Holley carb. adjustment - Team Camaro Tech
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post #1 of 8 (permalink) Old Jan 27th, 02, 03:52 PM Thread Starter
Join Date: Jan 2002
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I have bought a used 650 holley to replace my worn out Q-jet and upon installing it I have found that it seems to run very rich. I have installed a smaller powervalve after having the vac. tested and it did not help. The adjustment screws on the bowls seem to have no effect on the idle.

My setup is a 327 w/350 heads, a large cam, headers and 9:1 compression.
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post #2 of 8 (permalink) Old Jan 27th, 02, 05:12 PM
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Have you got your cam specs.--what is your idle rpm?-how much vac. at idle?
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post #3 of 8 (permalink) Old Jan 27th, 02, 05:18 PM
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Location: Ashby,MN, USA
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throw a rebuild kit in it, and find out what the stock calibration was for it- jetting and what not. you can find this info at www.holley.com , i believe.
in a nutshell, just get it back to stock and start over with it.

1971 Nova(looks like 69 camaro from underneath!)
355sb, vortec heads, HOT cam,T-10 tranny, 3.70 gears 16X8" IROC wheels
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post #4 of 8 (permalink) Old Jan 28th, 02, 12:12 AM
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www.mortec.com has alot of info that might help too.

My '68 Camaro
Doug G.
68 Camaro
406 ci.
[email protected] W/ 2.73POSI.
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post #5 of 8 (permalink) Old Jan 28th, 02, 05:16 AM
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Way too rich. You either have a float that is too high and leaking into the carb, or the jets are too big. Unless the power valve is blown, it will have no effect on idle. When running and idleing, pull off the cleaner and look into the carb. See if you can see fuel dripping into the carb in either the front or rear ports. If so, then that usually means the floats are too high and it is leaking that way. If you don't see nay drips, then consider dropping the jets about 3 sizes and see where that gets you. I have learned thru experience not to trust any other documentation other than your own testing as to what your motor actually needs for jets and such. You can start with stock jetting, but will probably need to modify it to your engine.

Good luck,
Bill C.

Bill C.
Colorado Springs, CO

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71 Chevelle SS
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post #6 of 8 (permalink) Old Jan 29th, 02, 06:34 AM
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I've got the holley bible..
check back with the list numbners

(on the airhorn)
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post #7 of 8 (permalink) Old Jan 29th, 02, 12:01 PM
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The idle mixture screws have no effect because the throttle plate is open too wide, so it's idling from the transfer slot instead of the idle system. Unless your cam is really radical, you should be able to go back to baseline (idle mixture screws out 1-1/2 turns from lightly seated) and get it to idle properly after closing up the throttle plate some by backing off the idle speed screw, then tweak the mixture screws for highest vacuum (all of this assumes you've checked and properly set your float levels). Also check and make sure the idle air bleeds aren't clogged (little inserts with orifices in them just inside the air horn) - if the carb was run without an air cleaner, they could be clogged.

'69 Z28 Fathom Green
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post #8 of 8 (permalink) Old Jan 30th, 02, 01:28 AM
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I am having kind of the same problem with my holley. I had a Holley 650 with a 4.5 power valve and the car ran great. I decided to try a new 750, so I put the 4.5 powervalve in this carb and the car won't even run. I have to have the idle turned way up so it will idle. About an 1/8 inch of the slot showing underneath the butterflys and the idle mixture screws has absolutley no affect when i turn them in or out. i know the car should want to die when they are turned all the way in. My floats are fine. The only thing i can think of , but I am not sure, is the jetting is way to high 71 in front, 80 out back. It wants to pop through the carb and backfire like a lean condition though. I put all new gaskets and new 4.5 powervalve. I need help. Thanks, Erik Beckett

68 Camaro RS, Built 355, 274 Comp Cam, Sportsman II Heads 200 c.c. 2.02. Ported to Performer RPM Manifold and 1.75" Headers, 1.5 Roller Rockers, 650 Holley, Steel Crank, 4.11 Gears but no posi yet! TH350 tranny w/ shift kit.
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