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Old 07-19-2007, 03:19 PM
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Flat spot

I have a Edelbrock 1406 carburetor and it has a flat spot. I am used to Holleys and have no problem figuring them out.
When you first give it the gas it has a flat spot(hesitation). I have increased the base timing, rebuilt the carburetor, changed the vacuum advance from full vacuum to ported vacvuum and back again, adjusted the accelerator pump linkage both ways with no change. When you give it the gas I get a good shot from the squirters, above idle when you nail the gas the engine accelerates clean with no hesitation.
Does anyone have any ideas? I'm thinking that the distributor advance might have something to do with my problem. It is a points distributor converted over to electronic with a Crane conversion The Engine is a .030 over 283 SBC, Edelbrock performer RPM intake manifold. fairly wild camshaft(don't remember the specs), 9 1/2 compression no exotic heads and Lake style headers.
I have checked out the Edelbrock manual on the carburetor and it didn't seem to help any.
Thanks - Jerry

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Old 07-19-2007, 03:55 PM
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Move the throttle very slowly and check the pump shot. they should shoot the very instant you move the throttle. I used to have a holley that had a problem like this, if you moved the throttle quickly no hesitation and a good shot, if you moved it slowly a bad bog and no shot. Another engine had a bad hesitation, yet the carb and everything else was great on it, it had this annoying dead spot at always the same spot that wouldn`t go away. Come to find out the intake was warped and it had a vaccum leak, funny thing was, it never used a drop of oil. and there wouldn`t be any signs of oil in the plenum when the carb was removed. I checked the top of the intake with carb cleaner and found no leaks there either. But the signs were there, certain header tubes were white and higher than normal tempatures but it didn`t overheat. I removed the intake and took it to my machinist, he placed it on a straight sander, and found the warpage, he then milled it .010 and it didn`t clean up, he milled it another .010 to make it .020 and the warpage was still there, I threw the intake on his scrap pile and bought a new one.
I`d recommend you check it very closely for vaccum leaks.
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Old 07-20-2007, 03:48 PM
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Flat spot

Here is more info - idles at 13" vacuum - don't remember the cam specs(if I remember right it is around .501 lift on flat tappet cam) - 4 spd trans - One thing I just noticed is that if I close up the choke about 1/2 way and than give it the gas the engine revs immediately(no hesitation) does that indicate the need for more pump shot or adjustment to the rods/jets?
Thanks for your help - Jerry
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Old 07-20-2007, 04:50 PM
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Yes, you have a jetting (lean) issue......Or, the primary springs are a little weak for your combo.
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