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My mix is great until I hit 4K then it leans right out.   I changed to an f6 emulsion tube which helps a lot but still, I worry.  I have a 140 main, 125 air. 65 idle.  It is fine when it hits the second circuit.  I am running about 3.5 lbs of fuel pressure, 35mm on a plastic float.  Otherwise stock DGV,  123 with an MSD 6A.  

 

 

 

 

 

 

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You mean the primary jetting?

 

The usual fix would be to put in a smaller air corrector, but yours is already tiny.

 

By 4k, it seems like you'd have the secondary open, too....

it might be having trouble on the transition?

 

Have you tried a larger main fuel jet?

t

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Yes on the primary. If I go up to a 145 on the primary it doesn't come off of full rich (AFR 10 or less).  The problem is first gear if I pull more than 4K. 

 

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I'm gonna be that guy- "SHIFT!!!!"

 

First is too low to be much use for long, so if you shift to second at 4, you're still geared

low enough to pull hard in 2nd.  Then you can get onto the secondary, and all will be well.

 

--^^worst answer ever^^--

 

However, I'm struggling to come up with a better one.  Thinking with the keyboard,

the carb primary is going lean at part throttle, high vacuum.  That's usually calling

for a bigger jet, or smaller air corrector.  But like you, I always found the primary wanted

a pretty small main jet for low- throttle drivability and high speed cruise.  Smaller air corrector-

you're already there.  The emulsion is tied to the air corrector, and with a tiny corrector,

it's going to have a more- limited effect.

Have you checked the fit of the auxiliary venturi in the bore?  Is that even a thing for a 32?

Maybe adjust the crossover point to the secondary?  Bigger idle on the secondary?

 

Oh, wait, I've got it-

 

time for a 38/38.  You'll have so many new ratio problems, this will fade into the wallpaper!

 

Sorry, I obviously don't have anything, here.

 

t

 

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LOL. Toby I always love your answers.  I was thinking 38/38 for a second, but then I realized that I all I would likely do is change my problems.  

 

I am running on an F6 emulsion which actually helped.   If you believe the Webber handbook, either an F20, F34 or F35 will do little for the bottom end and fatten up the top end.  I will leave well enough alone for now, but  I think you are right in shifting.  I have a shift light on order.

 

Maybe when I finish the AC I will play around with this further. 

 

Regards

 

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You are trying to make power above 4000 rpm on just the primary? You do realize the primary throttle plate is not completely open at the point the secondary throat STARTS to open?  It is going lean because you have a massive intake restriction and the venturi can't supply enough fuel because the velocity at the venturi is not going up any more.   

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Oh, Byron reminded me- are you sure the secondary's closed when this happens?

 

t

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I am more concerned about burning a hole in the piston.  I am not sure why... 

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Just now, TobyB said:

Oh, Byron reminded me- are you sure the secondary's closed when this happens?

 

t

Yes, I can feel it on my foot when I touch the secondary. 

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Ah, well, that shoots theory #17-

that the secondary's a big air leak at first,

and that's what's leaning you out.

 

If it's not going lean at hard throttle, lean transients don't

do all that much damage, as long as they're not promoting

detonation.  It's when the engine is working hard under

load that lean can cause so much damage.

 

t

 

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The only car that I have owned that had detonation was my old Camaro with a 305 and a soft cam.  I am not sure that I know what to listen for.  It pulls cleanly right up to redline, no breaking up or anything. Maybe the 123 and MSD help with that. 

 

 

 

 

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I have been reading the Weber carb book.  It states that the lower the hole in the emulsion tube, the higher the revs that it will effect. More holes = leaner, less holes = richer. 

 

Soooo. I had an extra F50 emulsion tube and I filled the bottom two sets of holes with solder and it really brought the top end around to the point where it will be at about 13.5-14 at 5K on the primary only (1st gear).  Now I don't drive around like that obviously, but it is good to know that it is tuned correctly and not pegging full lean (20+).  

 

It is interesting playing with these emulsion tubes.  I am not sure that C.D Diesel's suggestion to close the secondary enrichment hole has the same effect.  I would like to know. 

 

Regards 

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Well, neato- thanks!  I haven't yet tried much with emulsions, and I think I should.

 

i can solder, and I'm a pro at putting holes in things, too!

 

t

 

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LOL.  I just used some simple electronics solder, and a soldering iron, then cleaned it up with a file. 

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