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 Post Posted: Thu Feb 26, 2009 12:16 pm 
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Gas contaminated oil won't help for sure....I don't think plugs will do much for you as it didn't do anything for me...

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 Post Posted: Thu Feb 26, 2009 2:12 pm 
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Blackened plugs will dissipate heat faster than a clean plug and not burn fuel as well, it will act like a significantly colder plug. Change them if they are black.


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 Post Posted: Thu Feb 26, 2009 2:18 pm 
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Beretta wrote:
Gas contaminated oil won't help for sure....I don't think plugs will do much for you as it didn't do anything for me...


Yeah, I was thinking that myself. My thought was that it will probably clean the ends off pretty good now that it's leaned down at idle and part throttle. As long as the electrode isn't rounded off I think I'd run'em until you go to the track to test and even then I probably wouldn't use but a couple to see where you were with the fuel ring.

Iff'in that's a BBC with a single carb single plane intake I'll bet that the corners will be leaner than the center cylinders. Donee has that problem with his and so do I with my SBC. Your mileage may vary though.

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 Post Posted: Mon Jun 04, 2012 11:04 am 
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Ron Gusack found this post in another thread here back 2008 and though it might be relevant to this section. So I'm going to post it here as an "add on" for those dealing with T slot and idle stuff.

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When you look through the closed throttles at a light is the light leakage evenly distributed around the periphery of the throttles? You might gain some closing if you loosen the screws just a bit and shuffle the blades around for a better fit. Scott’s carb is like yours and it seems to work OK.

Except in a true 1-to-1 carburetor, it isn’t necessary that the T-slot is exposed on the secondary like it should be on the primary. The random location of T-slots in 4500’s makes them a crap shoot so consequently what’s desirable may not always be possible and as a result any effort must suit the situation of the individual carb. There can be several conflicting requirements of the particular carb and engine marriage, vertical location of the slots vs. airflow necessary for idle speed desired, etc.

For a staged throttle, I think it’s better if the slot is blanked off by the secondary blade so it’s not involved in the fueling when the secondary isn’t actually in use. Unfortunately, like in Scott’s case where the slots are low in the bore, you have to take what you get and deal with it. You can lengthen and so lower the bottom of a slot that’s too high in the bore but it’s hard to make them shorter.

The reasoning for closing the secondary T-slot is because the exposed fuel feed area at the curb idle is subject to the increase of manifold vacuum that occurs at higher engine speeds with closed or small throttle openings like decelerating or in steady state cruising on the street or return road, etc. When more T-slot area is exposed because the secondary is set to show some slot, the result is more fuel flow from the secondary idle system even though the secondary butterfly is on the idle stop, just because there is more vacuum. This is one of the reasons some carbs get so rich in a steady-state cruise.

The fuel coming through the idle mixture adjustment screw is subject to one more throttling (by the screw point) than the T-slot. When the t-slot is cut off it assumes its role as a larger idle system air bleed and more air is being throttled by the mixture screw for the same amount of fuel (the amount required for curb idle). Just like a larger IAB up top, this makes the discharge less sensitive to manifold vacuum fluctuations.

Often, the throttle positions immediately off-idle, the smallest throttle openings, are troublesome to get absolutely smooth. That part of tuning a carb on a radical engine can consume more time than the rest of it. This is especially so with street-driven cars where the majority of time is spent in a steady-state low speed cruise and that throttle position comes under a lot of scrutiny. Changing the secondary idle position, more closed or further open, requires a corresponding change on the primary to maintain the desired idle speed and re-adjustment of the mixture screws. This is about the easiest change you can make that affects the nearly closed throttle position and many times can be the cure for a glitch in that spot.

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