Idle air bleeds.. - Chevelle Tech
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post #1 of 16 (permalink) Old Feb 16th, 17, 10:00 AM Thread Starter
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Ron
 
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Idle air bleeds..

I have been having trouble with my Quick Fuel carb running really rich and fouling the spark plugs. I searched high and low on line for a solution but never found anything that worked and I never found any mention of the idle air bleeds. Yesterday I emailed Quick Fuel about it, they got back to me right away and told me to increase the size of the air bleeds. He said my carb should have "70"s in it (it does) and to go up 3 sizes at a time until it clears up. I ordered them today, I'll let everyone know if it fixes it.
Its been pretty frustrating to say the least, if I let the car idle for more than a minute or two it will foul at least one or two spark plugs.

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post #2 of 16 (permalink) Old Feb 16th, 17, 1:13 PM
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Yes larger air bleed will lean out the idle circuit. How many turns did you have idle mix screws out with the 70 bleeds ??

Plus hopefully you have enough idle timing vacuum and base around 20

Timing slso effects rich idle
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post #3 of 16 (permalink) Old Feb 16th, 17, 9:32 PM Thread Starter
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Re: Idle air bleeds..

Quote:
Originally Posted by CDN SS View Post
Yes larger air bleed will lean out the idle circuit. How many turns did you have idle mix screws out with the 70 bleeds ??

Plus hopefully you have enough idle timing vacuum and base around 20

Timing slso effects rich idle
Bill, timing is 18* initial, 38 total at 2500rpm, not including the vac advance. Idle mix screws were out from 3/4 to 1 1/2 turns, tried it everywhere in between.
Hoping these air bleeds fix it.

70 Chevelle SS396 (496) Straub roller, M21
69 Malibu convertible
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post #4 of 16 (permalink) Old Feb 16th, 17, 9:42 PM
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Bill
 
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Ok good if it that rich with that timing and you had 11/2 turns out and both pri and sec blades not into transition circuit then at least 3 sizes bigger pbly closer to 80,s
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post #5 of 16 (permalink) Old Feb 16th, 17, 10:36 PM
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Re: Idle air bleeds..

racingfuelsystems.myfunforum.org - Index page

Need any carb help this is the place to go. There are some awesome guys there.
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post #6 of 16 (permalink) Old Feb 17th, 17, 3:59 AM
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Re: Idle air bleeds..

Did you post about that here? I don't recall seeing it?

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post #7 of 16 (permalink) Old Feb 17th, 17, 4:42 AM
von
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Re: Idle air bleeds..

Just FWIW in the early 70's I had trouble with the orig 780 cfm Holley on my L78 Nova getting dirt in the idle air bleeds and causing the same symptoms you describe. Your problem could possibly be partially clogged air bleeds instead of too small. I don't know if it applies to your carb but there's the blown power valve issue.

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post #8 of 16 (permalink) Old Feb 17th, 17, 8:02 AM Thread Starter
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Re: Idle air bleeds..

Quote:
Originally Posted by Tom Mobley View Post
Did you post about that here? I don't recall seeing it?
I don't remember if I asked about the carb or not, I know I asked about hotter spark plugs because of fuel fouling issues.

70 Chevelle SS396 (496) Straub roller, M21
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post #9 of 16 (permalink) Old Feb 17th, 17, 1:42 PM
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Mark Whitener
 
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Re: Idle air bleeds..

How about some engine specs. Timing is your friend with cams that have low vacuum at idle/low RPM's. And the QF carbs can be helped with by lowering the idle feed location and putting in transition slot restrictors.
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post #10 of 16 (permalink) Old Feb 17th, 17, 2:43 PM Thread Starter
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Re: Idle air bleeds..

Quote:
Originally Posted by jmarkaudio View Post
How about some engine specs. Timing is your friend with cams that have low vacuum at idle/low RPM's. And the QF carbs can be helped with by lowering the idle feed location and putting in transition slot restrictors.
496, 10.3:1 comp, 049 heads with 2.19/1.88 valves. Clay Smith hyd roller BBC 454 to 470 CID ?Old School? OEM 049/781 heads to a max of 5700 RPM - Clay Smith Cams . timing as above ^^. 4 speed, 3.31 rear. Total street car.
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post #11 of 16 (permalink) Old Feb 17th, 17, 7:40 PM
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Mark Whitener
 
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Re: Idle air bleeds..

Does it have a vacuum advance? Having more timing at idle but pulling enough out under a load will help. Needs to have base timing as high as it will tolerate at full load/low speeds, mechanical curve to add more as RPM increases, vacuum advance for low loads.
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post #12 of 16 (permalink) Old Feb 17th, 17, 8:02 PM Thread Starter
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Re: Idle air bleeds..

Quote:
Originally Posted by jmarkaudio View Post
Does it have a vacuum advance? Having more timing at idle but pulling enough out under a load will help. Needs to have base timing as high as it will tolerate at full load/low speeds, mechanical curve to add more as RPM increases, vacuum advance for low loads.
Yes the vacuum advance is hooked up and working. I have the initial at 18* now but have tried it up to 22, no difference in the way it runs but it detonates pretty badly any higher than 18 when under load.

70 Chevelle SS396 (496) Straub roller, M21
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post #13 of 16 (permalink) Old Feb 18th, 17, 9:28 PM
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Re: Idle air bleeds..

How much timing at idle with the vacuum hooked up? And do you have it hooked to manifold vacuum?
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post #14 of 16 (permalink) Old Feb 19th, 17, 6:22 PM Thread Starter
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Re: Idle air bleeds..

Ok, I got the larger air bleeds in, the carb had 70's in it originally, I went to 76's. After ordering them I thought I probably went too big but I figured they are cheap enough so I would give them a try. So, it runs great and I cant see any downside, the idle doesn't seem near as rich. I let it sit and idle about 20 minutes, no fouled plugs and ran good after sitting there idling. Maybe this fixed it, if not I'll try idle air restricters in the metering blocks. As of now it seems fine.
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70 Chevelle SS396 (496) Straub roller, M21
69 Malibu convertible
95 Z28 Convertible T56 6 speed
TC #54 Gold

69 - Top down
69 Top up
new wheels
70 side
On Gearz
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post #15 of 16 (permalink) Old Feb 19th, 17, 7:19 PM
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Good. I pbly would have gone to 80's and used idle mix screws to rich ip if too lean
Assume you readjusted the idle mix screws ans idle speed screw hopefully you were anle to back off idle speed screw and still maintain your desired idle in gear speed. How far out ate the ifle mix screws
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