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 Post Posted: Sat Dec 24, 2011 11:13 am 
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I have a question on the main jets role in a holley metering block.
Doesn't the main jet help the calibration for the mid range of the carburetor metering and you use the power valve restriction channels to get the full power calibration.
A few years ago was helping a guy on a alcohol engine on his dyno. He kept telling me it needed more main jet and he finally got to the point of using the largest jets he had.
He called his carb builder and he said hell just remove the main just completely and rerun the engine.
He called his carb guy back and said it was fine then.
Didn't know at the time but shouldnt he have worked with the power valve restiction channels to get the calibration right.
Thanks for the help
Randy


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 Post Posted: Sat Dec 24, 2011 12:02 pm 
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Don't think so.....Was it a 3 circuit Dominator??? I had the same issue with gas....went from a 80 jet to a 92 with no change..

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 Post Posted: Sat Dec 24, 2011 12:18 pm 
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I don't remember what carb it was but it was't a dominator.
I think the engine was a 406 small block chevy circle track engine if i remember right. It's been a few years.
Randy


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 Post Posted: Sat Dec 24, 2011 12:20 pm 
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Im' curious, what effects can it have by completly removing the main jet from the main well.
I have been told that that actually leans the calibration out.
Randy


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 Post Posted: Sat Dec 24, 2011 12:51 pm 
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If you get to the point that you can't get the jet large enough there is a restriction upstream that needs to be fixed. For a Holley style carb, the main jet MUST be the restriction in the circuit or none of it works the way it was designed. Emulsion doesn't respond as designed, main jets don't make the fuel flow changes needed. Methanol usually shows this as the volume required is roughly doubled over gas. 4150's can be made to flow enough, Dominators are a bit more troublesome. The size of the booster banjo becomes a restriction, there is not enough material to drill out to get the passage size correct. There are ways to make it work, adding an intermediate circuit with the right billet blocks will allow enough fuel with the right modifications.


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 Post Posted: Sat Dec 24, 2011 12:52 pm 
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horsepowerfreek wrote:
Im' curious, what effects can it have by completly removing the main jet from the main well.
I have been told that that actually leans the calibration out.
Randy

That can make it worse, the threads can cause turbulence and actually slow the fuel delivery.


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 Post Posted: Sat Dec 24, 2011 1:05 pm 
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I can't believe the carb builder told him to remove the jet.
With out the restriction of the jet wouldn't that effect the calibration of the main idle restriction and the effects of the emulsion well holes.
Would have resizing of the power valve restriction channels helped any.
I am wondering if the carb was even calibrated for alcohol in the first place.
After he moved away and i didn't help him anymore I had began doing a lot of research on a lot of things
and i found out there were a lot of practices that he did were not correct.
Randy


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 Post Posted: Sat Dec 24, 2011 4:03 pm 
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Randy, you have a PM!!! ;-)

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 Post Posted: Sun Dec 25, 2011 2:20 am 
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I'm not aware of anyone producing a power valve extension for the rear bowl to keep the PVCR from becoming uncovered under hard launch. ;-) [-X


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 Post Posted: Thu Dec 29, 2011 8:43 pm 
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Scott Smith wrote:
I'm not aware of anyone producing a power valve extension for the rear bowl to keep the PVCR from becoming uncovered under hard launch. ;-) [-X


I can make them if you need one. I'd prefer not to use a power valve in the rear though -- which I suppose was your point ;)


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 Post Posted: Thu Dec 29, 2011 9:43 pm 
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I run power valves square in both my gas carbs but that's a dual carb sideways mount and the reason I do that is so I can jet square. Other than that, I don't see a reason to spend money doing something that no one else does, ie, rear bowl PV extension? Having to run fuel through a greater length of fuel channel is probably going to hork up the AFRs anyway so why bother? Any time you change length or diameter of a fuel passage, you change actual flow rates. The only way to get around that is to have that channel 4x the metering orifice area so you get into a "can of worms" so to speak. Sometimes K. I. S. S. is more important, now isn't it? ;-)

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