and run your engine set up and problem by them. I'm sure they can give a recommendation. Hopefully someone else here will be able to offer more info. www.demoncarbs.com/demoncarbs/

Bob

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post #8 of 17 (permalink) Old May 19th, 02, 12:47 PM
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The Speed Demon would probably work fine; they have four-corner idle mixture adjustments and secondary throttle adjustments. They make both 650 cfm and 75o cfm.

Jody
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post #9 of 17 (permalink) Old May 19th, 02, 12:51 PM
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Sorry, double post

[This message has been edited by Camcojb (edited 05-19-2002).]
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post #10 of 17 (permalink) Old May 20th, 02, 09:43 AM
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I don't know if the Holley Reds are internally regulated or not. You could always get a cheapo fuel pressure gauge and watch the pressure - especially at idle and WOT.

If it goes high while idling, I'd say you need a regulator. If it goes low at WOT you'll go lean and could potentially hurt the motor.
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post #11 of 17 (permalink) Old May 20th, 02, 09:58 AM
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Also, the holley HP series 4150's work excellent-- I'm running a similar setup but more cam (260/264 @.050 - .634 lift) using the HP950 with the down leg boosters (which is really a 750 w/the flowed out body)... idles excellent, already has the holes in the throttle blades, 4 corner idle, etc. Noticable power increase from when I had a 650 double pumper on it. One side note- avoide annular discharge on the street-- kind of a 'all or nothing' carb, great for racing, but not street driving.
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post #12 of 17 (permalink) Old May 20th, 02, 11:48 AM Thread Starter
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68six speed..How is your idle with such a big cam and that holley carb...Were you able to get it under 1000rpm at idle...Also that particular holley comes with the hole already drilled in the butterflies is that correct???...Thanks for the info

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post #13 of 17 (permalink) Old May 21st, 02, 02:40 AM
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I have a very similar SBC to yours, except 11.7:1 compression and a .600/.600-244 duration hydraulic roller cam. I have a Gary Williams 750 carb (Flows 830cfm), which is basically what Holley now sells as the 750HP, the Holley HP seried carb will solve your problems, Edelbrocks are more for mild street motors. Many guys I run with have had issues with the Demons...

[This message has been edited by CrossRamZ11 (edited 05-21-2002).]
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post #14 of 17 (permalink) Old Jul 6th, 02, 03:56 AM Thread Starter
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Well went out a brought a new perf edelbrock 750 and problem fixed...car idles as low as 800..But prefers 1000..idles mixture screws work and am now pulling 7-8" of vacuum...Just need to fine tune..When I snap the throttle I am getting some black smoke..I believe I may be a little to rich just off idle...But I will work it out(I hope)
But just want to thank everyone for there help

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post #15 of 17 (permalink) Old Jul 6th, 02, 09:17 AM
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Do you have an automatic choke on your car? If not, you'll have to set the idle mixture rich enough to start and run, but as the motor warms up it will load up with fuel. An automatic choke will compensate by opening the choke plate as the motor warms up - leaning the idle mixture.

-dnult
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