post #136 of Old 01-11-2011, 09:33 AM
mcmud
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I prefer to shop either of these two. Both will provide fast, courteous service. A phone call will be necessary since neither has the .080 listed on the site, skip the .075.
Contact Anna or Carlos @ the number listed here: http://www.carbsonly.com/frames/webermain.htm or Stephen @ http://www.piercemanifolds.com/

With the DGV having been built with either the "BIG" (74409.xxx) or the "SMALL" (74403.xxx)primary idle jet you would need to confirm which is necessary for that bore. This link will help with determining which you need.

http://www.piercemanifolds.com/category_s/191.htm

W.D.E.!

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post #137 of Old 01-15-2011, 11:56 AM
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Hello again guys. Last time I checked idle air bleeds were been drilled tapped and brass plugs threaded in with calibrated holes in them I wonder if plugging those bleeds with JB weld and instead drilling the idle jet holders would be better, like the IDAs, you could have several jet holders with different holes and changing settings should be quick and easy, small hoses could run from the heads of the holders to the air cleaner for clean air.
Jorge.
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post #138 of Old 01-15-2011, 12:02 PM
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Also, I was never able to make the F50 tube to work, I tested the F8, F80, F7, F6 and anther one I can recall right now and I was able to make the F6 work well but using small jets all around (for the primary in a 32/36) that is what I'm using now, at the end of the day the weber tuning manual recommends starting with a main that is about 4 times the size of the venturi, in my case that would be a 105 main jet (104 actually).
Jorge.
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post #139 of Old 01-15-2011, 12:11 PM
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Shouldn't that have been read as 4 X the carb bore, as a starting point.
Four times 32mm = 128mm.
Four times 36mm = 144mm
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post #140 of Old 01-15-2011, 12:30 PM
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Well... the weber tuning manual I have (the white with red lettering) says venturi, I just checked very quickly it must be obsolete then since I haven't opened in a long time, I have not looked to confirm the ratio.
Jorge.
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post #141 of Old 01-15-2011, 12:39 PM
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I wouldn't call it obsolete but I do wonder if that was written in reference to a variable choke & venturi Weber and who the author is.
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post #142 of Old 01-15-2011, 12:50 PM Thread Starter
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I have a graph that gives a starting point for main jet based on venturi size as well. Mine's geared for independent runner applications though. Maybe that's the difference.


Shawn

Live in a way that those who know you but don't know God will come to know God because they know you.
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post #143 of Old 01-15-2011, 12:55 PM
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The author is the weber factory, and I have never heard of a variable venturi weber, I'm not saying that it doesn't exist since I'm just an amateur, the only ones I have seen and worked on them are from Stromberg, keihin, SU I have two SU in our MG Midget in the garage, had 2 zenith-stromberg in our 1979 range rover way back when (and never had problems by the way), I know that Ford had one and Chrysler too but never seen them.
Jorge.
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post #144 of Old 01-15-2011, 12:57 PM
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Hi Shawn, I put the book away already but I think I saw a multiplying factor to the single cylinder graph for the multi-cylinders.
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post #145 of Old 01-15-2011, 01:00 PM
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Ohh I forgot the Amal's in the Triumph
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post #146 of Old 01-15-2011, 01:01 PM
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I see where my confusion is resulting from. It is written as 4 X venturi and then an example 4X32=128, however I always assumed it should be written as bore, since the numbers are in line with what Redline has jetted both the fixed venturi 32/36DGV and 38DGS.

And then I used the term "variable" for the choke and venturi type Webers which you may select and set their sizes.
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post #147 of Old 01-15-2011, 01:08 PM
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Yes it is confusing since the way we usually refer to these carbs are with the bores, but the graphs are general graphs to fit all webers and it it just our series that doesn't have interchangeable venturis, it is very common to find a 40DCOE with 32mm venturi and another with 36mm both needing different jets (well... maybe or maybe not).
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post #148 of Old 01-15-2011, 02:34 PM
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Lets look at an example using both formulas with the 32/36DGV as well as the 38DGS and then comparing those results with what Redline recommends to be used in our typical 4.2 applications.

DGV 26mm X 4 = 104 and then 27mm X 4 = 108
Since they are staggered, I might assume that we could average the two so that being 26+27=53 time 4 equals 212 / 2 = 105. Redline suggest that we begin at 145.

While considering the bores. 32 X 4 = 128 and 36 X 4 = 144 then if we average those two it equals 136.

While we see that either of these examples fall short of the sizes that are considered the basis with our applications we must remember that the DGV is actually designed for a smaller engine than the 4.2 inline six, however you will see that with the bore being the factor it is much nearer the typical standard.

Looking to the 38DGS, 27 X 4 = 108. Redline suggest 140-150's. When we consider the bores being 38mm X 4 = 152

Then taking those sums a bit farther in the trial to begin fitting the idle jets in a DGV.

While using 105 X .42 we see that the idle jets should be in the range of .044. While using the bore we see that 136 time .42 equals a range of .057 Redline recommends a 075 primary and a 060 secondary.

And with the DGS at the venturi, 27 X 4 = 108 * .42 = .045
Using the bore rather than the venturi, 38 X 4 = 152 X .42 = .063. Redline recommends 055-060
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post #149 of Old 01-17-2011, 03:14 PM
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Quote:
Originally Posted by mcmud View Post
Lets look at an example using both formulas with the 32/36DGV as well as the 38DGS and then comparing those results with what Redline recommends to be used in our typical 4.2 applications.

DGV 26mm X 4 = 104 and then 27mm X 4 = 108
Since they are staggered, I might assume that we could average the two so that being 26+27=53 time 4 equals 212 / 2 = 105. Redline suggest that we begin at 145.

While considering the bores. 32 X 4 = 128 and 36 X 4 = 144 then if we average those two it equals 136.

While we see that either of these examples fall short of the sizes that are considered the basis with our applications we must remember that the DGV is actually designed for a smaller engine than the 4.2 inline six, however you will see that with the bore being the factor it is much nearer the typical standard.

Looking to the 38DGS, 27 X 4 = 108. Redline suggest 140-150's. When we consider the bores being 38mm X 4 = 152

Then taking those sums a bit farther in the trial to begin fitting the idle jets in a DGV.

While using 105 X .42 we see that the idle jets should be in the range of .044. While using the bore we see that 136 time .42 equals a range of .057 Redline recommends a 075 primary and a 060 secondary.

And with the DGS at the venturi, 27 X 4 = 108 * .42 = .045
Using the bore rather than the venturi, 38 X 4 = 152 X .42 = .063. Redline recommends 055-060
This is very good information and a great place to start "jetting". The carburetors come from Spain with larger jets than this. I believe it has to do with the pump gas we can expect to run and the sizes of the engines have increased in the US. Good stuff here....
I wanted to comment on the size of the Venturi, as the size increases the depression or the vacuum pulling the fuel decreases, therefore needing a larger jet and conversley when the Venturi size decreases the signal increases needing a smaller jet. Then there is... What does the engine like? Once we start we can go leaner until the engine won't run, or, richer until we are blowin black smoke out the exhaust. Somewhere in the middle of all of this is a cruise Lambda reading and a power reading. This is where we need to tune to our specific needs from our equipment.
This is a great conversation.
Uptillnow
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post #150 of Old 01-17-2011, 03:27 PM
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P.S.
I know the signal does not pull. The atmospheric pressure push the fuel to fill the void created by the Vena contracta on the venturi. (Bernouli's Principle) Also the air speed (or RPM) has to be considered. This is why I like to respond to the needs of the engine.
tillnow
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